Emerging Trends in The Social and Behavioral Sciences

Disorders of Consciousness

Item

Title

Disorders of Consciousness

Author

Monti, Martin M.

Research Area

Psychopathology

Topic

Mental Disorder Varieties

Abstract

Disorders of consciousness are a spectrum of neurological disorders, encompassing coma, the vegetative state, and the minimally conscious state, in which patients acquire or develop an impairment of the two cardinal elements of consciousness–wakefulness and awareness. One of the main sources of complexity in this context is how to recognize and tell apart patients who retain some level of awareness from patients who do not. Indeed, in the absence of any direct means of assessing one's level of awareness, we are forced to indirectly infer a patient's state on the basis of their ability to perform behaviors that, appearing clearly voluntary, imply the presence of consciousness. In this contribution, we explore recent evidence showing how brain imaging can be harnessed to address the problem of consciousness in patients surviving severe brain injury. First, we focus on recent experiments demonstrating how neuroimaging can be used to detect the presence of voluntary “brain behavior” in otherwise non responsive patients, and to allow a rudimentary form of non muscle‐dependent communication strategy based solely on voluntary brain activity. Second, we discuss recent findings concerning network activity at different levels of awareness, and the relationship between thalamo cortical circuits and consciousness.

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Identifier

etrds0077

extracted text

Disorders of Consciousness
MARTIN M. MONTI

Abstract
Disorders of consciousness are a spectrum of neurological disorders, encompassing coma, the vegetative state, and the minimally conscious state, in which
patients acquire or develop an impairment of the two cardinal elements of
consciousness–wakefulness and awareness. One of the main sources of complexity
in this context is how to recognize and tell apart patients who retain some level of
awareness from patients who do not. Indeed, in the absence of any direct means
of assessing one’s level of awareness, we are forced to indirectly infer a patient’s
state on the basis of their ability to perform behaviors that, appearing clearly
voluntary, imply the presence of consciousness. In this contribution, we explore
recent evidence showing how brain imaging can be harnessed to address the
problem of consciousness in patients surviving severe brain injury. First, we focus
on recent experiments demonstrating how neuroimaging can be used to detect the
presence of voluntary “brain behavior” in otherwise non responsive patients, and to
allow a rudimentary form of non muscle-dependent communication strategy based
solely on voluntary brain activity. Second, we discuss recent findings concerning
network activity at different levels of awareness, and the relationship between
thalamo cortical circuits and consciousness.

INTRODUCTION
Disorders of consciousness (DOC) are a spectrum of disorders, typically
acquired or developed following severe brain injury, in which an individual’s consciousness is altered in a transient or permanent manner owing
to severe brain injury (Monti, 2012). In this context, consciousness is (simplistically) conceived as encompassing two cardinal elements (Laureys,
2005): wakefulness and awareness. Wakefulness refers to the level of one’s
consciousness and includes states such as deep sleep, drowsiness, and full
(normal) wake. Awareness refers to the content of consciousness, a more
elusive concept relating to the degree to which an individual possesses
subjective experience (of him/herself or the surrounding environment). In
daily life, most people experience the two elements of consciousness as being
intimately tied to each other. When asleep, for example, wakefulness and
awareness are both very low and jointly return as we progress through light
Emerging Trends in the Social and Behavioral Sciences. Edited by Robert Scott and Stephen Kosslyn.
© 2015 John Wiley & Sons, Inc. ISBN 978-1-118-90077-2.

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

sleep and drowsiness toward awakening. In some circumstances, however,
these two elements dissociate from each other. During dream sleep, for
example, we commonly experience the presence of some level of (self)
awareness despite the absence of wakefulness. In DOC, we are typically
confronted with the reverse dissociation: wakefulness in the absence of (self)
awareness.
FOUNDATIONAL RESEARCH
DEFINITIONS
Coma. Coma is a state in which patients appear to lack both elements of
consciousness–they do not open their eyes even when intensely stimulated
(i.e., they have low level of consciousness) and they do not show any evidence
of awareness of themselves or of their surroundings [i.e., they have low, or
no, content of consciousness; (Monti, Laureys, & Owen, 2010)]. This state can
last from 2 to 4 weeks, with chronic coma being a rare long-term outcome.
Vegetative State (VS). While many coma patients recover within a few weeks,
a subset go on to regain some level of consciousness (i.e., “awaken” from
coma) but without regaining any content of consciousness (Monti, Laureys,
et al., 2010). This condition of “wakefulness in the absence of awareness”
defines the vegetative state (VS) (The Multi-Society Task Force on PVS,
1994). VS patients appear to periodically awaken and fall asleep, as indexed
by alternating periods of sustained eye-opening and eye-closing, but never
show any sign of purposeful behavior or (self) awareness. When this
condition lasts longer than 3 weeks, it is referred to as a persistent VS, after
which the chances of recovery decrease with time. If this condition lasts for
longer than 3 months1 (for patients who suffered from a nontraumatic brain
injury; e.g., anoxia) or 1 year (for patients who suffered from a traumatic
brain injury), a prognosis of permanent VS is made, after which chances of
recovery are typically considered to be minimal.
Until recently, the VS was believed to be a condition in which basic
vegetative nervous functions (including thermoregulation, respiration, and
sleep-wake cycles) are preserved, but in the complete absence of sensation or
thought–a view that is well captured by the term apallic syndrome (from the
Latin word a-pallium, “without a cortex”), sometimes used to describe these
patients. However, taking stock of about 15 years of neuroimaging research
in this cohort, employing tools such as positron emission tomography (PET),
functional magnetic resonance imaging (fMRI), and electroencephalography
1. In the United Kingdom, the threshold for a VS to be considered permanent after nontraumatic insult
is set at 6 months.

Disorders of Consciousness

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(EEG), it has become increasingly clear that several aspects of cortical
function, including somatosensory (Boly et al., 2008), nociceptive (Laureys
et al., 2002), auditory (Kotchoubey et al., 2005), and semantic (Schnakers
et al., 2008) processing, among others, can remain even in the absence of
consciousness [see Monti (2012) for a recent comprehensive review].
Minimally Conscious State (MCS). Some patients remain in VS indefinitely.
Other patients, however, go on to regain some degree of awareness, thereby
progressing to a minimally conscious state (MCS) (Giacino et al., 2002). MCS
patients are defined as being awake and able to show, if intermittently, reproducible signs of (self) awareness in the form of purposeful (i.e., non reflexive)
behavior. An MCS patient, for example, might be able to demonstrate pursuit eye-movements toward salient stimuli in the environment, reaching for
objects, or even the production of (appropriate) vocalizations or gestures in
response to questions and commands. Minimally conscious patients might
remain in this condition indefinitely, or might further recover, emerging from
MCS, as they regain the ability to functionally/appropriately use objects or
accurately communicate (verbally or gesturally).
THE CONUNDRUM OF (FINDING) CONSCIOUSNESS
The definitions above, by which we differentially diagnose patients suffering
from DOCs, highlight one of the most crucial (and fascinating) questions in
this field: how can we tell if an individual, other than ourselves, is conscious?
Indeed, in the absence of a means to directly measure one’s consciousness,
the distinction between what most people would regard as “conscious” and
what most people would regard as “unconscious” relies on the pragmatic
principle by which the presence of voluntary (i.e., non reflexive) behavior
is taken to imply the presence of consciousness (Monti, Coleman, & Owen,
2009b). This principle of revealed consciousness is the bedrock upon which
current clinical assessments rely. If a patient can demonstrate any kind of
purposeful or voluntary behavior in response to stimulation (e.g., responding to a command such as “move your foot”), an MCS diagnosis is made.
Conversely, if a patient fails to demonstrate any sign of purposeful behavior,
a VS diagnosis is made. This reasoning, however, is logically flawed in that
it takes the absence of evidence of consciousness (e.g., absence of purposeful behavior) to be evidence of absence of consciousness (Monti et al., 2009b).
What if a patient were conscious but unable to perform any recognizably voluntary behavior due to motor impairment? What if a patient were conscious
but aphasic, and thus unable to make sense of a clinician’s request to perform
a certain behavior? What if a patient was conscious but did not possess sufficient residual cognitive functions to successfully comply with a clinician’s

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

instruction? In all these cases, a patient would be diagnosed as being in VS,
despite retaining some level of (self) awareness. Confirming this view, several
studies, including retrospective audits (Andrews, Murphy, Munday, & Littlewood, 1996; Childs, Mercer, & Childs, 1993) and comparisons of diagnostic
methodologies (Schnakers et al., 2006, 2009), have reported a consistent 40%
misdiagnosis rate by which (minimally) conscious patients are incorrectly
considered to be unconscious (i.e., vegetative). While a number of different
causes might underlie the totality of these cases (e.g., lack of skill or training in specific clinical assessments, limited knowledge of this relatively rare
condition, and confusion in terminology), the presence of sensory and motor
impairment are well known to potentially mask the presence of consciousness by virtue of rendering the patient unable to either understand or comply
with a clinician’s attempt to elicit purposeful behavior (Monti, Laureys, et al.,
2010). In what follows, I will briefly cover the two main approaches that,
today, are being developed in order to overcome this “conundrum” of consciousness (Owen & Coleman, 2008).
CUTTING-EDGE RESEARCH
COGITO ERGO SUM BY NEUROIMAGING2
In 2006, a radical idea was introduced in the field as a potential solution to the
conundrum of consciousness (Owen et al., 2006). If some patients are (at least
minimally) conscious, but unable to produce overt behavior because of motor
impairments, maybe they might be able to engage in some form of recognizably voluntary “mental behavior” detectable through modern neuroimaging
techniques, thereby revealing a state of consciousness (Monti & Owen, 2010).
Consistent with this intuition, a number of patients who appeared behaviorally unresponsive in standard (behavior-based) clinical assessments were
shown to be able to willfully engage in a motor and a spatial mental imagery
task (i.e., imagining playing tennis and imagining walking in a familiar environment), eliciting the same neural substrate that is typically seen in healthy
individuals engaging in the same task, and thereby signaling a state of consciousness (Monti, Vanhaudenhuyse, et al., 2010; Owen, et al., 2006).
If a patient can engage at will in (at least) two mental tasks that can be distinguished from each other on the basis of neural activity, this ability can be
harnessed into a basic non motor-dependent communication strategy: a “language” made of any two possible alternatives (e.g., “yes/no” and “on/off”).
In agreement with this intuition, a patient who was initially believed to be in
a permanent VS was recently shown to be able to respond to autobiographical questions by engaging in one kind of imagery (e.g., playing tennis) to
2. Ropper (2010).

Disorders of Consciousness

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convey an affirmative answer and in a different kind of imagery (e.g., walking around his home) to convey a negative answer (Monti, Vanhaudenhuyse,
et al., 2010). This finding was recently confirmed when a VS and an MCS
patients were shown to be able to use selective attention (i.e., the process
of focusing on a relevant stimulus while attempting to filter out irrelevant
ones) to respond to binary questions (Naci & Owen, 2013). This new procedure takes the approach presented in Monti, Vanhaudenhuyse, et al. (2010)
one step further by granting patients the ability to choose from a number of
potential answers rather than constraining them to two alternatives only. In
this novel procedure, patients are not asked to elicit different mental states
to give a positive or negative answer, but rather are presented aurally with
a number of possible answers (e.g., “yes, no, one, two, three, … ”) and then
asked to covertly count the number of times the answer they want to convey
is repeated. The timing of the observed brain activations can then be used to
infer which word (i.e., answer) a patient was focusing on.
Amidst these groundbreaking results, however, it is important to consider
that the dissociation between motor and brain responsiveness can go both
ways. As discussed above, some patients who appear unresponsive in
clinical (motor-based) assessments can appear responsive in neuroimaging
(brain-based) assessments. Conversely, some patients who appear responsive in clinical assessments can appear unresponsive in neuroimaging
tests–despite being able to verbally report that they were engaging in the
mental activity as instructed (Bardin et al., 2011), highlighting the complexities of interpreting negative findings in neuroimaging, and the need to
integrate standard and neuroimaging assessments (Monti, 2013).
TOWARD A NEUROPHYSIOLOGY OF DOC
Despite the flourishing of research in this field, we still have a very limited understanding of the physiological mechanisms underlying the loss and
(sometimes) recovery of consciousness after severe brain injury. In particular,
it is unclear why patients in a VS can retain several degrees of cortical activity
while failing to experience the feeling of (self) awareness.
Until recently, a prominent view held that VS patients only maintained
residual information processing in primary sensory cortices (Boly et al., 2004;
Laureys et al., 2002) without it propagating to higher-level and polimodal
integration areas that are considered necessary for conscious experience
(Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006). The evidence
available to date, however, does not seem to support this idea. Indeed,
neuroimaging studies have now amply shown that VS patients can exhibit
information processing outside primary cortices. A recent set of studies,
however, might suggest a different hypothesis accounting for the presence

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

of extensive cortical processing in the absence of consciousness. Under this
view, the VS might best be characterized as a “disconnection syndrome”
(Laureys, 2005; Schiff, 2010) whereby residual brain processing in VS
patients might reflect isolated cognitive modules that, in the absence of
global integration, do not generate conscious experience (Monti, 2012).
Loss of Connectivity in DOC. Taking advantage of non invasive neuroimaging (and particularly task-free, or “rest,” approaches) a growing amount of
evidence suggests that DOC are characterized by a decrease in connectivity across frontal, parietal and temporo parietal regions. Specifically, a set of
regions often referred to as the default mode network, show decreased connectivity in proportion to the severity of the impairment of consciousness (Vanhaudenhuyse et al., 2010). Similarly, it has also been shown that minimally
conscious and VS patients differ significantly in the extent of “top-down”
connectivity extending from prefrontal cortex to superior temporal regions
(Boly et al., 2011), with the latter group of patients exhibiting a marked reduction. Assessing cortico cortical correlations and directional connectivity, however, does not bear much explanatory power vis-à-vis the question of why
they are so important for the maintenance (or generation) of consciousness.
To start addressing this question, and converge toward a more mechanistic understanding of the relationship between brain function and consciousness, a recent study investigated the effect of anesthetic agents on the network properties of the brain (Monti, Lutkenhoff, et al., 2013). Specifically, a
set of healthy volunteers underwent a resting state fMRI recording at different levels of consciousness: awake, sedated, unconscious, and recovery
(i.e., after having regained consciousness). Unlike the previous connectivity
studies, however, brain function was not assessed on the basis of the intensity of point-to-point correlations, but rather using tools derived from a relatively recent branch of mathematics—graph theory—which allows assessing
the brain as a network of nodes exchanging information (within the boundaries of the resolution offered by fMRI). In this study, the only unambiguous
signature of a state of unconsciousness, with respect to how information is
exchanged in brain networks, was a marked decrease in global efficiency. In
other words, the unconscious (healthy) brain suffers from a global decrease
in the efficiency with which information from distant parts of the brain can
be integrated. One intriguing aspect of this finding, which is awaiting replication in patients, is that consciousness might best be thought of as a how
(i.e., a mode of brain functioning) rather than a where–an idea that matches
the view proposed by a prominent theory of consciousness [i.e., Integrated
Information Theory of Consciousness; (Tononi, 2008)].

Disorders of Consciousness

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Thalamo-cortical Circuits in DOC. If indeed the loss of consciousness is related
to a loss of global information integration across distant regions of cortex,
the next step requires understanding the causes leading to these changes in
brain function. In general, thalamus has always been considered important
for the maintenance of consciousness. Indeed, post-mortem and neuroimaging examinations have revealed severe tissue death in thalamus (and hippocampus; (Adams, Graham, & Jennett, 2000)), as well as structural damage
in sub cortical white matter (Fernandez-Espejo et al., 2011), in this cohort of
patients. Today, a number of experiments seem to indicate that specific cortico subcortical circuits—uniting, among other regions, frontal and parietal
cortices, and medio dorsal thalamus–might be crucial to the integration of
information across distant loci of cortex (Schiff, 2010). Indeed, a recent study
has shown that, in acute severely injured patients, the degree of secondary,
non mechanical, damage to thalamus, and consequential atrophy in the anterior and dorso-medial areas occurring over the first 6 months post injury, is
predictive of chronic outcome (Lutkenhoff et al., 2013). Consistent with this
finding, chronic DOC patients have been shown to have, as a group, atrophy
along the medio dorsal axis of thalamus, when compared to healthy volunteers (Fernández-Espejo et al., 2010). Although this latter study reported no
differences between conscious (i.e., MCS) and unconscious (i.e., VS) patients,
the findings are consistent with the data observed in the acute setting. Finally,
the view that thalamo cortical circuits play a key role in DOCs is also consistent with a number of case studies. First, a patient was shown to specifically
recover thalamo frontal connectivity in concurrence with the reemergence
of consciousness (Laureys et al., 2000). Second, deep brain stimulation to the
antero medial regions of thalamus have been shown to have beneficial effects
in terms of improved responsiveness in DOC patients (Schiff et al., 2007).
Finally, it was recently shown that a patient with disrupted thalamo cortical connection was in a state of un consciousness despite the preservation of
cortico cortical (i.e., “default mode network”) connectivity (Boly et al., 2009),
thus potentially carving out very different roles, in the generation of consciousness, for thalamo cortical versus cortico cortical circuits.
KEY ISSUES FOR FUTURE RESEARCH
WHAT IS IT LIKE TO BE IN A VEGETATIVE STATE?
One issue that is still to be clarified is “what is it like” to be at the lower
boundaries of consciousness. More specifically, despite the flurry of recent
studies demonstrating the preservation of visual processing (Monti, Pickard,
& Owen, 2013), auditory and linguistic processing (Kotchoubey, et al., 2005),
attention (Monti, Coleman, & Owen, 2009a, Monti et al., in press), and even

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learning (Bekinschtein et al., 2009), it is unclear the degree to which mental life
can remain in DOC patients (Ropper, 2010), whether they can feel any pain
(Schnakers, Chatelle, Demertzi, Majerus, & Laureys, 2012; Schnakers et al.,
2010), or form lasting memories.
HARNESSING BCI FOR COMMUNICATION IN NON RESPONSIVE PATIENTS
A significant portion of the research described above shows that some
DOC patients can retain (a varying level of) (self) awareness even if behaviorally unresponsive. It is therefore important, for these cases, to develop
methods that might, through training algorithms, harness computers as
“brain-computer-interfaces” (BCI) that can be used for nonbehavioral
patients to interact with their environment (Naci et al., 2012).
THE TREATMENT GAP
One notable issue, in the context of DOCs, is that despite our increasing
sophistication in estimating the level of residual cognition and awareness
that might be retained after severe brain injury, there is today no standard
treatment available for these patients [there is, however, very exciting evidence that administration of amantadine accelerates the pace of functional
recovery in some post-traumatic DOC patients (Giacino et al., 2012)].
FROM NEUROSCIENCE TO CLINICAL PRACTICE, LAW, AND ETHICS
Finally, it is worth considering that our theoretical and practical advances
in this field bear repercussions outside the domain of science (Monti, 2013).
First, what is now considered science is still in search of a practical role in
medical care–a transformation that will require studies with much larger
samples than those typically carried out today. Second, an increased effort
in understanding the degree of mental life and cognitive processing possible
in minimally responsive individuals is necessary to allow a substantial discussion concerning which rights–if any, should be recognized to the patients
with respect to their participation in the medical decision making process
and, ultimately, self-determination (Peterson et al., 2013).
REFERENCES
Adams, J. H., Graham, D. I., & Jennett, B. (2000). The neuropathology of the vegetative state after an acute brain insult. Brain, 123(Pt 7), 1327–1338.
Andrews, K., Murphy, L., Munday, R., & Littlewood, C. (1996). Misdiagnosis of
the vegetative state: Retrospective study in a rehabilitation unit. BMJ, 313(7048),
13–16.

Disorders of Consciousness

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Bardin, J. C., Fins, J. J., Katz, D. I., Hersh, J., Heier, L. A., Tabelow, K., … Voss,
H. U. (2011). Dissociations between behavioural and functional magnetic resonance imaging-based evaluations of cognitive function after brain injury. Brain,
134(Pt 3), 769–782. doi:10.1093/brain/awr005
Bekinschtein, T. A., Shalom, D. E., Forcato, C., Herrera, M., Coleman, M. R., Manes,
F. F., & Sigman, M. (2009). Classical conditioning in the vegetative and minimally
conscious state. Nature Neuroscience, 12(10), 1343–1349. doi:10.1038/nn.2391
Boly, M., Faymonville, M. E., Peigneux, P., Lambermont, B., Damas, P., Del Fiore,
G., … Laureys, S. (2004). Auditory processing in severely brain injured patients:
Differences between the minimally conscious state and the persistent vegetative
state. Archives of Neurology, 61(2), 233–238. doi:10.1001/archneur.61.2.233
Boly, M., Faymonville, M. E., Schnakers, C., Peigneux, P., Lambermont, B., Phillips,
C., … Laureys, S. (2008). Perception of pain in the minimally conscious state
with PET activation: An observational study. Lancet Neurology, 7(11), 1013–1020.
doi:10.1016/S1474-4422(08)70219-9
Boly, M., Garrido, M. I., Gosseries, O., Bruno, M. A., Boveroux, P., Schnakers, C., …
Friston, K. (2011). Preserved feedforward but impaired top-down processes in the
vegetative state. Science, 332(6031), 858–862. doi:10.1126/science.1202043
Boly, M., Tshibanda, L., Vanhaudenhuyse, A., Noirhomme, Q., Schnakers, C.,
Ledoux, D., … Laureys, S. (2009). Functional connectivity in the default network
during resting state is preserved in a vegetative but not in a brain dead patient.
Human Brain Mapping, 30(8), 2393–2400. doi:10.1002/hbm.20672
Childs, N. L., Mercer, W. N., & Childs, H. W. (1993). Accuracy of diagnosis of persistent vegetative state. Neurology, 43(8), 1465–1467.
Dehaene, S., Changeux, J. P., Naccache, L., Sackur, J., & Sergent, C. (2006). Conscious,
preconscious, and subliminal processing: A testable taxonomy. Trends in Cognitive
Sciences, 10(5), 204–211.
Fernandez-Espejo, D., Bekinschtein, T., Monti, M. M., Pickard, J. D., Junque, C., Coleman, M. R., & Owen, A. M. (2011). Diffusion weighted imaging distinguishes the
vegetative state from the minimally conscious state. NeuroImage, 54(1), 103–112.
doi:10.1016/j.neuroimage.2010.08.035
Fernández-Espejo, D., Junque, C., Bernabeu, M., Roig-Rovira, T., Vendrell, P., & Mercader, J. M. (2010). Reductions of thalamic volume and regional shape changes in
the vegetative and the minimally conscious states. Journal of Neurotrauma, 27(7),
1187–1193.
Giacino, J. T., Ashwal, S., Childs, N., Cranford, R., Jennett, B., Katz, D. I., … Zasler,
N. D. (2002). The minimally conscious state: Definition and diagnostic criteria.
Neurology, 58(3), 349–353.
Giacino, J. T., Whyte, J., Bagiella, E., Kalmar, K., Childs, N., Khademi, A., … Sherer,
M. (2012). Placebo-controlled trial of amantadine for severe traumatic brain injury.
The New England Journal of Medicine, 366(9), 819–826. doi:10.1056/NEJMoa1102609
Kotchoubey, B., Lang, S., Mezger, G., Schmalohr, D., Schneck, M., Semmler, A., …
Birbaumer, N. (2005). Information processing in severe disorders of consciousness:
Vegetative state and minimally conscious state. Clinical Neurophysiology: Official

10

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

Journal of the International Federation of Clinical Neurophysiology, 116(10), 2441–2453.
doi:10.1016/j.clinph.2005.03.028
Laureys, S. (2005). The neural correlate of (un)awareness: Lessons from the vegetative state. Trends in Cognitive Sciences, 9(12), 556–559. doi:10.1016/j.tics.2005.10.010
Laureys, S., Faymonville, M. E., Luxen, A., Lamy, M., Franck, G., & Maquet, P. (2000).
Restoration of thalamocortical connectivity after recovery from persistent vegetative state [Letter]. Lancet, 355(9217), 1790–1791.
Laureys, S., Faymonville, M. E., Peigneux, P., Damas, P., Lambermont, B., Del Fiore,
G., … Maquet, P. (2002). Cortical processing of noxious somatosensory stimuli in
the persistent vegetative state. NeuroImage, 17(2), 732–741.
Lutkenhoff, E. S., McArthur, D. L., Hua, X., Thompson, P. M., Vespa, P. M., & Monti,
M. M. (2013). Thalamic atrophy in antero-medial and dorsal nuclei correlates
with six-month outcome after severe brain injury. NeuroImage. Clinical, 3, 396–404.
doi:10.1016/j.nicl.2013.09.010
Monti, M. M. (2012). Cognition in the vegetative state. Annual Review of Clinical Psychology, 8, 431–454. doi:10.1146/annurev-clinpsy-032511-143050
Monti, M. M. (2013). Ethics, Neuroimaging and disorders of consciousness: What is
the question? AJOB Neuroscience, 4(4), 1–2.
Monti, M. M., Coleman, M. R., & Owen, A. M. (2009a). Executive functions in the
absence of behavior: Functional imaging of the minimally conscious state. Progress
in Brain Research, 177, 249–260. doi:10.1016/S0079-6123(09)17717-8
Monti, M. M., Coleman, M. R., & Owen, A. M. (2009b). Neuroimaging and the vegetative state: Resolving the behavioral assessment dilemma? Annals of the New York
Academy of Sciences, 1157, 81–89. doi:10.1111/j.1749-6632.2008.04121.x
Monti, M. M., Laureys, S., & Owen, A. M. (2010). The vegetative state. BMJ, 341,
c3765. doi:10.1136/bmj.c3765
Monti, M. M., Lutkenhoff, E. S., Rubinov, M., Boveroux, P., Vanhaudenhuyse, A.,
Gosseries, O., … Laureys, S. (2013). Dynamic change of global and local information processing in propofol-induced loss and recovery of consciousness. PLoS
Computational Biology, 9(10), e1003271. doi:10.1371/journal.pcbi.1003271
Monti, M. M., & Owen, A. M. (2010). Behavior in the brain using functional neuroimaging to assess residual cognition and awareness after severe brain injury.
Journal of Psychophysiology, 24(2), 76–82. doi:10.1027/0269-8803/A000016
Monti, M. M., Pickard, J. D., & Owen, A. M. (2013). Visual cognition in disorders
of consciousness: From V1 to top-down attention. Human Brain Mapping, 34(6),
1245–1253. doi:10.1002/hbm.21507
Monti, M. M., Rosenberg, M., Finoia, P., Kamau, E., Pickard, J. D., & Owen, A. M.
(in press). Thalamo-frontal connectivity mediates top-down cognitive functions
in disorders of consciousness. Neurology.
Monti, M. M., Vanhaudenhuyse, A., Coleman, M. R., Boly, M., Pickard, J. D.,
Tshibanda, L., … Laureys, S. (2010). Willful modulation of brain activity in
disorders of consciousness. The New England Journal of Medicine, 362(7), 579–589.
doi:10.1056/NEJMoa0905370
Naci, L., Monti, M. M., Cruse, D., Kubler, A., Sorger, B., Goebel, R., … Owen,
A. M. (2012). Brain-computer interfaces for communication with nonresponsive
patients. Annals of Neurology, 72(3), 312–323. doi:10.1002/ana.23656

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Naci, L., & Owen, A. M. (2013). Making every word count for nonresponsive patients.
JAMA Neurology, 70(10), 1235–1241. doi:10.1001/jamaneurol.2013.3686
Owen, A. M., & Coleman, M. R. (2008). Functional neuroimaging of the vegetative
state. Nature Reviews Neuroscience, 9(3), 235–243. doi:10.1038/nrn2330
Owen, A. M., Coleman, M. R., Boly, M., Davis, M. H., Laureys, S., & Pickard, J. D.
(2006). Detecting awareness in the vegetative state. Science, 313(5792), 1402.
Peterson, A., Naci, L., Weijer, C., Cruse, D., Fernández-Espejo, D., Graham, M., &
Owen, A. M. (2013). Assessing decision-making capacity in the behaviorally nonresponsive patient with residual covert awareness. AJOB Neuroscience, 4(4), 3–14.
Ropper, A. H. (2010). Cogito ergo sum by MRI. The New England Journal of Medicine,
362(7), 648–649. doi:10.1056/NEJMe0909667
Schiff, N. D. (2010). Recovery of consciousness after brain injury: A mesocircuit
hypothesis. Trends in Neurosciences, 33(1), 1–9. doi:10.1016/j.tins.2009.11.002
Schiff, N. D., Giacino, J. T., Kalmar, K., Victor, J. D., Baker, K., Gerber, M., … Rezai,
A. R. (2007). Behavioural improvements with thalamic stimulation after severe
traumatic brain injury. Nature, 448(7153), 600–603. doi:10.1038/nature06041
Schnakers, C., Chatelle, C., Demertzi, A., Majerus, S., & Laureys, S. (2012). What
about pain in disorders of consciousness? The AAPS Journal, 14(3), 437–444.
doi:10.1208/s12248-012-9346-5
Schnakers, C., Chatelle, C., Vanhaudenhuyse, A., Majerus, S., Ledoux, D., Boly, M.,
… Laureys, S. (2010). The nociception coma scale: A new tool to assess nociception
in disorders of consciousness. Pain, 148(2), 215–219. doi:10.1016/j.pain.2009.09.028
Schnakers, C., Giacino, J., Kalmar, K., Piret, S., Lopez, E., Boly, M., … Laureys, S.
(2006). Does the FOUR score correctly diagnose the vegetative and minimally conscious states? Annals of Neurology, 60(6), 744–745; author reply 745.
Schnakers, C., Perrin, F., Schabus, M., Majerus, S., Ledoux, D., Damas, P., … Laureys,
S. (2008). Voluntary brain processing in disorders of consciousness. Neurology,
71(20), 1614–1620. doi:10.1212/01.wnl.0000334754.15330.69
Schnakers, C., Vanhaudenhuyse, A., Giacino, J., Ventura, M., Boly, M., Majerus, S., …
Laureys, S. (2009). Diagnostic accuracy of the vegetative and minimally conscious
state: Clinical consensus versus standardized neurobehavioral assessment. BMC
Neurology, 9, 35. doi:10.1186/1471-2377-9-35
The Multi-Society Task Force on PVS (1994). Medical aspects of the persistent
vegetative state (1). The New England Journal of Medicine, 330(21), 1499–1508.
doi:10.1056/NEJM199405263302107
Tononi, G. (2008). Consciousness as integrated information: A provisional manifesto.
Biological Bulletin, 215(3), 216–242.
Vanhaudenhuyse, A., Noirhomme, Q., Tshibanda, L. J., Bruno, M. A., Boveroux, P.,
Schnakers, C., … Boly, M. (2010). Default network connectivity reflects the level
of consciousness in non-communicative brain-damaged patients. Brain, 133(Pt 1),
161–171. doi:10.1093/brain/awp313

MARTIN M. MONTI SHORT BIOGRAPHY
Martin M. Monti, PhD, (http://montilab.psych.ucla.edu/people/martinmonti/MartinMMonti_CV.pdf) is Assistant Professor in the Departments

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of Psychology and Neurosurgery at University of California, Los Angeles.
Having earned his doctoral degree at Princeton University, he moved to
the MRC Cognition and Brain Sciences Unit, in Cambridge, the United
Kingdom, to specialize on the study of the vegetative and minimally
conscious states. Since joining the faculty at UCLA in 2011, research in Dr.
Monti’s laboratory (http://montilab.psych.ucla.edu) has centered on two
main questions: (i) what mechanisms underlie the loss and recovery of consciousness after severe brain injury and (ii) what is the relationship (if any)
between language and thought. His work has been featured in numerous
international peer-reviewed journals including the New England Journal of
Medicine, Brain, the Proceedings of the National Academy of Science, PLoS
Computational Biology, and Psychological Science, among others. In 2013,
Dr. Monti led an expert neuroimaging assessment of the late, former Israeli
Prime Minister, Ariel Sharon. Research in Dr. Monti’s research is supported
in part by the James S. McDonnell Foundation “Scholar Award.”

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et al.
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Horwitz

Disorders of Consciousness

13

Dissociation and Dissociative Identity Disorder (DID) (Psychology), Rafaële
J. C. Huntjens and Martin J. Dorahy
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Rumination (Psychology), Edward R. Watkins
Emotion Regulation (Psychology), Paree Zarolia et al.



Disorders of Consciousness
MARTIN M. MONTI

Abstract
Disorders of consciousness are a spectrum of neurological disorders, encompassing coma, the vegetative state, and the minimally conscious state, in which
patients acquire or develop an impairment of the two cardinal elements of
consciousness–wakefulness and awareness. One of the main sources of complexity
in this context is how to recognize and tell apart patients who retain some level of
awareness from patients who do not. Indeed, in the absence of any direct means
of assessing one’s level of awareness, we are forced to indirectly infer a patient’s
state on the basis of their ability to perform behaviors that, appearing clearly
voluntary, imply the presence of consciousness. In this contribution, we explore
recent evidence showing how brain imaging can be harnessed to address the
problem of consciousness in patients surviving severe brain injury. First, we focus
on recent experiments demonstrating how neuroimaging can be used to detect the
presence of voluntary “brain behavior” in otherwise non responsive patients, and to
allow a rudimentary form of non muscle-dependent communication strategy based
solely on voluntary brain activity. Second, we discuss recent findings concerning
network activity at different levels of awareness, and the relationship between
thalamo cortical circuits and consciousness.

INTRODUCTION
Disorders of consciousness (DOC) are a spectrum of disorders, typically
acquired or developed following severe brain injury, in which an individual’s consciousness is altered in a transient or permanent manner owing
to severe brain injury (Monti, 2012). In this context, consciousness is (simplistically) conceived as encompassing two cardinal elements (Laureys,
2005): wakefulness and awareness. Wakefulness refers to the level of one’s
consciousness and includes states such as deep sleep, drowsiness, and full
(normal) wake. Awareness refers to the content of consciousness, a more
elusive concept relating to the degree to which an individual possesses
subjective experience (of him/herself or the surrounding environment). In
daily life, most people experience the two elements of consciousness as being
intimately tied to each other. When asleep, for example, wakefulness and
awareness are both very low and jointly return as we progress through light
Emerging Trends in the Social and Behavioral Sciences. Edited by Robert Scott and Stephen Kosslyn.
© 2015 John Wiley & Sons, Inc. ISBN 978-1-118-90077-2.

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sleep and drowsiness toward awakening. In some circumstances, however,
these two elements dissociate from each other. During dream sleep, for
example, we commonly experience the presence of some level of (self)
awareness despite the absence of wakefulness. In DOC, we are typically
confronted with the reverse dissociation: wakefulness in the absence of (self)
awareness.
FOUNDATIONAL RESEARCH
DEFINITIONS
Coma. Coma is a state in which patients appear to lack both elements of
consciousness–they do not open their eyes even when intensely stimulated
(i.e., they have low level of consciousness) and they do not show any evidence
of awareness of themselves or of their surroundings [i.e., they have low, or
no, content of consciousness; (Monti, Laureys, & Owen, 2010)]. This state can
last from 2 to 4 weeks, with chronic coma being a rare long-term outcome.
Vegetative State (VS). While many coma patients recover within a few weeks,
a subset go on to regain some level of consciousness (i.e., “awaken” from
coma) but without regaining any content of consciousness (Monti, Laureys,
et al., 2010). This condition of “wakefulness in the absence of awareness”
defines the vegetative state (VS) (The Multi-Society Task Force on PVS,
1994). VS patients appear to periodically awaken and fall asleep, as indexed
by alternating periods of sustained eye-opening and eye-closing, but never
show any sign of purposeful behavior or (self) awareness. When this
condition lasts longer than 3 weeks, it is referred to as a persistent VS, after
which the chances of recovery decrease with time. If this condition lasts for
longer than 3 months1 (for patients who suffered from a nontraumatic brain
injury; e.g., anoxia) or 1 year (for patients who suffered from a traumatic
brain injury), a prognosis of permanent VS is made, after which chances of
recovery are typically considered to be minimal.
Until recently, the VS was believed to be a condition in which basic
vegetative nervous functions (including thermoregulation, respiration, and
sleep-wake cycles) are preserved, but in the complete absence of sensation or
thought–a view that is well captured by the term apallic syndrome (from the
Latin word a-pallium, “without a cortex”), sometimes used to describe these
patients. However, taking stock of about 15 years of neuroimaging research
in this cohort, employing tools such as positron emission tomography (PET),
functional magnetic resonance imaging (fMRI), and electroencephalography
1. In the United Kingdom, the threshold for a VS to be considered permanent after nontraumatic insult
is set at 6 months.

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(EEG), it has become increasingly clear that several aspects of cortical
function, including somatosensory (Boly et al., 2008), nociceptive (Laureys
et al., 2002), auditory (Kotchoubey et al., 2005), and semantic (Schnakers
et al., 2008) processing, among others, can remain even in the absence of
consciousness [see Monti (2012) for a recent comprehensive review].
Minimally Conscious State (MCS). Some patients remain in VS indefinitely.
Other patients, however, go on to regain some degree of awareness, thereby
progressing to a minimally conscious state (MCS) (Giacino et al., 2002). MCS
patients are defined as being awake and able to show, if intermittently, reproducible signs of (self) awareness in the form of purposeful (i.e., non reflexive)
behavior. An MCS patient, for example, might be able to demonstrate pursuit eye-movements toward salient stimuli in the environment, reaching for
objects, or even the production of (appropriate) vocalizations or gestures in
response to questions and commands. Minimally conscious patients might
remain in this condition indefinitely, or might further recover, emerging from
MCS, as they regain the ability to functionally/appropriately use objects or
accurately communicate (verbally or gesturally).
THE CONUNDRUM OF (FINDING) CONSCIOUSNESS
The definitions above, by which we differentially diagnose patients suffering
from DOCs, highlight one of the most crucial (and fascinating) questions in
this field: how can we tell if an individual, other than ourselves, is conscious?
Indeed, in the absence of a means to directly measure one’s consciousness,
the distinction between what most people would regard as “conscious” and
what most people would regard as “unconscious” relies on the pragmatic
principle by which the presence of voluntary (i.e., non reflexive) behavior
is taken to imply the presence of consciousness (Monti, Coleman, & Owen,
2009b). This principle of revealed consciousness is the bedrock upon which
current clinical assessments rely. If a patient can demonstrate any kind of
purposeful or voluntary behavior in response to stimulation (e.g., responding to a command such as “move your foot”), an MCS diagnosis is made.
Conversely, if a patient fails to demonstrate any sign of purposeful behavior,
a VS diagnosis is made. This reasoning, however, is logically flawed in that
it takes the absence of evidence of consciousness (e.g., absence of purposeful behavior) to be evidence of absence of consciousness (Monti et al., 2009b).
What if a patient were conscious but unable to perform any recognizably voluntary behavior due to motor impairment? What if a patient were conscious
but aphasic, and thus unable to make sense of a clinician’s request to perform
a certain behavior? What if a patient was conscious but did not possess sufficient residual cognitive functions to successfully comply with a clinician’s

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instruction? In all these cases, a patient would be diagnosed as being in VS,
despite retaining some level of (self) awareness. Confirming this view, several
studies, including retrospective audits (Andrews, Murphy, Munday, & Littlewood, 1996; Childs, Mercer, & Childs, 1993) and comparisons of diagnostic
methodologies (Schnakers et al., 2006, 2009), have reported a consistent 40%
misdiagnosis rate by which (minimally) conscious patients are incorrectly
considered to be unconscious (i.e., vegetative). While a number of different
causes might underlie the totality of these cases (e.g., lack of skill or training in specific clinical assessments, limited knowledge of this relatively rare
condition, and confusion in terminology), the presence of sensory and motor
impairment are well known to potentially mask the presence of consciousness by virtue of rendering the patient unable to either understand or comply
with a clinician’s attempt to elicit purposeful behavior (Monti, Laureys, et al.,
2010). In what follows, I will briefly cover the two main approaches that,
today, are being developed in order to overcome this “conundrum” of consciousness (Owen & Coleman, 2008).
CUTTING-EDGE RESEARCH
COGITO ERGO SUM BY NEUROIMAGING2
In 2006, a radical idea was introduced in the field as a potential solution to the
conundrum of consciousness (Owen et al., 2006). If some patients are (at least
minimally) conscious, but unable to produce overt behavior because of motor
impairments, maybe they might be able to engage in some form of recognizably voluntary “mental behavior” detectable through modern neuroimaging
techniques, thereby revealing a state of consciousness (Monti & Owen, 2010).
Consistent with this intuition, a number of patients who appeared behaviorally unresponsive in standard (behavior-based) clinical assessments were
shown to be able to willfully engage in a motor and a spatial mental imagery
task (i.e., imagining playing tennis and imagining walking in a familiar environment), eliciting the same neural substrate that is typically seen in healthy
individuals engaging in the same task, and thereby signaling a state of consciousness (Monti, Vanhaudenhuyse, et al., 2010; Owen, et al., 2006).
If a patient can engage at will in (at least) two mental tasks that can be distinguished from each other on the basis of neural activity, this ability can be
harnessed into a basic non motor-dependent communication strategy: a “language” made of any two possible alternatives (e.g., “yes/no” and “on/off”).
In agreement with this intuition, a patient who was initially believed to be in
a permanent VS was recently shown to be able to respond to autobiographical questions by engaging in one kind of imagery (e.g., playing tennis) to
2. Ropper (2010).

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convey an affirmative answer and in a different kind of imagery (e.g., walking around his home) to convey a negative answer (Monti, Vanhaudenhuyse,
et al., 2010). This finding was recently confirmed when a VS and an MCS
patients were shown to be able to use selective attention (i.e., the process
of focusing on a relevant stimulus while attempting to filter out irrelevant
ones) to respond to binary questions (Naci & Owen, 2013). This new procedure takes the approach presented in Monti, Vanhaudenhuyse, et al. (2010)
one step further by granting patients the ability to choose from a number of
potential answers rather than constraining them to two alternatives only. In
this novel procedure, patients are not asked to elicit different mental states
to give a positive or negative answer, but rather are presented aurally with
a number of possible answers (e.g., “yes, no, one, two, three, … ”) and then
asked to covertly count the number of times the answer they want to convey
is repeated. The timing of the observed brain activations can then be used to
infer which word (i.e., answer) a patient was focusing on.
Amidst these groundbreaking results, however, it is important to consider
that the dissociation between motor and brain responsiveness can go both
ways. As discussed above, some patients who appear unresponsive in
clinical (motor-based) assessments can appear responsive in neuroimaging
(brain-based) assessments. Conversely, some patients who appear responsive in clinical assessments can appear unresponsive in neuroimaging
tests–despite being able to verbally report that they were engaging in the
mental activity as instructed (Bardin et al., 2011), highlighting the complexities of interpreting negative findings in neuroimaging, and the need to
integrate standard and neuroimaging assessments (Monti, 2013).
TOWARD A NEUROPHYSIOLOGY OF DOC
Despite the flourishing of research in this field, we still have a very limited understanding of the physiological mechanisms underlying the loss and
(sometimes) recovery of consciousness after severe brain injury. In particular,
it is unclear why patients in a VS can retain several degrees of cortical activity
while failing to experience the feeling of (self) awareness.
Until recently, a prominent view held that VS patients only maintained
residual information processing in primary sensory cortices (Boly et al., 2004;
Laureys et al., 2002) without it propagating to higher-level and polimodal
integration areas that are considered necessary for conscious experience
(Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006). The evidence
available to date, however, does not seem to support this idea. Indeed,
neuroimaging studies have now amply shown that VS patients can exhibit
information processing outside primary cortices. A recent set of studies,
however, might suggest a different hypothesis accounting for the presence

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of extensive cortical processing in the absence of consciousness. Under this
view, the VS might best be characterized as a “disconnection syndrome”
(Laureys, 2005; Schiff, 2010) whereby residual brain processing in VS
patients might reflect isolated cognitive modules that, in the absence of
global integration, do not generate conscious experience (Monti, 2012).
Loss of Connectivity in DOC. Taking advantage of non invasive neuroimaging (and particularly task-free, or “rest,” approaches) a growing amount of
evidence suggests that DOC are characterized by a decrease in connectivity across frontal, parietal and temporo parietal regions. Specifically, a set of
regions often referred to as the default mode network, show decreased connectivity in proportion to the severity of the impairment of consciousness (Vanhaudenhuyse et al., 2010). Similarly, it has also been shown that minimally
conscious and VS patients differ significantly in the extent of “top-down”
connectivity extending from prefrontal cortex to superior temporal regions
(Boly et al., 2011), with the latter group of patients exhibiting a marked reduction. Assessing cortico cortical correlations and directional connectivity, however, does not bear much explanatory power vis-à-vis the question of why
they are so important for the maintenance (or generation) of consciousness.
To start addressing this question, and converge toward a more mechanistic understanding of the relationship between brain function and consciousness, a recent study investigated the effect of anesthetic agents on the network properties of the brain (Monti, Lutkenhoff, et al., 2013). Specifically, a
set of healthy volunteers underwent a resting state fMRI recording at different levels of consciousness: awake, sedated, unconscious, and recovery
(i.e., after having regained consciousness). Unlike the previous connectivity
studies, however, brain function was not assessed on the basis of the intensity of point-to-point correlations, but rather using tools derived from a relatively recent branch of mathematics—graph theory—which allows assessing
the brain as a network of nodes exchanging information (within the boundaries of the resolution offered by fMRI). In this study, the only unambiguous
signature of a state of unconsciousness, with respect to how information is
exchanged in brain networks, was a marked decrease in global efficiency. In
other words, the unconscious (healthy) brain suffers from a global decrease
in the efficiency with which information from distant parts of the brain can
be integrated. One intriguing aspect of this finding, which is awaiting replication in patients, is that consciousness might best be thought of as a how
(i.e., a mode of brain functioning) rather than a where–an idea that matches
the view proposed by a prominent theory of consciousness [i.e., Integrated
Information Theory of Consciousness; (Tononi, 2008)].

Disorders of Consciousness

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Thalamo-cortical Circuits in DOC. If indeed the loss of consciousness is related
to a loss of global information integration across distant regions of cortex,
the next step requires understanding the causes leading to these changes in
brain function. In general, thalamus has always been considered important
for the maintenance of consciousness. Indeed, post-mortem and neuroimaging examinations have revealed severe tissue death in thalamus (and hippocampus; (Adams, Graham, & Jennett, 2000)), as well as structural damage
in sub cortical white matter (Fernandez-Espejo et al., 2011), in this cohort of
patients. Today, a number of experiments seem to indicate that specific cortico subcortical circuits—uniting, among other regions, frontal and parietal
cortices, and medio dorsal thalamus–might be crucial to the integration of
information across distant loci of cortex (Schiff, 2010). Indeed, a recent study
has shown that, in acute severely injured patients, the degree of secondary,
non mechanical, damage to thalamus, and consequential atrophy in the anterior and dorso-medial areas occurring over the first 6 months post injury, is
predictive of chronic outcome (Lutkenhoff et al., 2013). Consistent with this
finding, chronic DOC patients have been shown to have, as a group, atrophy
along the medio dorsal axis of thalamus, when compared to healthy volunteers (Fernández-Espejo et al., 2010). Although this latter study reported no
differences between conscious (i.e., MCS) and unconscious (i.e., VS) patients,
the findings are consistent with the data observed in the acute setting. Finally,
the view that thalamo cortical circuits play a key role in DOCs is also consistent with a number of case studies. First, a patient was shown to specifically
recover thalamo frontal connectivity in concurrence with the reemergence
of consciousness (Laureys et al., 2000). Second, deep brain stimulation to the
antero medial regions of thalamus have been shown to have beneficial effects
in terms of improved responsiveness in DOC patients (Schiff et al., 2007).
Finally, it was recently shown that a patient with disrupted thalamo cortical connection was in a state of un consciousness despite the preservation of
cortico cortical (i.e., “default mode network”) connectivity (Boly et al., 2009),
thus potentially carving out very different roles, in the generation of consciousness, for thalamo cortical versus cortico cortical circuits.
KEY ISSUES FOR FUTURE RESEARCH
WHAT IS IT LIKE TO BE IN A VEGETATIVE STATE?
One issue that is still to be clarified is “what is it like” to be at the lower
boundaries of consciousness. More specifically, despite the flurry of recent
studies demonstrating the preservation of visual processing (Monti, Pickard,
& Owen, 2013), auditory and linguistic processing (Kotchoubey, et al., 2005),
attention (Monti, Coleman, & Owen, 2009a, Monti et al., in press), and even

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learning (Bekinschtein et al., 2009), it is unclear the degree to which mental life
can remain in DOC patients (Ropper, 2010), whether they can feel any pain
(Schnakers, Chatelle, Demertzi, Majerus, & Laureys, 2012; Schnakers et al.,
2010), or form lasting memories.
HARNESSING BCI FOR COMMUNICATION IN NON RESPONSIVE PATIENTS
A significant portion of the research described above shows that some
DOC patients can retain (a varying level of) (self) awareness even if behaviorally unresponsive. It is therefore important, for these cases, to develop
methods that might, through training algorithms, harness computers as
“brain-computer-interfaces” (BCI) that can be used for nonbehavioral
patients to interact with their environment (Naci et al., 2012).
THE TREATMENT GAP
One notable issue, in the context of DOCs, is that despite our increasing
sophistication in estimating the level of residual cognition and awareness
that might be retained after severe brain injury, there is today no standard
treatment available for these patients [there is, however, very exciting evidence that administration of amantadine accelerates the pace of functional
recovery in some post-traumatic DOC patients (Giacino et al., 2012)].
FROM NEUROSCIENCE TO CLINICAL PRACTICE, LAW, AND ETHICS
Finally, it is worth considering that our theoretical and practical advances
in this field bear repercussions outside the domain of science (Monti, 2013).
First, what is now considered science is still in search of a practical role in
medical care–a transformation that will require studies with much larger
samples than those typically carried out today. Second, an increased effort
in understanding the degree of mental life and cognitive processing possible
in minimally responsive individuals is necessary to allow a substantial discussion concerning which rights–if any, should be recognized to the patients
with respect to their participation in the medical decision making process
and, ultimately, self-determination (Peterson et al., 2013).
REFERENCES
Adams, J. H., Graham, D. I., & Jennett, B. (2000). The neuropathology of the vegetative state after an acute brain insult. Brain, 123(Pt 7), 1327–1338.
Andrews, K., Murphy, L., Munday, R., & Littlewood, C. (1996). Misdiagnosis of
the vegetative state: Retrospective study in a rehabilitation unit. BMJ, 313(7048),
13–16.

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Bardin, J. C., Fins, J. J., Katz, D. I., Hersh, J., Heier, L. A., Tabelow, K., … Voss,
H. U. (2011). Dissociations between behavioural and functional magnetic resonance imaging-based evaluations of cognitive function after brain injury. Brain,
134(Pt 3), 769–782. doi:10.1093/brain/awr005
Bekinschtein, T. A., Shalom, D. E., Forcato, C., Herrera, M., Coleman, M. R., Manes,
F. F., & Sigman, M. (2009). Classical conditioning in the vegetative and minimally
conscious state. Nature Neuroscience, 12(10), 1343–1349. doi:10.1038/nn.2391
Boly, M., Faymonville, M. E., Peigneux, P., Lambermont, B., Damas, P., Del Fiore,
G., … Laureys, S. (2004). Auditory processing in severely brain injured patients:
Differences between the minimally conscious state and the persistent vegetative
state. Archives of Neurology, 61(2), 233–238. doi:10.1001/archneur.61.2.233
Boly, M., Faymonville, M. E., Schnakers, C., Peigneux, P., Lambermont, B., Phillips,
C., … Laureys, S. (2008). Perception of pain in the minimally conscious state
with PET activation: An observational study. Lancet Neurology, 7(11), 1013–1020.
doi:10.1016/S1474-4422(08)70219-9
Boly, M., Garrido, M. I., Gosseries, O., Bruno, M. A., Boveroux, P., Schnakers, C., …
Friston, K. (2011). Preserved feedforward but impaired top-down processes in the
vegetative state. Science, 332(6031), 858–862. doi:10.1126/science.1202043
Boly, M., Tshibanda, L., Vanhaudenhuyse, A., Noirhomme, Q., Schnakers, C.,
Ledoux, D., … Laureys, S. (2009). Functional connectivity in the default network
during resting state is preserved in a vegetative but not in a brain dead patient.
Human Brain Mapping, 30(8), 2393–2400. doi:10.1002/hbm.20672
Childs, N. L., Mercer, W. N., & Childs, H. W. (1993). Accuracy of diagnosis of persistent vegetative state. Neurology, 43(8), 1465–1467.
Dehaene, S., Changeux, J. P., Naccache, L., Sackur, J., & Sergent, C. (2006). Conscious,
preconscious, and subliminal processing: A testable taxonomy. Trends in Cognitive
Sciences, 10(5), 204–211.
Fernandez-Espejo, D., Bekinschtein, T., Monti, M. M., Pickard, J. D., Junque, C., Coleman, M. R., & Owen, A. M. (2011). Diffusion weighted imaging distinguishes the
vegetative state from the minimally conscious state. NeuroImage, 54(1), 103–112.
doi:10.1016/j.neuroimage.2010.08.035
Fernández-Espejo, D., Junque, C., Bernabeu, M., Roig-Rovira, T., Vendrell, P., & Mercader, J. M. (2010). Reductions of thalamic volume and regional shape changes in
the vegetative and the minimally conscious states. Journal of Neurotrauma, 27(7),
1187–1193.
Giacino, J. T., Ashwal, S., Childs, N., Cranford, R., Jennett, B., Katz, D. I., … Zasler,
N. D. (2002). The minimally conscious state: Definition and diagnostic criteria.
Neurology, 58(3), 349–353.
Giacino, J. T., Whyte, J., Bagiella, E., Kalmar, K., Childs, N., Khademi, A., … Sherer,
M. (2012). Placebo-controlled trial of amantadine for severe traumatic brain injury.
The New England Journal of Medicine, 366(9), 819–826. doi:10.1056/NEJMoa1102609
Kotchoubey, B., Lang, S., Mezger, G., Schmalohr, D., Schneck, M., Semmler, A., …
Birbaumer, N. (2005). Information processing in severe disorders of consciousness:
Vegetative state and minimally conscious state. Clinical Neurophysiology: Official

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Journal of the International Federation of Clinical Neurophysiology, 116(10), 2441–2453.
doi:10.1016/j.clinph.2005.03.028
Laureys, S. (2005). The neural correlate of (un)awareness: Lessons from the vegetative state. Trends in Cognitive Sciences, 9(12), 556–559. doi:10.1016/j.tics.2005.10.010
Laureys, S., Faymonville, M. E., Luxen, A., Lamy, M., Franck, G., & Maquet, P. (2000).
Restoration of thalamocortical connectivity after recovery from persistent vegetative state [Letter]. Lancet, 355(9217), 1790–1791.
Laureys, S., Faymonville, M. E., Peigneux, P., Damas, P., Lambermont, B., Del Fiore,
G., … Maquet, P. (2002). Cortical processing of noxious somatosensory stimuli in
the persistent vegetative state. NeuroImage, 17(2), 732–741.
Lutkenhoff, E. S., McArthur, D. L., Hua, X., Thompson, P. M., Vespa, P. M., & Monti,
M. M. (2013). Thalamic atrophy in antero-medial and dorsal nuclei correlates
with six-month outcome after severe brain injury. NeuroImage. Clinical, 3, 396–404.
doi:10.1016/j.nicl.2013.09.010
Monti, M. M. (2012). Cognition in the vegetative state. Annual Review of Clinical Psychology, 8, 431–454. doi:10.1146/annurev-clinpsy-032511-143050
Monti, M. M. (2013). Ethics, Neuroimaging and disorders of consciousness: What is
the question? AJOB Neuroscience, 4(4), 1–2.
Monti, M. M., Coleman, M. R., & Owen, A. M. (2009a). Executive functions in the
absence of behavior: Functional imaging of the minimally conscious state. Progress
in Brain Research, 177, 249–260. doi:10.1016/S0079-6123(09)17717-8
Monti, M. M., Coleman, M. R., & Owen, A. M. (2009b). Neuroimaging and the vegetative state: Resolving the behavioral assessment dilemma? Annals of the New York
Academy of Sciences, 1157, 81–89. doi:10.1111/j.1749-6632.2008.04121.x
Monti, M. M., Laureys, S., & Owen, A. M. (2010). The vegetative state. BMJ, 341,
c3765. doi:10.1136/bmj.c3765
Monti, M. M., Lutkenhoff, E. S., Rubinov, M., Boveroux, P., Vanhaudenhuyse, A.,
Gosseries, O., … Laureys, S. (2013). Dynamic change of global and local information processing in propofol-induced loss and recovery of consciousness. PLoS
Computational Biology, 9(10), e1003271. doi:10.1371/journal.pcbi.1003271
Monti, M. M., & Owen, A. M. (2010). Behavior in the brain using functional neuroimaging to assess residual cognition and awareness after severe brain injury.
Journal of Psychophysiology, 24(2), 76–82. doi:10.1027/0269-8803/A000016
Monti, M. M., Pickard, J. D., & Owen, A. M. (2013). Visual cognition in disorders
of consciousness: From V1 to top-down attention. Human Brain Mapping, 34(6),
1245–1253. doi:10.1002/hbm.21507
Monti, M. M., Rosenberg, M., Finoia, P., Kamau, E., Pickard, J. D., & Owen, A. M.
(in press). Thalamo-frontal connectivity mediates top-down cognitive functions
in disorders of consciousness. Neurology.
Monti, M. M., Vanhaudenhuyse, A., Coleman, M. R., Boly, M., Pickard, J. D.,
Tshibanda, L., … Laureys, S. (2010). Willful modulation of brain activity in
disorders of consciousness. The New England Journal of Medicine, 362(7), 579–589.
doi:10.1056/NEJMoa0905370
Naci, L., Monti, M. M., Cruse, D., Kubler, A., Sorger, B., Goebel, R., … Owen,
A. M. (2012). Brain-computer interfaces for communication with nonresponsive
patients. Annals of Neurology, 72(3), 312–323. doi:10.1002/ana.23656

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Naci, L., & Owen, A. M. (2013). Making every word count for nonresponsive patients.
JAMA Neurology, 70(10), 1235–1241. doi:10.1001/jamaneurol.2013.3686
Owen, A. M., & Coleman, M. R. (2008). Functional neuroimaging of the vegetative
state. Nature Reviews Neuroscience, 9(3), 235–243. doi:10.1038/nrn2330
Owen, A. M., Coleman, M. R., Boly, M., Davis, M. H., Laureys, S., & Pickard, J. D.
(2006). Detecting awareness in the vegetative state. Science, 313(5792), 1402.
Peterson, A., Naci, L., Weijer, C., Cruse, D., Fernández-Espejo, D., Graham, M., &
Owen, A. M. (2013). Assessing decision-making capacity in the behaviorally nonresponsive patient with residual covert awareness. AJOB Neuroscience, 4(4), 3–14.
Ropper, A. H. (2010). Cogito ergo sum by MRI. The New England Journal of Medicine,
362(7), 648–649. doi:10.1056/NEJMe0909667
Schiff, N. D. (2010). Recovery of consciousness after brain injury: A mesocircuit
hypothesis. Trends in Neurosciences, 33(1), 1–9. doi:10.1016/j.tins.2009.11.002
Schiff, N. D., Giacino, J. T., Kalmar, K., Victor, J. D., Baker, K., Gerber, M., … Rezai,
A. R. (2007). Behavioural improvements with thalamic stimulation after severe
traumatic brain injury. Nature, 448(7153), 600–603. doi:10.1038/nature06041
Schnakers, C., Chatelle, C., Demertzi, A., Majerus, S., & Laureys, S. (2012). What
about pain in disorders of consciousness? The AAPS Journal, 14(3), 437–444.
doi:10.1208/s12248-012-9346-5
Schnakers, C., Chatelle, C., Vanhaudenhuyse, A., Majerus, S., Ledoux, D., Boly, M.,
… Laureys, S. (2010). The nociception coma scale: A new tool to assess nociception
in disorders of consciousness. Pain, 148(2), 215–219. doi:10.1016/j.pain.2009.09.028
Schnakers, C., Giacino, J., Kalmar, K., Piret, S., Lopez, E., Boly, M., … Laureys, S.
(2006). Does the FOUR score correctly diagnose the vegetative and minimally conscious states? Annals of Neurology, 60(6), 744–745; author reply 745.
Schnakers, C., Perrin, F., Schabus, M., Majerus, S., Ledoux, D., Damas, P., … Laureys,
S. (2008). Voluntary brain processing in disorders of consciousness. Neurology,
71(20), 1614–1620. doi:10.1212/01.wnl.0000334754.15330.69
Schnakers, C., Vanhaudenhuyse, A., Giacino, J., Ventura, M., Boly, M., Majerus, S., …
Laureys, S. (2009). Diagnostic accuracy of the vegetative and minimally conscious
state: Clinical consensus versus standardized neurobehavioral assessment. BMC
Neurology, 9, 35. doi:10.1186/1471-2377-9-35
The Multi-Society Task Force on PVS (1994). Medical aspects of the persistent
vegetative state (1). The New England Journal of Medicine, 330(21), 1499–1508.
doi:10.1056/NEJM199405263302107
Tononi, G. (2008). Consciousness as integrated information: A provisional manifesto.
Biological Bulletin, 215(3), 216–242.
Vanhaudenhuyse, A., Noirhomme, Q., Tshibanda, L. J., Bruno, M. A., Boveroux, P.,
Schnakers, C., … Boly, M. (2010). Default network connectivity reflects the level
of consciousness in non-communicative brain-damaged patients. Brain, 133(Pt 1),
161–171. doi:10.1093/brain/awp313

MARTIN M. MONTI SHORT BIOGRAPHY
Martin M. Monti, PhD, (http://montilab.psych.ucla.edu/people/martinmonti/MartinMMonti_CV.pdf) is Assistant Professor in the Departments

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of Psychology and Neurosurgery at University of California, Los Angeles.
Having earned his doctoral degree at Princeton University, he moved to
the MRC Cognition and Brain Sciences Unit, in Cambridge, the United
Kingdom, to specialize on the study of the vegetative and minimally
conscious states. Since joining the faculty at UCLA in 2011, research in Dr.
Monti’s laboratory (http://montilab.psych.ucla.edu) has centered on two
main questions: (i) what mechanisms underlie the loss and recovery of consciousness after severe brain injury and (ii) what is the relationship (if any)
between language and thought. His work has been featured in numerous
international peer-reviewed journals including the New England Journal of
Medicine, Brain, the Proceedings of the National Academy of Science, PLoS
Computational Biology, and Psychological Science, among others. In 2013,
Dr. Monti led an expert neuroimaging assessment of the late, former Israeli
Prime Minister, Ariel Sharon. Research in Dr. Monti’s research is supported
in part by the James S. McDonnell Foundation “Scholar Award.”

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Disorders of Consciousness
MARTIN M. MONTI

Abstract
Disorders of consciousness are a spectrum of neurological disorders, encompassing coma, the vegetative state, and the minimally conscious state, in which
patients acquire or develop an impairment of the two cardinal elements of
consciousness–wakefulness and awareness. One of the main sources of complexity
in this context is how to recognize and tell apart patients who retain some level of
awareness from patients who do not. Indeed, in the absence of any direct means
of assessing one’s level of awareness, we are forced to indirectly infer a patient’s
state on the basis of their ability to perform behaviors that, appearing clearly
voluntary, imply the presence of consciousness. In this contribution, we explore
recent evidence showing how brain imaging can be harnessed to address the
problem of consciousness in patients surviving severe brain injury. First, we focus
on recent experiments demonstrating how neuroimaging can be used to detect the
presence of voluntary “brain behavior” in otherwise non responsive patients, and to
allow a rudimentary form of non muscle-dependent communication strategy based
solely on voluntary brain activity. Second, we discuss recent findings concerning
network activity at different levels of awareness, and the relationship between
thalamo cortical circuits and consciousness.

INTRODUCTION
Disorders of consciousness (DOC) are a spectrum of disorders, typically
acquired or developed following severe brain injury, in which an individual’s consciousness is altered in a transient or permanent manner owing
to severe brain injury (Monti, 2012). In this context, consciousness is (simplistically) conceived as encompassing two cardinal elements (Laureys,
2005): wakefulness and awareness. Wakefulness refers to the level of one’s
consciousness and includes states such as deep sleep, drowsiness, and full
(normal) wake. Awareness refers to the content of consciousness, a more
elusive concept relating to the degree to which an individual possesses
subjective experience (of him/herself or the surrounding environment). In
daily life, most people experience the two elements of consciousness as being
intimately tied to each other. When asleep, for example, wakefulness and
awareness are both very low and jointly return as we progress through light
Emerging Trends in the Social and Behavioral Sciences. Edited by Robert Scott and Stephen Kosslyn.
© 2015 John Wiley & Sons, Inc. ISBN 978-1-118-90077-2.

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sleep and drowsiness toward awakening. In some circumstances, however,
these two elements dissociate from each other. During dream sleep, for
example, we commonly experience the presence of some level of (self)
awareness despite the absence of wakefulness. In DOC, we are typically
confronted with the reverse dissociation: wakefulness in the absence of (self)
awareness.
FOUNDATIONAL RESEARCH
DEFINITIONS
Coma. Coma is a state in which patients appear to lack both elements of
consciousness–they do not open their eyes even when intensely stimulated
(i.e., they have low level of consciousness) and they do not show any evidence
of awareness of themselves or of their surroundings [i.e., they have low, or
no, content of consciousness; (Monti, Laureys, & Owen, 2010)]. This state can
last from 2 to 4 weeks, with chronic coma being a rare long-term outcome.
Vegetative State (VS). While many coma patients recover within a few weeks,
a subset go on to regain some level of consciousness (i.e., “awaken” from
coma) but without regaining any content of consciousness (Monti, Laureys,
et al., 2010). This condition of “wakefulness in the absence of awareness”
defines the vegetative state (VS) (The Multi-Society Task Force on PVS,
1994). VS patients appear to periodically awaken and fall asleep, as indexed
by alternating periods of sustained eye-opening and eye-closing, but never
show any sign of purposeful behavior or (self) awareness. When this
condition lasts longer than 3 weeks, it is referred to as a persistent VS, after
which the chances of recovery decrease with time. If this condition lasts for
longer than 3 months1 (for patients who suffered from a nontraumatic brain
injury; e.g., anoxia) or 1 year (for patients who suffered from a traumatic
brain injury), a prognosis of permanent VS is made, after which chances of
recovery are typically considered to be minimal.
Until recently, the VS was believed to be a condition in which basic
vegetative nervous functions (including thermoregulation, respiration, and
sleep-wake cycles) are preserved, but in the complete absence of sensation or
thought–a view that is well captured by the term apallic syndrome (from the
Latin word a-pallium, “without a cortex”), sometimes used to describe these
patients. However, taking stock of about 15 years of neuroimaging research
in this cohort, employing tools such as positron emission tomography (PET),
functional magnetic resonance imaging (fMRI), and electroencephalography
1. In the United Kingdom, the threshold for a VS to be considered permanent after nontraumatic insult
is set at 6 months.

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(EEG), it has become increasingly clear that several aspects of cortical
function, including somatosensory (Boly et al., 2008), nociceptive (Laureys
et al., 2002), auditory (Kotchoubey et al., 2005), and semantic (Schnakers
et al., 2008) processing, among others, can remain even in the absence of
consciousness [see Monti (2012) for a recent comprehensive review].
Minimally Conscious State (MCS). Some patients remain in VS indefinitely.
Other patients, however, go on to regain some degree of awareness, thereby
progressing to a minimally conscious state (MCS) (Giacino et al., 2002). MCS
patients are defined as being awake and able to show, if intermittently, reproducible signs of (self) awareness in the form of purposeful (i.e., non reflexive)
behavior. An MCS patient, for example, might be able to demonstrate pursuit eye-movements toward salient stimuli in the environment, reaching for
objects, or even the production of (appropriate) vocalizations or gestures in
response to questions and commands. Minimally conscious patients might
remain in this condition indefinitely, or might further recover, emerging from
MCS, as they regain the ability to functionally/appropriately use objects or
accurately communicate (verbally or gesturally).
THE CONUNDRUM OF (FINDING) CONSCIOUSNESS
The definitions above, by which we differentially diagnose patients suffering
from DOCs, highlight one of the most crucial (and fascinating) questions in
this field: how can we tell if an individual, other than ourselves, is conscious?
Indeed, in the absence of a means to directly measure one’s consciousness,
the distinction between what most people would regard as “conscious” and
what most people would regard as “unconscious” relies on the pragmatic
principle by which the presence of voluntary (i.e., non reflexive) behavior
is taken to imply the presence of consciousness (Monti, Coleman, & Owen,
2009b). This principle of revealed consciousness is the bedrock upon which
current clinical assessments rely. If a patient can demonstrate any kind of
purposeful or voluntary behavior in response to stimulation (e.g., responding to a command such as “move your foot”), an MCS diagnosis is made.
Conversely, if a patient fails to demonstrate any sign of purposeful behavior,
a VS diagnosis is made. This reasoning, however, is logically flawed in that
it takes the absence of evidence of consciousness (e.g., absence of purposeful behavior) to be evidence of absence of consciousness (Monti et al., 2009b).
What if a patient were conscious but unable to perform any recognizably voluntary behavior due to motor impairment? What if a patient were conscious
but aphasic, and thus unable to make sense of a clinician’s request to perform
a certain behavior? What if a patient was conscious but did not possess sufficient residual cognitive functions to successfully comply with a clinician’s

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instruction? In all these cases, a patient would be diagnosed as being in VS,
despite retaining some level of (self) awareness. Confirming this view, several
studies, including retrospective audits (Andrews, Murphy, Munday, & Littlewood, 1996; Childs, Mercer, & Childs, 1993) and comparisons of diagnostic
methodologies (Schnakers et al., 2006, 2009), have reported a consistent 40%
misdiagnosis rate by which (minimally) conscious patients are incorrectly
considered to be unconscious (i.e., vegetative). While a number of different
causes might underlie the totality of these cases (e.g., lack of skill or training in specific clinical assessments, limited knowledge of this relatively rare
condition, and confusion in terminology), the presence of sensory and motor
impairment are well known to potentially mask the presence of consciousness by virtue of rendering the patient unable to either understand or comply
with a clinician’s attempt to elicit purposeful behavior (Monti, Laureys, et al.,
2010). In what follows, I will briefly cover the two main approaches that,
today, are being developed in order to overcome this “conundrum” of consciousness (Owen & Coleman, 2008).
CUTTING-EDGE RESEARCH
COGITO ERGO SUM BY NEUROIMAGING2
In 2006, a radical idea was introduced in the field as a potential solution to the
conundrum of consciousness (Owen et al., 2006). If some patients are (at least
minimally) conscious, but unable to produce overt behavior because of motor
impairments, maybe they might be able to engage in some form of recognizably voluntary “mental behavior” detectable through modern neuroimaging
techniques, thereby revealing a state of consciousness (Monti & Owen, 2010).
Consistent with this intuition, a number of patients who appeared behaviorally unresponsive in standard (behavior-based) clinical assessments were
shown to be able to willfully engage in a motor and a spatial mental imagery
task (i.e., imagining playing tennis and imagining walking in a familiar environment), eliciting the same neural substrate that is typically seen in healthy
individuals engaging in the same task, and thereby signaling a state of consciousness (Monti, Vanhaudenhuyse, et al., 2010; Owen, et al., 2006).
If a patient can engage at will in (at least) two mental tasks that can be distinguished from each other on the basis of neural activity, this ability can be
harnessed into a basic non motor-dependent communication strategy: a “language” made of any two possible alternatives (e.g., “yes/no” and “on/off”).
In agreement with this intuition, a patient who was initially believed to be in
a permanent VS was recently shown to be able to respond to autobiographical questions by engaging in one kind of imagery (e.g., playing tennis) to
2. Ropper (2010).

Disorders of Consciousness

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convey an affirmative answer and in a different kind of imagery (e.g., walking around his home) to convey a negative answer (Monti, Vanhaudenhuyse,
et al., 2010). This finding was recently confirmed when a VS and an MCS
patients were shown to be able to use selective attention (i.e., the process
of focusing on a relevant stimulus while attempting to filter out irrelevant
ones) to respond to binary questions (Naci & Owen, 2013). This new procedure takes the approach presented in Monti, Vanhaudenhuyse, et al. (2010)
one step further by granting patients the ability to choose from a number of
potential answers rather than constraining them to two alternatives only. In
this novel procedure, patients are not asked to elicit different mental states
to give a positive or negative answer, but rather are presented aurally with
a number of possible answers (e.g., “yes, no, one, two, three, … ”) and then
asked to covertly count the number of times the answer they want to convey
is repeated. The timing of the observed brain activations can then be used to
infer which word (i.e., answer) a patient was focusing on.
Amidst these groundbreaking results, however, it is important to consider
that the dissociation between motor and brain responsiveness can go both
ways. As discussed above, some patients who appear unresponsive in
clinical (motor-based) assessments can appear responsive in neuroimaging
(brain-based) assessments. Conversely, some patients who appear responsive in clinical assessments can appear unresponsive in neuroimaging
tests–despite being able to verbally report that they were engaging in the
mental activity as instructed (Bardin et al., 2011), highlighting the complexities of interpreting negative findings in neuroimaging, and the need to
integrate standard and neuroimaging assessments (Monti, 2013).
TOWARD A NEUROPHYSIOLOGY OF DOC
Despite the flourishing of research in this field, we still have a very limited understanding of the physiological mechanisms underlying the loss and
(sometimes) recovery of consciousness after severe brain injury. In particular,
it is unclear why patients in a VS can retain several degrees of cortical activity
while failing to experience the feeling of (self) awareness.
Until recently, a prominent view held that VS patients only maintained
residual information processing in primary sensory cortices (Boly et al., 2004;
Laureys et al., 2002) without it propagating to higher-level and polimodal
integration areas that are considered necessary for conscious experience
(Dehaene, Changeux, Naccache, Sackur, & Sergent, 2006). The evidence
available to date, however, does not seem to support this idea. Indeed,
neuroimaging studies have now amply shown that VS patients can exhibit
information processing outside primary cortices. A recent set of studies,
however, might suggest a different hypothesis accounting for the presence

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of extensive cortical processing in the absence of consciousness. Under this
view, the VS might best be characterized as a “disconnection syndrome”
(Laureys, 2005; Schiff, 2010) whereby residual brain processing in VS
patients might reflect isolated cognitive modules that, in the absence of
global integration, do not generate conscious experience (Monti, 2012).
Loss of Connectivity in DOC. Taking advantage of non invasive neuroimaging (and particularly task-free, or “rest,” approaches) a growing amount of
evidence suggests that DOC are characterized by a decrease in connectivity across frontal, parietal and temporo parietal regions. Specifically, a set of
regions often referred to as the default mode network, show decreased connectivity in proportion to the severity of the impairment of consciousness (Vanhaudenhuyse et al., 2010). Similarly, it has also been shown that minimally
conscious and VS patients differ significantly in the extent of “top-down”
connectivity extending from prefrontal cortex to superior temporal regions
(Boly et al., 2011), with the latter group of patients exhibiting a marked reduction. Assessing cortico cortical correlations and directional connectivity, however, does not bear much explanatory power vis-à-vis the question of why
they are so important for the maintenance (or generation) of consciousness.
To start addressing this question, and converge toward a more mechanistic understanding of the relationship between brain function and consciousness, a recent study investigated the effect of anesthetic agents on the network properties of the brain (Monti, Lutkenhoff, et al., 2013). Specifically, a
set of healthy volunteers underwent a resting state fMRI recording at different levels of consciousness: awake, sedated, unconscious, and recovery
(i.e., after having regained consciousness). Unlike the previous connectivity
studies, however, brain function was not assessed on the basis of the intensity of point-to-point correlations, but rather using tools derived from a relatively recent branch of mathematics—graph theory—which allows assessing
the brain as a network of nodes exchanging information (within the boundaries of the resolution offered by fMRI). In this study, the only unambiguous
signature of a state of unconsciousness, with respect to how information is
exchanged in brain networks, was a marked decrease in global efficiency. In
other words, the unconscious (healthy) brain suffers from a global decrease
in the efficiency with which information from distant parts of the brain can
be integrated. One intriguing aspect of this finding, which is awaiting replication in patients, is that consciousness might best be thought of as a how
(i.e., a mode of brain functioning) rather than a where–an idea that matches
the view proposed by a prominent theory of consciousness [i.e., Integrated
Information Theory of Consciousness; (Tononi, 2008)].

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7

Thalamo-cortical Circuits in DOC. If indeed the loss of consciousness is related
to a loss of global information integration across distant regions of cortex,
the next step requires understanding the causes leading to these changes in
brain function. In general, thalamus has always been considered important
for the maintenance of consciousness. Indeed, post-mortem and neuroimaging examinations have revealed severe tissue death in thalamus (and hippocampus; (Adams, Graham, & Jennett, 2000)), as well as structural damage
in sub cortical white matter (Fernandez-Espejo et al., 2011), in this cohort of
patients. Today, a number of experiments seem to indicate that specific cortico subcortical circuits—uniting, among other regions, frontal and parietal
cortices, and medio dorsal thalamus–might be crucial to the integration of
information across distant loci of cortex (Schiff, 2010). Indeed, a recent study
has shown that, in acute severely injured patients, the degree of secondary,
non mechanical, damage to thalamus, and consequential atrophy in the anterior and dorso-medial areas occurring over the first 6 months post injury, is
predictive of chronic outcome (Lutkenhoff et al., 2013). Consistent with this
finding, chronic DOC patients have been shown to have, as a group, atrophy
along the medio dorsal axis of thalamus, when compared to healthy volunteers (Fernández-Espejo et al., 2010). Although this latter study reported no
differences between conscious (i.e., MCS) and unconscious (i.e., VS) patients,
the findings are consistent with the data observed in the acute setting. Finally,
the view that thalamo cortical circuits play a key role in DOCs is also consistent with a number of case studies. First, a patient was shown to specifically
recover thalamo frontal connectivity in concurrence with the reemergence
of consciousness (Laureys et al., 2000). Second, deep brain stimulation to the
antero medial regions of thalamus have been shown to have beneficial effects
in terms of improved responsiveness in DOC patients (Schiff et al., 2007).
Finally, it was recently shown that a patient with disrupted thalamo cortical connection was in a state of un consciousness despite the preservation of
cortico cortical (i.e., “default mode network”) connectivity (Boly et al., 2009),
thus potentially carving out very different roles, in the generation of consciousness, for thalamo cortical versus cortico cortical circuits.
KEY ISSUES FOR FUTURE RESEARCH
WHAT IS IT LIKE TO BE IN A VEGETATIVE STATE?
One issue that is still to be clarified is “what is it like” to be at the lower
boundaries of consciousness. More specifically, despite the flurry of recent
studies demonstrating the preservation of visual processing (Monti, Pickard,
& Owen, 2013), auditory and linguistic processing (Kotchoubey, et al., 2005),
attention (Monti, Coleman, & Owen, 2009a, Monti et al., in press), and even

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EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

learning (Bekinschtein et al., 2009), it is unclear the degree to which mental life
can remain in DOC patients (Ropper, 2010), whether they can feel any pain
(Schnakers, Chatelle, Demertzi, Majerus, & Laureys, 2012; Schnakers et al.,
2010), or form lasting memories.
HARNESSING BCI FOR COMMUNICATION IN NON RESPONSIVE PATIENTS
A significant portion of the research described above shows that some
DOC patients can retain (a varying level of) (self) awareness even if behaviorally unresponsive. It is therefore important, for these cases, to develop
methods that might, through training algorithms, harness computers as
“brain-computer-interfaces” (BCI) that can be used for nonbehavioral
patients to interact with their environment (Naci et al., 2012).
THE TREATMENT GAP
One notable issue, in the context of DOCs, is that despite our increasing
sophistication in estimating the level of residual cognition and awareness
that might be retained after severe brain injury, there is today no standard
treatment available for these patients [there is, however, very exciting evidence that administration of amantadine accelerates the pace of functional
recovery in some post-traumatic DOC patients (Giacino et al., 2012)].
FROM NEUROSCIENCE TO CLINICAL PRACTICE, LAW, AND ETHICS
Finally, it is worth considering that our theoretical and practical advances
in this field bear repercussions outside the domain of science (Monti, 2013).
First, what is now considered science is still in search of a practical role in
medical care–a transformation that will require studies with much larger
samples than those typically carried out today. Second, an increased effort
in understanding the degree of mental life and cognitive processing possible
in minimally responsive individuals is necessary to allow a substantial discussion concerning which rights–if any, should be recognized to the patients
with respect to their participation in the medical decision making process
and, ultimately, self-determination (Peterson et al., 2013).
REFERENCES
Adams, J. H., Graham, D. I., & Jennett, B. (2000). The neuropathology of the vegetative state after an acute brain insult. Brain, 123(Pt 7), 1327–1338.
Andrews, K., Murphy, L., Munday, R., & Littlewood, C. (1996). Misdiagnosis of
the vegetative state: Retrospective study in a rehabilitation unit. BMJ, 313(7048),
13–16.

Disorders of Consciousness

9

Bardin, J. C., Fins, J. J., Katz, D. I., Hersh, J., Heier, L. A., Tabelow, K., … Voss,
H. U. (2011). Dissociations between behavioural and functional magnetic resonance imaging-based evaluations of cognitive function after brain injury. Brain,
134(Pt 3), 769–782. doi:10.1093/brain/awr005
Bekinschtein, T. A., Shalom, D. E., Forcato, C., Herrera, M., Coleman, M. R., Manes,
F. F., & Sigman, M. (2009). Classical conditioning in the vegetative and minimally
conscious state. Nature Neuroscience, 12(10), 1343–1349. doi:10.1038/nn.2391
Boly, M., Faymonville, M. E., Peigneux, P., Lambermont, B., Damas, P., Del Fiore,
G., … Laureys, S. (2004). Auditory processing in severely brain injured patients:
Differences between the minimally conscious state and the persistent vegetative
state. Archives of Neurology, 61(2), 233–238. doi:10.1001/archneur.61.2.233
Boly, M., Faymonville, M. E., Schnakers, C., Peigneux, P., Lambermont, B., Phillips,
C., … Laureys, S. (2008). Perception of pain in the minimally conscious state
with PET activation: An observational study. Lancet Neurology, 7(11), 1013–1020.
doi:10.1016/S1474-4422(08)70219-9
Boly, M., Garrido, M. I., Gosseries, O., Bruno, M. A., Boveroux, P., Schnakers, C., …
Friston, K. (2011). Preserved feedforward but impaired top-down processes in the
vegetative state. Science, 332(6031), 858–862. doi:10.1126/science.1202043
Boly, M., Tshibanda, L., Vanhaudenhuyse, A., Noirhomme, Q., Schnakers, C.,
Ledoux, D., … Laureys, S. (2009). Functional connectivity in the default network
during resting state is preserved in a vegetative but not in a brain dead patient.
Human Brain Mapping, 30(8), 2393–2400. doi:10.1002/hbm.20672
Childs, N. L., Mercer, W. N., & Childs, H. W. (1993). Accuracy of diagnosis of persistent vegetative state. Neurology, 43(8), 1465–1467.
Dehaene, S., Changeux, J. P., Naccache, L., Sackur, J., & Sergent, C. (2006). Conscious,
preconscious, and subliminal processing: A testable taxonomy. Trends in Cognitive
Sciences, 10(5), 204–211.
Fernandez-Espejo, D., Bekinschtein, T., Monti, M. M., Pickard, J. D., Junque, C., Coleman, M. R., & Owen, A. M. (2011). Diffusion weighted imaging distinguishes the
vegetative state from the minimally conscious state. NeuroImage, 54(1), 103–112.
doi:10.1016/j.neuroimage.2010.08.035
Fernández-Espejo, D., Junque, C., Bernabeu, M., Roig-Rovira, T., Vendrell, P., & Mercader, J. M. (2010). Reductions of thalamic volume and regional shape changes in
the vegetative and the minimally conscious states. Journal of Neurotrauma, 27(7),
1187–1193.
Giacino, J. T., Ashwal, S., Childs, N., Cranford, R., Jennett, B., Katz, D. I., … Zasler,
N. D. (2002). The minimally conscious state: Definition and diagnostic criteria.
Neurology, 58(3), 349–353.
Giacino, J. T., Whyte, J., Bagiella, E., Kalmar, K., Childs, N., Khademi, A., … Sherer,
M. (2012). Placebo-controlled trial of amantadine for severe traumatic brain injury.
The New England Journal of Medicine, 366(9), 819–826. doi:10.1056/NEJMoa1102609
Kotchoubey, B., Lang, S., Mezger, G., Schmalohr, D., Schneck, M., Semmler, A., …
Birbaumer, N. (2005). Information processing in severe disorders of consciousness:
Vegetative state and minimally conscious state. Clinical Neurophysiology: Official

10

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

Journal of the International Federation of Clinical Neurophysiology, 116(10), 2441–2453.
doi:10.1016/j.clinph.2005.03.028
Laureys, S. (2005). The neural correlate of (un)awareness: Lessons from the vegetative state. Trends in Cognitive Sciences, 9(12), 556–559. doi:10.1016/j.tics.2005.10.010
Laureys, S., Faymonville, M. E., Luxen, A., Lamy, M., Franck, G., & Maquet, P. (2000).
Restoration of thalamocortical connectivity after recovery from persistent vegetative state [Letter]. Lancet, 355(9217), 1790–1791.
Laureys, S., Faymonville, M. E., Peigneux, P., Damas, P., Lambermont, B., Del Fiore,
G., … Maquet, P. (2002). Cortical processing of noxious somatosensory stimuli in
the persistent vegetative state. NeuroImage, 17(2), 732–741.
Lutkenhoff, E. S., McArthur, D. L., Hua, X., Thompson, P. M., Vespa, P. M., & Monti,
M. M. (2013). Thalamic atrophy in antero-medial and dorsal nuclei correlates
with six-month outcome after severe brain injury. NeuroImage. Clinical, 3, 396–404.
doi:10.1016/j.nicl.2013.09.010
Monti, M. M. (2012). Cognition in the vegetative state. Annual Review of Clinical Psychology, 8, 431–454. doi:10.1146/annurev-clinpsy-032511-143050
Monti, M. M. (2013). Ethics, Neuroimaging and disorders of consciousness: What is
the question? AJOB Neuroscience, 4(4), 1–2.
Monti, M. M., Coleman, M. R., & Owen, A. M. (2009a). Executive functions in the
absence of behavior: Functional imaging of the minimally conscious state. Progress
in Brain Research, 177, 249–260. doi:10.1016/S0079-6123(09)17717-8
Monti, M. M., Coleman, M. R., & Owen, A. M. (2009b). Neuroimaging and the vegetative state: Resolving the behavioral assessment dilemma? Annals of the New York
Academy of Sciences, 1157, 81–89. doi:10.1111/j.1749-6632.2008.04121.x
Monti, M. M., Laureys, S., & Owen, A. M. (2010). The vegetative state. BMJ, 341,
c3765. doi:10.1136/bmj.c3765
Monti, M. M., Lutkenhoff, E. S., Rubinov, M., Boveroux, P., Vanhaudenhuyse, A.,
Gosseries, O., … Laureys, S. (2013). Dynamic change of global and local information processing in propofol-induced loss and recovery of consciousness. PLoS
Computational Biology, 9(10), e1003271. doi:10.1371/journal.pcbi.1003271
Monti, M. M., & Owen, A. M. (2010). Behavior in the brain using functional neuroimaging to assess residual cognition and awareness after severe brain injury.
Journal of Psychophysiology, 24(2), 76–82. doi:10.1027/0269-8803/A000016
Monti, M. M., Pickard, J. D., & Owen, A. M. (2013). Visual cognition in disorders
of consciousness: From V1 to top-down attention. Human Brain Mapping, 34(6),
1245–1253. doi:10.1002/hbm.21507
Monti, M. M., Rosenberg, M., Finoia, P., Kamau, E., Pickard, J. D., & Owen, A. M.
(in press). Thalamo-frontal connectivity mediates top-down cognitive functions
in disorders of consciousness. Neurology.
Monti, M. M., Vanhaudenhuyse, A., Coleman, M. R., Boly, M., Pickard, J. D.,
Tshibanda, L., … Laureys, S. (2010). Willful modulation of brain activity in
disorders of consciousness. The New England Journal of Medicine, 362(7), 579–589.
doi:10.1056/NEJMoa0905370
Naci, L., Monti, M. M., Cruse, D., Kubler, A., Sorger, B., Goebel, R., … Owen,
A. M. (2012). Brain-computer interfaces for communication with nonresponsive
patients. Annals of Neurology, 72(3), 312–323. doi:10.1002/ana.23656

Disorders of Consciousness

11

Naci, L., & Owen, A. M. (2013). Making every word count for nonresponsive patients.
JAMA Neurology, 70(10), 1235–1241. doi:10.1001/jamaneurol.2013.3686
Owen, A. M., & Coleman, M. R. (2008). Functional neuroimaging of the vegetative
state. Nature Reviews Neuroscience, 9(3), 235–243. doi:10.1038/nrn2330
Owen, A. M., Coleman, M. R., Boly, M., Davis, M. H., Laureys, S., & Pickard, J. D.
(2006). Detecting awareness in the vegetative state. Science, 313(5792), 1402.
Peterson, A., Naci, L., Weijer, C., Cruse, D., Fernández-Espejo, D., Graham, M., &
Owen, A. M. (2013). Assessing decision-making capacity in the behaviorally nonresponsive patient with residual covert awareness. AJOB Neuroscience, 4(4), 3–14.
Ropper, A. H. (2010). Cogito ergo sum by MRI. The New England Journal of Medicine,
362(7), 648–649. doi:10.1056/NEJMe0909667
Schiff, N. D. (2010). Recovery of consciousness after brain injury: A mesocircuit
hypothesis. Trends in Neurosciences, 33(1), 1–9. doi:10.1016/j.tins.2009.11.002
Schiff, N. D., Giacino, J. T., Kalmar, K., Victor, J. D., Baker, K., Gerber, M., … Rezai,
A. R. (2007). Behavioural improvements with thalamic stimulation after severe
traumatic brain injury. Nature, 448(7153), 600–603. doi:10.1038/nature06041
Schnakers, C., Chatelle, C., Demertzi, A., Majerus, S., & Laureys, S. (2012). What
about pain in disorders of consciousness? The AAPS Journal, 14(3), 437–444.
doi:10.1208/s12248-012-9346-5
Schnakers, C., Chatelle, C., Vanhaudenhuyse, A., Majerus, S., Ledoux, D., Boly, M.,
… Laureys, S. (2010). The nociception coma scale: A new tool to assess nociception
in disorders of consciousness. Pain, 148(2), 215–219. doi:10.1016/j.pain.2009.09.028
Schnakers, C., Giacino, J., Kalmar, K., Piret, S., Lopez, E., Boly, M., … Laureys, S.
(2006). Does the FOUR score correctly diagnose the vegetative and minimally conscious states? Annals of Neurology, 60(6), 744–745; author reply 745.
Schnakers, C., Perrin, F., Schabus, M., Majerus, S., Ledoux, D., Damas, P., … Laureys,
S. (2008). Voluntary brain processing in disorders of consciousness. Neurology,
71(20), 1614–1620. doi:10.1212/01.wnl.0000334754.15330.69
Schnakers, C., Vanhaudenhuyse, A., Giacino, J., Ventura, M., Boly, M., Majerus, S., …
Laureys, S. (2009). Diagnostic accuracy of the vegetative and minimally conscious
state: Clinical consensus versus standardized neurobehavioral assessment. BMC
Neurology, 9, 35. doi:10.1186/1471-2377-9-35
The Multi-Society Task Force on PVS (1994). Medical aspects of the persistent
vegetative state (1). The New England Journal of Medicine, 330(21), 1499–1508.
doi:10.1056/NEJM199405263302107
Tononi, G. (2008). Consciousness as integrated information: A provisional manifesto.
Biological Bulletin, 215(3), 216–242.
Vanhaudenhuyse, A., Noirhomme, Q., Tshibanda, L. J., Bruno, M. A., Boveroux, P.,
Schnakers, C., … Boly, M. (2010). Default network connectivity reflects the level
of consciousness in non-communicative brain-damaged patients. Brain, 133(Pt 1),
161–171. doi:10.1093/brain/awp313

MARTIN M. MONTI SHORT BIOGRAPHY
Martin M. Monti, PhD, (http://montilab.psych.ucla.edu/people/martinmonti/MartinMMonti_CV.pdf) is Assistant Professor in the Departments

12

EMERGING TRENDS IN THE SOCIAL AND BEHAVIORAL SCIENCES

of Psychology and Neurosurgery at University of California, Los Angeles.
Having earned his doctoral degree at Princeton University, he moved to
the MRC Cognition and Brain Sciences Unit, in Cambridge, the United
Kingdom, to specialize on the study of the vegetative and minimally
conscious states. Since joining the faculty at UCLA in 2011, research in Dr.
Monti’s laboratory (http://montilab.psych.ucla.edu) has centered on two
main questions: (i) what mechanisms underlie the loss and recovery of consciousness after severe brain injury and (ii) what is the relationship (if any)
between language and thought. His work has been featured in numerous
international peer-reviewed journals including the New England Journal of
Medicine, Brain, the Proceedings of the National Academy of Science, PLoS
Computational Biology, and Psychological Science, among others. In 2013,
Dr. Monti led an expert neuroimaging assessment of the late, former Israeli
Prime Minister, Ariel Sharon. Research in Dr. Monti’s research is supported
in part by the James S. McDonnell Foundation “Scholar Award.”

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