le
s p
visually fixate or speak a word or gesture in response to a com-
perform these overt behaviors is often decoupled from conscious-
ness as a direct result of the brain injury. As a matter of fact, we can
never exclude the possibility of some form of consciousness in pa-
tients thought to be in VS with complete certainty.
In this issue of the journal, Cavinato and co-workers address the
question: Is there an electrophysiological marker, which differenti-
ates between MCS and VS? (see Cavinato et al., in this issue). Their
results add to the growing corpus of studies exploring the neural
first name” paradigm (patient’s own name as deviant and unfamil-
a reliable P300 component could be observed in all three condi-
tions. These findings corroborate earlier reports showing that
38% of patients in VS generate a P300 wave. Interestingly, patients
in MCS exhibit significantly longer P300 latencies for the ‘‘subject’s
own name” and the ‘‘other first name” paradigms than patients in
VS. This unexpected finding suggests that the cognitive processes
associated with the generation of a P300 wave in these paradigms,
such as attention, memory and language processing, differ
between individuals in VS and MCS. The authors emphasize that
Clinical Neurophysiology xxx (2010) xxx–xxx
lab
ro
.e lcorrelates of consciousness in individuals with VS and MCS. MCSmand. The diagnosis of MCS is difficult, time-consuming and falli-
ble, because there is no single clinical sign of awareness. Clinical
tests rely on a patient demonstrating awareness and cognitive
capabilities by means of overt motor actions, as does the Glasgow
Coma Score, which counts eye opening, as well as the best verbal
and motor responses (Teasdale and Jennett, 1974). The ability to
iar names as standard stimulus). These paradigms represent grow-
ing complexity and cognitive demand. To note, the authors
instructed their patients to count the occurrence of deviant stimuli
to better differentiate between patients in VS and MCS (similar to
the paradigm used by Schnakers et al., 2008). The study indicates
that in 6 out of 11 patients fulfilling the behavioral criteria for VSEditorial
The neural correlates of consciousness: E
and neuroimaging evidence for consciou
Consciousness is a puzzling phenomenon. We all know it, but
only from a subjective, first-person perspective. For centuries, phi-
losophers, psychologists and scientists have studied the content
and the physical basis of consciousness. Most researchers agree
that consciousness is not a dichotomic quality. There is convincing
evidence that consciousness comprises distinct states, such as con-
sciousness of pain, emotions or language. In addition, there is con-
vincing evidence that conscious experience and behavior is
associated with the integrity of specific neural circuits, i.e., the
neural correlates of consciousness (Metzinger, 2000). The exact
relationship between the subjective experience that constitutes
consciousness and these objective neurophysiological phenomena
is still unclear.
Disorders of consciousness attract growing attention. An
increasing number of individuals survive critical brain injury, some
with severe disorders of consciousness. For clinical diagnosis, dis-
orders of consciousness have been categorized in terms of aware-
ness and wakefulness (Gawryluk et al., 2010). Wakefulness refers
to a state in which individuals can open their eyes and exhibit
some degree of motor arousal. Awareness refers to a state in which
individuals have experiences of any kind, such as thoughts, mem-
ories, emotions and pain. Applying these qualities, three distinct
disorders of consciousness have been defined: coma (absence of
both wakefulness and awareness), persistent vegetative state
(VS; wakefulness without awareness) and locked-in syndrome
(wakefulness and awareness).
More recently, clinical experience motivated the definition of
another disorder of consciousness, the minimally conscious state
(MCS, Giacino et al., 2002). These individuals demonstrate wake-
fulness but, in contrast to patients in VS, inconsistent but discernible
evidence of awareness. Patients in MCS may reach for objects or
Contents lists avai
Clinical Neu
journal homepage: www1388-2457/$36.00  2010 International Federation of Clinical Neurophysiology. Publish
doi:10.1016/j.clinph.2010.10.024ctrophysiological
rocessing in vegetative state
patients with severe brain injury are frequently misdiagnosed as
being in VS. The accurate diagnosis of MCS as opposed to VS affects
important decisions concerning care and rehabilitation and is thus
of great clinical importance.
The authors use the P300 component to study cognitive pro-
cessing of information. The P300 wave, first reported 45 years
ago (Sutton et al., 1965), reflects neural networks that are engaged
in information processing, including attention and memory, and
are distributed throughout the cerebral cortex and thalamus. Elec-
trophysiological recordings have important advantages compared
to other approaches probing human brain function. They are rela-
tively easy to perform, portable and inexpensive. In addition, there
are standardized protocols for data acquisition and analysis (Dun-
can et al., 2009). Probably of greatest importance, electrophysio-
logical studies reveal the time course of brain activity related to
cognitive processing with high temporal resolution.
In an earlier study, the authors focused on the prediction of con-
sciousness recovery in patients with post-traumatic VS (Cavinato
et al., 2009). They used a classical two-stimulus oddball task to eli-
cit the P300 using the patient’s own name as deviant and a pure
tone as standard stimulus (‘‘subject’s own name” paradigm). There
is evidence that the amplitude of the P300 wave increases when
more salient stimuli are used, such as the own first name instead
of visual or auditory deviants. The authors found that P300 is a
strong predictor of future recovery of consciousness in VS. This
finding is in line with several studies that have confirmed the util-
ity of P300 evoked by deviant tones to predict awakening and
favourable outcome from coma and VS.
In the present study, Cavinato and co-workers continue using
the ‘‘subject’s own name” paradigm, but add a pure tone
(2000 Hz as deviant, 1000 Hz as standard stimulus) and an ‘‘other
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