Abstract :
The sheer amount of different opinions about what consciousness is
highlights its multifaceted character. The clinical study of consciousness in
coma survivors provides unique opportunities, not only to better
comprehend normal conscious functions, but also to confront clinical and
medico-ethical challenges. For example, pain in vegetative
state/unresponsive wakefulness syndrome patients (VS/UWS; i.e. awaken,
but unconscious) and patients in minimally conscious states (MCS; awaken,
with fluctuating signs of awareness) cannot be communicated and needs to
be inferred. Behaviorally, we developed the Nociception Coma Scale, a
clinical tool which measures patients’ motor, verbal, visual, and facial
responsiveness to noxious stimulation. Importantly, the absence of proof of
a behavioral response cannot be taken as proof of absence of pain.
Functional neuroimaging studies show that patients in VS/UWS exhibit no
evidence of control-like brain activity, when painfully stimulated, in
contrast to patients in MCS. Similarly, the majority of clinicians ascribe
pain perception in MCS patients. Interestingly, their opinions appear less
congruent with regards to pain perception in VS/UWS patients, due to
personal and cultural differences. The imminent bias in clinical practice due
to personal beliefs becomes more ethically salient in complex clinical
scenarios, such as end-of-life decisions. Surveys among clinicians show
that the majority agrees with treatment withdrawal for VS/UWS, but fewer
respondents would do so for MCS patients. For the issue of pain in patients
with disorders of consciousness, the more the respondents ascribed pain
perception in these states the less they supported treatment withdraw from
these patients. Such medico-ethical controversies require an objective and
valid assessment of pain (and eventually of consciousness) in noncommunicating
patients.
Functional neuroimaging during “resting state” (eyes closed, no task
performance) is an ideal paradigm to investigate residual cognition in noncommunicating
patients, because it does not require sophisticated technical
support or subjective input on patients’ behalf. With the ultimate intention
to use this paradigm in patients, we first aimed to validate it in controls. We
initially found that, in controls, fMRI “resting state” activity correlated with
subjective reports of “external” (perception of the environment through the
senses) or “internal” awareness (self-related mental processes). Then, using
hypnosis, we showed that there was reduced fMRI connectivity in the
“external network”, reflecting decreased sensory awareness. When more
cerebral networks were tested, increased functional connectivity was
observed for most of the studied networks (except the visual). These results
indicate that resign state fMRI activity reflects, at least partially, ongoing
conscious cognition, which changes under different conditions. Using the
resting state paradigm in patients with disorders of consciousness, we
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showed intra- and inter-network connectivity breakdown in sensorysensorimotor
and “higher-order” networks, possibly accounting for
patients’ limited capacities for conscious cognition. We have further
observed positive correlation between the Nociception Coma Scale scores
and the pain-related (salience) network connectivity, potentially reflecting
nociception-related processes in these patients, measured in the absence of
an external stimulus.
These results highlight the utility of resting state analyses in clinical
settings, where short and simple setups are preferable to activation
protocols with somatosensory, visual, and auditory stimulation devices.
Especially for neuroimaging studies, it should be stressed that such
experimental investigations tackle the necessary conditions supporting
conscious processing. The sufficiency of the identified neural correlates
accounting for conscious awareness remains to be identified via dynamic
and causal information flow investigations. Importantly, the quest of
subjectivity in non-communicating patients can be better understood by
adopting an interdisciplinary biopsychosocial approach, combining basic
neuroscience (bio), psychological-cognitive-emotional processing (psycho),
and the influence of different socioeconomic, cultural, and technological
factors (social).
