Probing consciousness with event-related potentials in the vegetative state

Abstract

Objective: Probing consciousness in noncommunicating patients is a major medical and neuroscientific challenge. While standardized and expert behavioral assessment of patients constitutes a mandatory step, this clinical evaluation stage is often difficult and doubtful, and calls for complementary measures which may overcome its inherent limitations. Several functional brain imaging methods are currently being developed within this perspective, including fMRI and cognitive event-related potentials (ERPs). We recently designed an original rule extraction ERP test that is positive only in subjects who are conscious of the long-term regularity of auditory stimuli. Methods:In the present work, we report the results of this test in a population of 22 patients who met clinical criteria for vegetative state. Results:We identified 2 patients showing this neural signature of consciousness. Interestingly, these 2 patients showed unequivocal clinical signs of consciousness within the 3 to 4 days following ERP recording. Taken Evaluating abnormal states of consciousness may be extremely challenging when relying only on the clinical examination alone. EEG-based paradigms have many advantages over fMRI for monitoring patients with altered consciousness because of 1) the millisecond-range resolution, 2) the low cost and noninvasiveness, 3) the ability to monitor at the bedside, and 4) the possibility of designing dedicated systems for clinical use. Conclusions:We recently designed a new test of consciousness using high-density scalp EEG in an auditory odd-ball paradigm.1 This test capitalizes on 2 properties which are specific to conscious processing 2-4 : one has to be conscious of a mental representation to actively maintain it in working memory, and to use it strategically. Our test evaluates cerebral responses to violations of temporal regularities. Short-interval violations due to the unexpected occurrence of a single deviant sound among a repeated train of standard sounds led to an early and automatic response in auditory cortex, the mismatch negativity ERP component. Moreover, long-term violations, defined as the presentation of a rare and unexpected series of 5 sounds, led to a late and spatially distributed response that was present only when subjects were attentive and aware of the auditory rule and of its violations (P3b component). Our observations showed that this

Evidence for a hierarchy of predictions and prediction errors in human cortex

“…In that respect, our observations add to a growing number of dissociations of these two systems. Bekinschtein et al (11) demonstrated that the early MMN resists visual distraction and remains present in subjects who are not conscious of the rule linking the five successive tones as well as in patients with in coma and vegetative state (22), whereas none of these properties hold for the global P3b, which therefore seems to index a conscious process. Prior ERP and functional MRI evidence confirms that the superior temporal region can respond to novel stimuli that are subliminal and fail to be detected (23,24), whereas a much broader frontoparietal network, indexed by the P3b, underlies conscious detection (24)(25)(26).…”

Disorders of consciousness after acquired brain injury: the state of the science

“…A wide array of behavioural, pharmacological and other rehabilitation-oriented treatments are routinely administered in patients with DOCs, but few interventions have been rigorously shown to accelerate or enhance functional recovery, 148 owing in part to the logistical and methodological difficulties of conducting placebocontrolled trials in this population. 149 Here, we review the treatments used to enhance arousal level, drive, c ommunication ability, and executive control processes.…”

Probing consciousness in a sensory-disconnected paralyzed patient

“…This paradigm developed by our team is usually able to probe neural signature of conscious processing in patients [5,6,9] . However, in this case, the patient's deafness prevented a reliable interpretation of this negative result.…”

“…During the last decade, several cognitively active tasks have been developed in this perspective while recording brain activity with fMRI or bedside EEG. For instance, putative neural signatures of conscious processing have been identified by asking a patient to perform a mental imagery task [3,4] or an explicit mental counting of rare stimuli delivered among frequent ones [5,6] . However, each of this measures require the patient to receive and perceive task instructions.…”