Consciousness beyond unresponsiveness
After admission at the IRU for a multifocal brain injury of vascular
origin, the patient remained unresponsive for five weeks during which
repeated CRS-R examinations resulted in a VS/UWS diagnosis. According to
recent recommendations (Giacino et al. , 2018; Comanducci et
al. , 2020; Kondziella et al. , 2020), the patient underwent a
series of paraclinical exams, including visual and quantitative
assessment of the resting EEG background, multimodal EP and EMG to
explore sensory and motor pathways as well as ERP to investigate
residual cognitive functions. Finding a preserved EEG background or
evidence of late cognitive ERP, such as the late P3, would have provided
a specific indication of a condition of clinical-paraclinical
dissociation, such as those previously described as covert awareness
(Owen et al. , 2006), cognitive-motor dissociations (CMD) (Schiff,
2015), functional LIS (Giacino et al. , 2009), MCS* (Gosserieset al. , 2014), covert cortical processing (Edlow et al. ,
2021). However, this possibility was apparently inconsistent with the
finding of a severely disorganized EEG background and the absence of a
P3. The novelty of the present report is that these negative results
were followed by a deeper level of investigation, involving TMS-EEG and
eventually by a fMRI active paradigm. As described in a recent expert
review (Comanducci et al. , 2020), the rationale for such a
hierarchical evaluation is that while EEG and ERP can provide a specific
indication of preserved consciousness when they are positive, they are
inconclusive in case of a negative result due to their low sensitivity.
Indeed, a direct assessment of the complexity of causal interactions
within the thalamocortical system, revealed a preserved capacity for
consciousness according to published norms, i.e. complexity values that
are only found in conscious subjects (Casali et al. , 2013;
Sarasso et al. , 2015; Casarotto et al. , 2016; Sinitsynet al. , 2020). In the absence of behavioral responsiveness and
lack of communication, the question of what it means for a particular
patient to have high brain complexity is hard to resolve. In general,
inferring an actual instance of preserved experience is based on the
evidence that control subjects who show
PCImax>0.31 during unresponsiveness in
sleep or under ketamine anesthesia regularly report dream experiences
upon awakening. In the present case, two additional elements strongly
support this conclusion. The first element is the fMRI evidence that the
patient was able to engage in volitional activity in response to verbal
commands during periods of unresponsiveness. The second element is the
convergent evidence (bilateral mesial-frontal lesional pattern, abnormal
EEG frontal slowing, altered EEG frontal response to TMS, MEP and EMG
showing a severe disconnection along the central and peripheral motor
pathway) that unresponsiveness could be explained by a fundamental
impairment of executive/motor circuits and pathways, rather than by
unconsciousness.