Functional neuroanatomy underlying the clinical subcategorization of minimally conscious state patients

Patients in a minimally conscious state (MCS) show restricted signs of awareness but are unable to communicate. We assessed cerebral glucose metabolism in MCS patients and tested the hypothesis that this entity can be subcategorized into MCS- (i.e., patients only showing nonreflex behavior such as visual pursuit, localization of noxious stimulation and/or contingent behavior) and MCS+ (i.e., patients showing command following). Patterns of cerebral glucose metabolism were studied using [F-18]-fluorodeoxyglucose-PET in 39 healthy volunteers (aged 46 +/- A 18 years) and 27 MCS patients of whom 13 were MCS- (aged 49 +/- A 19 years; 4 traumatic; 21 +/- A 23 months post injury) and 14 MCS+ (aged 43 +/- A 19 years; 5 traumatic; 19 +/- A 26 months post injury). Results were thresholded for significance at false discovery rate corrected p < 0.05. We observed a metabolic impairment in a bilateral subcortical (thalamus and caudate) and cortical (fronto-temporo-parietal) network in nontraumatic and traumatic MCS patients. Compared to MCS-, patients in MCS+ showed higher cerebral metabolism in left-sided cortical areas encompassing the language network, premotor, presupplementary motor, and sensorimotor cortices. A functional connectivity study showed that Broca's region was disconnected from the rest of the language network, mesiofrontal and cerebellar areas in MCS- as compared to MCS+ patients. The proposed subcategorization of MCS based on the presence or absence of command following showed a different functional neuroanatomy. MCS- is characterized by preserved right hemispheric cortical metabolism interpreted as evidence of residual sensory consciousness. MCS+ patients showed preserved metabolism and functional connectivity in language networks arguably reflecting some additional higher order or extended consciousness albeit devoid of clinical verbal or nonverbal expression.