COORDINATED EXPRESSION IN CHRONICALLY UNCONSCIOUS PERSONS

The clinically described 'persistent vegetative state' (PVS), consists of wakefulness unaccompanied by any evidence of the subject's awarene ss of self or environment. Past studies from our own and other laborat ories have used positron emission tomography (PET) to study brain meta bolism in approximately 20 such patients during wakeful periods. All t hose efforts identified global cerebral glucose metabolism at or below levels encountered during deep barbiturate anaesthesia. Nevertheless, the clinical literature includes rare reports of relatively isolated cognitive functions expressed by PVS patients late in their course. Th e observation raises the question of whether such activity reflects aw areness or unconscious automatic behaviour. We employed magnetometry ( MEG), PET scanning, MR imaging and 24-hour EEG recordings to evaluate three patients clinically vegetative between six months and 20 years a fter onset. Neither meticulous clinical examinations nor 24-hour EEG a nd video monitoring provided any hint of cognitive interaction in any subject. Nevertheless, patient I uttered single words once every 48 ho urs or more; patient 2 frequently expressed coordinated, non-purposefu l, non-dystonic movements in arms and/ or legs; and, patient 3 express ed strong emotional negativity without motor responses to noxious stim uli with occasional quieting in response to prosodic stimuli. All pati ents had whole-brain averaged global metabolism levels below 50% of no rmal. Patient I, however, demonstrated preserved islands of increased metabolism in the posterior frontal and posterior temporal lobes, as w ell as MEG activations of Heschl's gyrus all located in the left hemis phere. In patient 2, selected increased metabolism was confined to the frontal poles and related subcortical structures. MRI in patient 3 de monstrated severe, bilateral post-traumatic cerebral atrophy. PET meta bolism was diffusely reduced to 40% of normal but MEG evoked potential s indicated early and late sensory processing with abnormal later evok ed components. The correlation of fragmentary behaviour with preserved metabolic and physiologic activity in cortical and subcortical region s known to support specific modular functions is novel. The finding de monstrates the capacity of severely damaged brains to partially expres s surviving modular functions without evidence of integrative processe s that would be necessary to produce consciousness. We conclude that t he mere expression of isolated neuropsychologic activity by isolated m odules is insufficient to generate consciousness in overwhelmingly dam aged brains.