[Neurophysiology of Brain Death and Differential Diagnosis]

Brain death is defined as the permanent, irreversible, and complete loss of brain function, including the cessation of involuntary activities necessary to sustain life. Brain death differs from the vegetative state (VS) and minimally conscious state (MCS). The VS is characterized by the complete absence of behavioral evidence of self or of environmental awareness; however, the capacity for spontaneous or stimulus-induced arousal is preserved, as evidenced by the presence of sleep-wake cycles. The MCS is characterized by inconsistent but clearly discernible behavioral evidence of consciousness and can be distinguished from coma and the VS by documented evidence of specific behavioral features not found in either of these conditions. Electrophysiological evaluations, including the assessment of the auditory brainstem response, somatosensory evoked potential, pain-related P250 components, and continuous electroencephalography frequency analysis expressed as a compressed spectral array, are useful for the differential assessment of resting brain function in patients in a VS or MCS.