Intrinsic Brain Activity in Altered States of Consciousness
Annals of the New York Academy of Sciences May 1, 2008 M. Boly, C. Phillips, L. Tshibanda et al. 396 citations
Spontaneous brain activity, measured during rest, has been proposed as a way to understand brain-behavior relationships, but its value is debated. This review argues that altered states of consciousness—such as sleep, anesthesia, coma, vegetative state, epileptic loss of consciousness, and somnambulism—offer a privileged way to study these links. Early PET studies showed that extremely low or high brain activity often accompanies unconsciousness, but this link is not absolute. Voxel-based analyses consistently found impaired associative frontoparieto-cingulate areas across altered states. Recent fMRI studies reveal structured slow neuronal oscillations and coherent BOLD patterns, especially in the default-mode network, even during unconsciousness. These patterns may reflect default brain connectivity that transcends consciousness, but their functional significance remains unclear.