Brain mechanisms of sleep: contribution of neuroimaging techniques

Functional brain neuroimaging essentially relies on two basic principles: functional segregation and functional interaction. Recent studies of the functional segregation of the human brain during sleep, using positron emission tomography and statistical parametric mapping, indicate that human brain function is organized in a very specific way in each state of vigilance. During slow wave sleep, the most deactivated areas are the upper brainstem, thalamic nuclei and basal forebrain; deactivation of the basal ganglia is also seen. In the cortex, the least active areas are the associative cortices of the frontal and parietal cortex. The anatomical extent of this deactivation remains uncertain. In rapid eye movement (REM) sleep there is significant activation of the dorsal tegmentum of the ponto-mesencephalic region and the thalamic nuclei. Within the cortex, the limbic areas (amygdala, hippocampus, orbito-frontal cortex and anterior cingulate cortex) are activated. In contrast, the associative areas of the frontal and parietal cortices are less active than other parts of the brain. The functional interactions between the amygdala and the temporal cortex during REM sleep differ markedly from those during other states of vigilance, and there is also an inverse relationship between the activities of the primary and secondary visual areas.