This paper presents an overview of the contribution of functional brai
n mapping to the study of human sleep, Early studies were essentially
successful in describing the variations of the global level of cerebra
l metabolism. More recently, regional distribution of cerebral blood f
low was reported. The results suggest that the permissive and executiv
e processes of slow wave sleep and REM sleep are similar in humans and
in animals. They also show cortical blood flow distributions specific
to each sleep stage. The cellular mechanisms underlying the involveme
nt of these cortical areas in sleep are not yet precisely known. They
should be looked for by further investigations in animals. Future rese
arch in functional neuroimaging will attempt to explore functional and
, hopefully, effective connectivity between cerebral areas involved in
sleep processes. This final goal will probably require the co-registr
ation of two or more brain imaging techniques to precisely describe th
e spatio-temporal course of neuronal interactions occurring during sle
ep.