Generation of rapid eye movements during paradoxical sleep in humans.

Although rapid eye movements (REMs) are a prom- inent feature of paradoxical sleep (PS), their origin and functional significance remain poorly understood in humans. In animals, including nonhuman primates, REMs during PS are closely related to the occurrence of the so-called PGO waves, i.e., prominent phasic ac- tivities recorded throughout the brain but predomi- nantly and most easily in the pons (P), the lateral geniculate bodies (G), and the occipital cortex (O). Therefore, and because the evolution of species is par- simonious, a plausible hypothesis would be that dur- ing PS in humans, REMs are generated by mechanisms similar to PGO waves. Using positron emission tomog- raphy and iterative cerebral blood flow measurements by H2 15 O infusions, we predicted that the brain regions where the PGO waves are the most easily recorded in animals would be differentially more active in PS than in wakefulness, in relation with the density of the REM production (i.e., we looked for the condition (PS versus wakefulness) by performance (REM density) interaction). Accordingly, we found a significant inter- action effect in the right geniculate body and in the primary occipital cortex. The result supports the hy- pothesis of the existence of processes similar to PGO waves in humans, responsible for REM generation. The interest in the presence of PGO waves in humans is outstanding because the cellular processes involved in, or triggered by, PGO waves might favor brain plas- ticity during PS. © 2001 Academic Press