Variations in the 5-hydroxy-indoleacetic acid concentration in the cerebrospinal fluid during the sleep-wake cycle in man.

A variation in the ventricular fluid 5-HIAA concentration has been observed during the phases of the sleep-wake cycle in man. This variation affects the NREM phase, during which 5-HIAA increases markedly, rather than the waking state and the REM phase. The results are discussed in relation to the possible relevance of serotonin to the sleep mechanism.