Behavioral and physiological correlates of brain serotoninergic unit activity.

Raphe unit activity in rats and cats displays a slow and regular discharge pattern across a variety of situations. The activity is, however, state-dependent, displaying a marked reduction during slow wave sleep and almost complete quiescence during REM sleep. Other than the level of synaptic serotonin, very little is known about the physiological variables affecting these neurons. Behaviorally, raphe neuron activity is correlated with arousal or tonic motor activity, and appears to be driven by phasic afferent input. It is hypothesized that these neurons exert a general modulatory role upon physiology and behavior.