Oscillatory changes in multiple unit activity during rapid eye movement sleep

Abstract

Multiple unit activity of the midbrain reticular formation and the hippocampus was studied in cats during the sleep-wake cycle, with particular emphasis on events occurring during rapid eye movement (REM) sleep. It was observed that most REM periods have a duration of between 2 and 8 min, and that during REM periods of 6 min or more there was a cyclic alternation between phasic REM and tonic REM. Such cyclicity was absent during REM sleep of less than 6 min. In addition, it was observed that although in general, multiple unit activity during phasic REM was higher than during tonic REM, in 31 REM periods of more than 6 min in duration, unit activity in the midbrain reticular formation and hippocampus was uncoupled. In other words, during tonic REM, hippocampal unit activity was high and reticular activity low, and vice versa during phasic REM. The same observation was made during amphetamine administration, with or without eye movements. It is suggested that in view of the lack of sensory input during REM sleep, these oscillatory and uncoupled levels of activity in different areas may represent and/or provide a kind of information processing activity during this phase of sleep. It is further suggested that REM sleep can no longer be considered a homogeneous period, because important differences exist between phasic and tonic REM sleep.