Abstract Mkid 108

Neurophysiological research in animals has recently underlined the importance of distinguishing sequential from single REM episodes, suggesting a possible different functional role of these sub-species of REM sleep. In human beings it is not still clear how much time has to elapse between two sections of REM sleep before they are recognised as two separate REM episodes, and hence sequential rather than single REM episodes. To this end we analysed 76 PSG recordings from 29 healthy young subjects. On the basis of the distribution of inter-REM intervals in our sample, we empirically set a combining rule of 20 minutes to define a REM sleep cycle, and to distinguish single vs. sequential REM episodes. Out of 276 REM sleep episodes detected, 71.38% were defined as single REM and 28.62 % as sequential REM episodes. Sequential, like single, REM episodes were not prevalent in any particular sleep cycle or part of the night, even though the percentage of sequential REM episodes seems to be related to circadian REM sleep pressure. The authors point up the importance of investigating experimentally the functional significance of these two sub-species of REM sleep in humans.