Slow Wave Sleep Mentation: A Comparison Between the First and the Second Sleep Cycle

S leep and dream psychophysiology has been dominated for many years and, under certain aspects still today, by strong bias which considered the dreamlike mental activity as a peculiar aspect of REM sleep. The discovery of the REM phase (1), which determined a change in sleep research, raised great expectations. Going by the results of the first experiments on REM sleep, Dement and Kleitmann (2) were sure they had found "an objective method for the study of dreaming". The excessive emphasis put on the role ascribed to REM sleep almost led to consider the remaining sleep phases not very notable. It is not a case that sleep stages 1,2,3 e 4, although being different, have been classified all negative (Non-REM) in comparison with the REM phase. From the point of view of psychical contents, NREM sleep has been considered an almost silent period for a long time. The first REM/NREM dichotomy was based on these convictions, too. Experimental research soon showed clearly that the dream phenomenon has a very wide place in sleep (3). However, the protocols collected after NREM awakenings were often short and fragmented and similar to reality-oriented thoughts. By using such observations, it seemed possible to blindly discriminate REM reports from NREM reports with sufficient accuracy (4). On the basis of these new data, an attempt was made in order to elaborate an alternative model, according to which it seemed legitimate to ascribe a dream-like character to REM mental activity, and a thought-like character to NREM mental activity (REM/NREM second dichotomy). This point of view also was soon questioned, Foulkes (5,6) and other research groups (7-10) emphasised that, although NREM reports were more thoughtlike in comparison with REM reports, also in NREM reports dream-like experiences prevailed. Later on it Slow Wave Sleep Mentation: A Comparison Between the First and the Second Sleep Cycle