The thematic continuity of mental experiences in REM and NREM sleep

In this study the characteristics of interrelated contents in paired reports of mental sleep experience (MSE) were analyzed to obtain insight as to the functioning of processes by which contents previously stored in memory are retrieved and inserted into MSE in rapid eye movements (REM) and non-REM (NREM) sleep. Ten subjects were awakened 3 times on each of 4 nights after 3 min of NREM sleep (in stage II or III before the first REM), of the first phase of REM sleep, and again of NREM sleep (in stage II or III after the first REM). The contents of all possible pairings of reports were scored by using Clark's (1970) feature-matching model and compared with respect to the factors ‘night’ (same/different), ‘type of report pairs’ (1stNREM-REM/REM-2ndNREM/ 1stNREM-2ndNREM), ‘unit interrelated’ (lexical/propositional), ‘interrelationship’ (paradigmatic/syntagmatic). The occurrences of interrelations were greater for same night pairs than for different night pairs, but without significant differences between types of report pairs: these data provide support for the thematic continuity of MSE in both NREM and REM sleep. The units interrelated in pairs of reports were more frequent at a lexical than a propositional level, showing more paradigmatic than syntagmatic interrelationships: these data suggest that the re-elaboration of contents of previous MSEs occurs mainly at a lower level, and that the modality of processing previous contents by insertion into current MSE is similar in NREM and REM sleep. Overall, these results give some support to the hypothesis that in the two types of sleep the production system of MSE is the same and suggest that differences between REM and REM reports are due to a differentiated functioning of certain higher-level processes of this system.