Accessing previous mental sleep experience in REM and NREM sleep

This study investigated the processes by which contents previously stored in memory are retrieved and inserted into mental sleep experience (MSE). MSE reports were collected from six subjects awakened three times on each of eight nights in two alternate sequences of awakenings (NREM-REM-NREM; REM-REM-REM). The occurrences of interrelations between contents of report pairs were scored using Clark's (1970) feature matching model. These were greater for same night pairs than for different night pairs, and did not differ with respect to sequence of awakenings or order of report pairs (first-second, second-third, first-third). Contents of previous MSEs, therefore, seem to be accessible in both sleep types for insertion into current MSE. The interrelated units were more frequently lexical than propositional, with more paradigmatic than syntagmatic relationships in report pairs from both sequences of awakenings. Thus, the re-elaboration of contents of previous MSEs seems to occur mainly at the level of single contents in both types of sleep, with similar modalities of processing.