Psychophysiological analysis of memory function during the sleep onset transition.

Abstract

This dissertation presents an examination of explicit and implicit memory for auditory stimuli presented immediately prior to sleep onset. The paper begins with a review and critical analysis of the research findings published in the areas of sleep and memory, event-related potentials and sleep, and event-related potentials and memory. In the present study, thirty undergraduate subjects (17 female and 13 male) were presented with auditory stimuli in an oddball paradigm (single-syllable concrete nouns and 50-msec 1000-Hz beeps in a 1:4 ratio) until sleep onset. They were allowed to accumulate either 30 seconds or 10 minutes of sleep, awakened, and tested for free recall and recognition memory for the meaningful stimuli. Results from event-related potentials recorded during the stimulus presentation phase supported the conclusion that subjects continued to process the meaningful stimuli until sleep onset. After 10 minutes of sleep, but not after 30 seconds of sleep, subjects had profound amnesia on free recall for stimuli presented in the four minute window prior to sleep onset. Increased beta EEG power during the sleep period correlated positively with recall of stimuli in the four minute window. In the 30 second condition (versus the 10 minute condition), subjects responded significantly faster in the recognition task to words correctly recognized. It is concluded that when allowed to sleep for 10 minutes, subjects evidenced a mixed anterograde and retrograde amnesia for auditory stimuli presented in the four minute window prior to sleep onset. The results are discussed in terms of stimulus encoding, memory consolidation, and information retrieval. It is hypothesized that during the sleep onset transition, explicit memory systems switch from processing new information, to becoming a dedicated system for reprocessing information presented during the presleep period. Suggestions are given for further research, including studies of various sleep-disordered populations and the use of modified protocols.