부산대학교 도서관

Introduction : The hippocampus is critical for learning and consolidation of behaviourally-relevant spatial information. During spatial learning, spatially-related firing patterns of hippocampal place cells reflecting the subjects' location can be detected. It is widely acknowledged that the stabilization of newly encoded memory traces during active system consolidation is promoted by post-learning slow wave sleep (SWS). Here, hippocampal neural sequences are reactivated ("replay") accompanied by neocortical slow oscillations thereby synchronizing spindle-ripple events originating from hippocampal and thalamic regions. Studies in rodents and humans reported a facilitation of spatial memories after full nights of sleep, in particular in early sleep SWS (i.e., sharp-wave ripples and slow waves). In this ongoing study, we investigated the effect of a 90-min nap on sleep-associated memory consolidation of spatial information. The advantage of an isolated nap condition is the possibility to selectively study the effect of SWS on memory consolidation. Patients & Methods: Forty healthy students between 21 and 32 years were divided into a sleep group (24±1,64 years, 55% female) and a wake group (24±2,68 years, 55% female). For testing spatial learning, the Virtual Water Maze (VWM), a digitalised version of the established Morris Water Maze Test for hippocampus-dependent place learning was used. Here, students had to find a treasure box hidden in the same position on a virtual island. Between learning and the recall sessions of the VWM (90 minutes), students either performed a mid-day nap accompanied by polysomnography (sleep condition) or watched emotionally neutral documentaries (wake condition). The improvement in the recall session was then compared between the groups and the influence of EEG sleep measures was analysed. Results: We found a significant positive correlation between spatial memory consolidation and time spent in SWS (SWS [min]: r=0,612, p=0,004). Accordingly, there was a tendency of a stronger consolidation when amounts of slow oscillations and sleep spindles were higher. When directly compared, there was no significant difference in the various consolidation measures of VWM between the groups. Conclusion: We found that consolidation of hippocampus-dependent spatial memory in a young healthy population was related to longer time spent in SWS as well as the amount of sleep spindles and slow oscillations during NonREM sleep of a 90-minute nap. Our data support the notion that the efficacy of hippocampus-dependent spatial memory consolidation depends on the duration of SWS. [ABSTRACT FROM AUTHOR]