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Research Article

Multiple Processes Strengthen Memory during Sleep


Steffen Gais ,

Department of Neuroendocrinology, University of Lübeck, Ratzeburger Allee 160, Hs. 23a, 23538 Lübeck, DE
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Jan Born

University of Lübeck, DE
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For decades, enhancement of memory consolidation by sleep was investigated using tasks of declarative memory. Kami and coworkers (1994) employed for the first time a nondeclarative visual discrimination task for the investigation of sleep related memory consolidation. Improvement in this task can be seen only following a consolidation period, hours after practice has ended. A series of experiments from different groups examined the influence of sleep and wakefulness on the consolidation process and showed a strong sleep-dependency of task improvement. Enhanced performance on such discrimination tasks was found to occur only after a two-step consolidation process, at first dependent on periods of slow-wave sleep (SWS) rich sleep and, in a later phase, on sleep with a high amount of rapid eye movement (REM) sleep. Other data speak also in favour of a multi-step consolidation hypothesis of sleep. Experiments in rats show that sleep containing specific sequences of SWS and REM sleep positively affects memory performance. Several electro-physiological, neuromodulatory, and neuroendocrine mechanisms related to different sleep stages appear to contribute to memory processing during sleep.
How to Cite: Gais, S. and Born, J., 2004. Multiple Processes Strengthen Memory during Sleep. Psychologica Belgica, 44(1-2), pp.105–120. DOI:
Published on 01 Jan 2004.
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