Abstract
Sleep after learning has been shown to foster the consolidation of new memories. However, fundamental questions on the best timing of learning before night-time sleep persist. We tested the hypothesis that learning directly prior to night-time sleep compared to 7.5 hrs prior to night-time sleep provides better conditions for the consolidation of declarative and procedural memories. Fifty healthy female adolescents (aged 16–17 years) were trained on a declarative word-pair and a procedural finger-tapping task at 3 pm (afternoon group, n = 25) or at 9 pm (evening group, n = 25), followed by a sleep laboratory night. Retrieval was assessed 24 hours and 7 days after initial training. Subjects trained in the afternoon showed a significantly elevated retention rate of word-pairs compared to subjects trained in the evening after 24 hours, but not after 7 days. In contrast, off-line gains in finger-tapping performance were significantly higher in subjects trained in the evening compared to those trained in the afternoon after both retention intervals. The observed enhanced consolidation of procedural memories after training in the evening fits to current models of sleep-related memory consolidation. In contrast, the higher retention of declarative memories after encoding in the afternoon is surprising, appeared to be less robust and needs further investigation.
Highlights
Encoded memory traces have been shown to evolve in a critical time window after learning when they are still fragile and susceptible to disruptive stimulus interference [1]
Twentyfive subjects were trained at 3 PM, 25 subjects were trained at 9 PM, followed by a sleep laboratory night from 10.30 PM to 7.30 AM
Declarative Word-Pair Task To test declarative memory consolidation, a word-pair association task was used in an adapted version consisting of 46 semantically related word pairs [18]
Summary
Encoded memory traces have been shown to evolve in a critical time window after learning when they are still fragile and susceptible to disruptive stimulus interference [1]. Research indicates that periods of sleep occurring in this window can facilitate the process of memory consolidation (for review see [2]). It remains unclear whether the timing of learning prior to night-time sleep affects long-term memory consolidation [3]. This appears to be of particular relevance in adolescence since this developmental period is especially critical for learning [4,5]. According to the most widely accepted classification scheme, these activities can be attributed to two major memory systems, the declarative and the procedural memory system [7]
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