Effects of early and late nocturnal sleep on priming and spatial memory

A wordstem priming task (nondeclarative memory), and a mental spatial rotat ion task (declarative memory) were presented to subjects of an experimental "sleep" group (n = 11) and of a "wake" control group (n = 10). Repetition priming effects and recall of spatial memory were tested after 3-hr retenti on intervals, which followed learning and were placed either in the early o r in the late half of the night. Sleep group subjects slept during the rete ntion intervals while subjects of the wake group stayed awake. As expected, early retention sleep was dominated by slow wave sleep (SWS), whereas rapi d eye movement (REM) sleep prevailed during late retention sleep. After ear ly retention sleep, recall of spatial memory was superior to that after lat e retention sleep (p < 0.01), and also to that after retention intervals of wakefulness (p < 0.05). In contrast, priming was more effective after late than early retention sleep (p < 0.05). It appears that early sleep dominat ed by SWS facilitates consolidation of declarative memory whereas late slee p dominated by REM sleep facilitates consolidation of nondeclarative memory .