For memory enhancement, the kind of sleep you get is important

Van Der Werf et al. have recorded electroencephalograms from people as they slept, setting off a beeping sound when the electroencephalograms were consistent with slow-wave (deeper) sleep, thus causing subjects to move into a shallower sleep stage without awakening. Although the total amount of sleep that subjects got was unchanged, these people did worse on a later test of scene recall than subjects who had slept normally. When the subjects were later scanned in a functional magnetic resonance imaging scanner, they also showed reduced hippocampal activation while they were encoding the to-be-remembered scenes. Thus the hippocampus appears to be particularly sensitive to shallow, but intact, sleep.