There is a strongly held opinion that one of the mostimportant functions of sleep is its involvement in the for-mation of memories [8, 20, 21]. In the state of waking,learning occurs by means of encoding information followedby its consolidation [3, 8]. The term consolidation refers tothe processes transforming new, labile memory traces intostable long-term memories. Sleep is believed to promotethis process. Reports on the involvement of sleep in memo-ry consolidation have a long history [11] and remain underactive development [2, 8, 14, 20, 22, 26]. However, how theduration of sleep is related to its influences on memoryremains unknown. Sleep consisting of eight hours overnightand short periods (1–2 h) has been shown to have positiveinfluences [7, 17, 25], as has even transient (6–7 min) day-time sleep [12]; longer-lasting sleep appears to have a moremarked effect on memory [8, 22]. As regards the time inter-val between training and sleep, data have been reportedshowing that shorter intervals increase the influence ofsleep on the process of memory consolidation. For example,sleep 3 h after training was more effective for declarativememory than sleep at 10 h [10, 23]. However, the questionof the nature of the effects of different phases of sleep(slow-wave and paradoxical sleep) on different types ofmemory (declarative and procedural) remains controversial[7, 13, 17, 25].The standard test for studies of learning and memoryprocesses in animals is the Morris water test [15]. This testallows use of types of learning with different levels ofinvolvement of the hippocampus. Spatial hippocampus-dependent memory in animals is comparable with declara-tive memory in humans, while memory not dependent onthe hippocampus is comparable with procedural memory. Inthe Morris water test, the animal learns to avoid forcedswimming by finding a platform, which can be hiddenbeneath the surface or visible above the surface, placed inone of the four quadrants (termed the “target”). When theplatform is under water, learning is associated with remem-bering spatial relationships in the surrounding environment,