Non-rapid eye movement sleep 3D maze. Participants were then trained in the maze for 4 hours and later, during the various sleep cycles of nonREM sleep, REM sleep and wakefulness, they were scanned twelve times using a PET scan during the night. The PET scan demonstrated a higher blood flow in the hippocampus during SWS/non-REM sleep due to the training from the previous day while the control group exhibited no increased blood flow and they had not received the training the prior day. The brain activity during sleep, according to this study, would show the events of the previous day do make a difference.
REM rebound of normal human sleep, experimenters started depriving test subjects of only REM sleep, to test its unique importance. Every time a subject's electroencephalogram and eye movements indicated the beginning of REM sleep, the experimenter would thoroughly wake them for several minutes. As this “dream deprivation” continued, tendency to initiate REM increased, and the subjects were woken up more and more times each night. The subjects became irritable, anxious, and hungry, and several left the study early. After five nights, the remaining subjects were allowed to sleep undisturbed, and showed a significant increase in percentage of sleep devoted to REM: from