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.
Rapid eye movement sleep for REM's improvement of memory pertains to learning of procedures—new ways of moving the body (such as trampoline jumping), and new techniques of problem solving. REM deprivation seemed to impair declarative (i.e., factual) memory only in more complex cases, such as memories of longer stories. REM sleep apparently counteracts attempts to suppress certain thoughts. According to the "dual-process hypothesis" of sleep and memory, the two major phases of sleep correspond to different types of memory. “Night half” studies have tested this hypothesis with memory tasks either begun before sleep and assessed in the middle of the night, or begun in