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 whilst weaker, transient, "noise" memory traces disintegrate. Memory consolidation during paradoxical sleep is specifically correlated with the periods of rapid eye movement, which do not occur continuously. One explanation for this correlation is that the PGO electrical waves, which precede the eye movements, also influence memory. REM sleep could provide a unique opportunity for “unlearning” to occur in the basic neural networks involved in homeostasis, which are protected from this “synaptic downscaling” effect during deep sleep. REM sleep prevails most after birth, and diminishes with age. According to the "ontogenetic hypothesis", REM (also known in neonates as "active sleep") aids