Non-rapid Eye Movement Sleep - Slow-wave Sleep

Slow-wave Sleep

Slow-wave sleep (SWS) is made up of the deepest stage of NREM, and is often referred to as deep sleep.

The highest arousal thresholds (e.g. difficulty of awakening, such as by a sound of a particular volume) are observed in stage 3. A person will typically feel groggy when awoken from this stage, and indeed, cognitive tests administered after awakening from stage 3 indicate that mental performance is somewhat impaired for periods up to 30 minutes or so, relative to awakenings from other stages. This phenomenon has been called "sleep inertia."

After sleep deprivation there is usually a sharp rebound of SWS, suggesting there is a "need" for this stage.

Slow Wave Sleep (SWS) is a highly active state unlike a state of brain quiescence as previously thought. Brain imaging data has shown that during nonREM sleep the regional brain activity is influenced by the waking experience just passed.

A study was done involving an experimental and a control group to have them learn to navigate a 3D maze. The blood flow in the parahippocampas gyrus increased in conjunction with the individual's performance through the 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 PET 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 does make a difference. One theory suggests a model of Hippocampal-neocortical dialogue. "Two stages of hippocampal activity have been proposed, the first being the recording of the memory during waking and the second involving the playback of the memory during nonREM sleep. This process of reactivation of memory firing sequences is believed to gradually reinforce initially weak connections between neocortical sites allowing the original information to be activated in the cortex independently of the hippocampus, and thus ensuring refreshed encoding capacity of the hippocampus." Maquet concluded that the areas of the brain involved with information processing and memory have increased brain activity during the slow wave sleep period. Events experienced in the previous day have more efficient and clearer memory recall the next day thus indicating that the memory regions of the brain are activated during SWS/non-REM sleep instead of being dormant as previously thought.