Slow-wave Sleep - Discussion

Discussion

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

After sleep deprivation there is a sharp rebound of SWS, that is, the following bout of sleep will include more and deeper SWS than normal.The duration of slow-wave sleep is determined by the previous duration of this stage as well as the duration of prior wakefulness.

The major factor determining how much slow-wave sleep is observed in a given sleep period is the duration of preceding wakefulness, likely related to accumulation of sleep-promoting substances in the brain. Some of the few factors known to increase slow-wave sleep in the sleep period that follows them include body heating (as by immersion in a hot tub), high carbohydrate ingestion, and intense prolonged exercise. Studies have shown, slow-wave sleep is enabled when brain temperature surpasses a certain threshold. It is hypothesized that the threshold is regulated by circadian and homeostatic processes.

In addition to these factors, the duration of SWS periods can be increased by the ingestion of THC, certain SSRIs, and other antidepressants. In instances such as these, TST (Total Sleep Time) is often unaffected due to circadian rhythms and/or a person's alarm clock and early morning obligations. This increase of SWS can lead to increased REM latency and a decrease in REM period durations. If the total time spent in REM is decreased long enough and repeatedly over a substantial number of nights a "REM rebound" will occur in response to removal of its inhibitor. An increase in REM is believed to produce symptoms of depression and bipolar disorder in many patients for an amount of time relative to the severity of the previous "REM suppression." It is debatable whether or not this could explain the return in symptoms of depression disorder after removal of SSRI medications.

Certain substances, such as benzodiazepines (e.g. Ativan, Valium, Klonopin) seem to have the reverse effect on the time spent in SWS. Instead of lengthening SWS (as do the substances mentioned above), they are known to shorten the time. While these sedatives can increase sleep duration or shorten the time it takes before sleep-onset occurs, they tend to deprive patients of deep sleep.

The chemical gamma-Hydroxybutyric acid (GHB) is known to promote SWS. In the United States, the Food and Drug Administration permits the use of GHB under the trade name Xyrem to reduce cataplexy attacks and excessive daytime sleepiness in patients with narcolepsy.

Reduced slow wave sleep (SWS) may predict high blood pressure in older men.

A study from the Department of Endocrinology at Boston Children's Hospital, an affiliate of Harvard Medical School, indicated that regular deep sleep in children is helpful in triggering the steady release of the hormones that cause puberty.