The Science of a Good Night’s Sleep By Margaret Blattner, MD, PhD
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hile sleep seems “quiet and restful”, it is in reality an active process and involves complex neurophysiology, engaging a number of brain systems. This multi-component physiology leads to restful sleep night after night but also presents multiple vulnerabilities that can lead to sleep disruption and excessive daytime sleepiness. Healthy sleep is important for physical and mental health. Even one night of disrupted sleep can impact mood, memory, and performance the next day. In addition, chronic disruptions in sleep impact health and wellness longterm. Often sleep scientists think about the regulation of sleep and wake as two connected processes: the sleep homeostatic drive (often referred to as Process S) and the circadian rhythm (Process C). Process S is based on the principle that the longer a person is awake, the sleepier they become (and, conversely, the longer one has been sleeping, the lower the sleep drive). Sleep
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drive is highest at the end of the day and is increased by sleep deprivation (due to things like study, work, taking care of children overnight, or illness). Sleep drive can also be diminished by taking a mid-day nap. Process S also decreases throughout the night while sleeping. It tends to be lowest in the morning; people usually find it easier to fall back to sleep after waking up early in the night rather than late in the night. This sleep homeostatic drive is impacted by even mild sleep deprivation. For example, getting 7 hours of sleep when a person feels best with 8 hours of sleep can cause sleepiness to intrude during the day or at unwanted times. Achieving healthy sleep is difficult when this process is impacted by pathological sleep deprivation, such as chronic insomnia and chronic sleep insufficiency due to school, work, or family responsibilities. Process S does not switch off immediately on waking up, causing a sluggishness called “sleep inertia” which usually lasts 15-30 minutes.
