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Identifying interacting drives for sleep

Circadian and diurnal rhythms

Dr. Solet introduced her lecture with a picture of a lunar moth attracted to the light, explaining that the moth has evolved with diurnal rhythms (meaning day/night rhythms). She then displayed a picture of a store open 24 hours and used that as an example of how our changing lifestyle has wreaked havoc on our own diurnal rhythms. In the past, she explained how circadian rhythms were in sync with normal exposure; when it got dark outside, people would go to sleep.

Today, we live in a 24-hour society in which circadian rhythms can be undermined by artificial light and technology, which manifests as disrupted sleep patterns. Dr. Solet listed some of the culprits that we don’t even think about such as: electric lights on all the time, a culture of overwork, open 24/7 technology, insufficient exercise, a café on every corner where people can tank up to stay awake and can be tempted by treats that increase extra calories without realizing it, and the fact that people are limiting their sleep.

She raised the question “What are the drives that are being affected by our changing lifestyle, by this natural experiment we’ve undertaken, where we don’t have the normal exposure to light and balanced circadian rhythms?”

What regulates sleep/wakefulness

Wakefulness is regulated by two processes—Homeostatic and Circadian drives. The homeostatic drive for sleep and waking are neurobehavioral and physiological functions. The longer you are awake, the greater your homeostatic drive for sleep becomes.

The circadian drive, the night day light cycle, also drives sleep. Dr. Solet explained that when it is brighter, we are more alert. As an example, she used the case of someone staying up all night and perhaps at about 3 am getting really tired but then by 8 am getting a burst of energy, but by late afternoon the person wasn’t doing so well. It is just the overlap of circadian rhythms that causes that effect.

She presented a slide that had a graph of the circadian and homeostatic sleep timelines showing where they overlapped.

Individual differences/Chrono-types

In addition to the above processes, sleep is influenced by people’s inclination toward greater alertness in morning or evening; those two types are called Chrono-types. It is believed to be a biological proclivity that people are prone towards one or the other. People who stay up late are frequently called night owls, while those who get up very early are larks.