Disturbances of the circadian rhythm and insomnia
The Circadian Rhythm is a 24 hour biological rhythm that persists in the absence of external cues but can be adjusted or reset to match a local time. It can also maintain itself in the presence of changes in temperature (this is important for biological organisms that experience shifts in temperature).
In humans the circadian rhythm is regulated by the hypothalamus region of the brain. The hypothalamus is positioned close to the optic nerve, which relays light signals from the eyes to the brain. This is important because the brain regulates the circadian rhythm mainly by its sensation of light. The main action of this regulation involves the release of the hormone melatonin when the brain perceives darkness. Melatonin causes sleepiness. When the brain perceives light it shuts off the release of melatonin, and this wakes you up.
Under normal conditions a person’s circadian rhythm keeps them dynamically in sync with a 24 hour cycle of wakefulness and sleep that corresponds to the day-night cycle. However, this rhythm can be broken by activities, e.g., shift work and jet lag, or lifestyle habits, e.g., staying up late or sleeping late.
Being out of sync with the normal circadian rhythm has two classifications, known as:
- Advanced sleep phase syndrome
- When a person has the urge to fall asleep earlier than normal, best illustrated by the experience of jet lag incurred when flying from east to west.
- Delayed sleep phase syndrome
- When a person has the urge to fall asleep later than normal, best illustrated by the experience of jet lag incurred when flying from west to east.
There are two main treatments for circadian rhythm disorders. These are:
- Phototherapy
- Phototherapy involves using light to trigger wakefulness at a desired time of day (or night). This can mean using artificial or natural light at the time of day (or night) when a person desires to be awake but currently feels sleepy
- Behavioral therapy
- Behavioral therapy involves using chronotherapy, wherein a person with delayed sleep phase disorder (sleeping too late) pushes the hour at which they go to bed forward by one or two hours every other day until they are in sync with a normal bedtime cycle