Scientists sleep like the rest of us—though Thomas Edison was reported to only do it two hours a day—but how it works is still not well-understood. New discoveries, however, are helping bring us to a more complete understanding of what sleep is. For example, researchers at the RIKEN Brain Science Institute in Japan recently found that a brain region called the lateral habenula plays an important role in the lightest stage of sleep, the rapid eye movement or REM phase, when the best-recalled dreams happen.
When you’re awake, the lateral habenula is one of the parts of the brain that deals with stress and pain, and reacts to unpleasant events. It is heavily involved in processing the neurotransmitter serotonin, which has a number of roles in the brain. Serotonin is associated with happiness and is one of the brain’s “reward chemicals,” part of a feedback system that makes things that are good for the body feel good. For example, eating healthy food—food with a nutrient ratio historically well-suited to the body’s needs—releases serotonin. Serotonin also helps start the sleep cycle and shortens REM sleep periods.
The researchers found that the lateral habenula, by metabolizing serotonin, lowers the levels of the neurotransmitter in the blood; they hypothesized that this may explain part of the connection between depression and insomnia. In many cases, clinical depression is associated with low levels of serotonin. That means the same neurochemical deficit that contributes to depression also makes it harder to fall asleep, and makes the sleep patients do get shallower and less restful.
This connection is stronger since insomnia itself can exacerbate depression; it causes anxiety, also associated with low serotonin, and like depression reduces pleasure in otherwise enjoyable activities. Drugs that increase serotonin levels, such as selective serotonin reuptake inhibitors, which slow the process by which serotonin released in the brain is expended, are used for depression, anxiety, and insomnia. Similarly, a carb-heavy diet increases the body’s production of serotonin, as does exercise, and these things are known to help both sleep and depression.