This is all thanks to a substance called melatonin, which is produced by a type of pineal gland in the brain.

This is the same kind of tissue that produces serotonin, which is the ‘happy hormone’. These chemicals were discovered in the 1950s by the Swiss biologist Arvid Carlsson. The first ‘happiness hormone’ (5-HTP) was later discovered in the 1990s by the UK academic James Robinson. To make melatonin, the pineal gland releases serotonin into the bloodstream (serotonin is also produced by other sources, like the pancreas). This helps regulate the body clocks of the day and the night.

This explains why there are always a few hours between sleep and wake: it’s because the cells of the body, and more specifically the pineal gland, require serotonin to stay synchronized with the environment that surrounds them on the 24-hour cycle. Studies on the role of melatonin in the body’s wake/sleep cycle are now being expanded into neuroscience. A 2021 study showed that rodents exposed to melatonin had an improved learning performance and an improved cognitive processing. The study was conducted on the effects of melatonin in rats exposed to repeated stress. In another study, researchers from University College London revealed that chronic melatonin administration reduced depressive behaviors in mice exposed to chronic stress.

They also found that the hippocampus, an important brain area involved in learning and memory, is essential for this effect. In a study in 2015, the U.S. researchers published in the journal Cell Prolife found that melatonin helps prevent blood platelet aggregation during chronic stress. They also found that melatonin is essential for the production of neurotrophic factors, which help in the repair of nerve cells. These findings were in response to a study published in the journal Nature Medicine in 2016, which reported that the body’s production of melatonin is essential for the maintenance of brain health and fitness.

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Researchers continue to experiment with the use of melatonin and serotonin. In a 2014 study, the German biologist Andreas Kahl reported that rats exposed to chronic stress had lower levels of serotonin in the hippocampus. This lower secretion of the ‘happy hormone’ can affect the sleep-wake rhythms, which can cause the rats to sleep less and wake up later. It’s in this scenario that Kahl’s team investigated melatonin as a replacement for serotonin. In 2016, researchers from the University of Gothenburg conducted a study on the role of melatonin. They revealed that the administration of the hormone to mice exposed to stress reduced depressive behavior.