Have you ever heard a phrase like "The moon is full and you are invited to sleep"?
In fact, it is a medical theory that "the hormone that makes you sleepy 14 to 15 hours after being exposed to the sun is secreted and you become sleepy" instead of the moonlight.

The human brain has a pineal gland, from which a hormone called "melatonin" is secreted.
This will play a big role.

When we check the blood concentration, the concentration rises sharply from around 20-22 o'clock in the evening, and it regulates the internal clock in our body well. In other words, it plays a role in keeping the body active during the day and resting at night.

Let me introduce one related topic.

From comparative biology, other animals actually have pineal glands.
It is an important brain organ that secretes the sleep hormone melatonin.
In fish, the place exists as shown in the figure below, and in many animals such as chickens and fish, it functions as a so-called "third eye" that senses light.

In fact, the concept of the third eye is broad.
In various academic aspects, it is also called "inner eye, pineal eye" and is sometimes treated in mysticism and metaphysics.
In the area of ​​integrative medicine and yoga, the "chakra" in the middle of the forehead corresponds.
In manga and anime, Osamu Tezuka's science fiction manga "The Three-Eyed One" and Ultraseven's beam lamp are also models.

Doctor of Medicine Hiroshi Bando

* The fourth: Mechanism of sleep and awakening-Excerpt from the action of [pineal gland] and [melatonin]