The pineal gland is also called the supracerebral gland. Located below the posterior tail of the corpus callosum, it looks like a pine cone and is about 1 cm long. At an early age, the pineal gland developed, and then gradually degenerated. Generally, it began to calcify and shrink at the age of 7 ~10. Melanin, a hormone secreted by it, has the function of inhibiting gonadal development, especially in childhood, and has the function of stopping sexual maturity.

The synthesis and secretion of melatonin are regulated by light and darkness. Continuous light can inhibit the secretion of pineal gland, while darkness can stimulate the secretion of pineal gland. Therefore, its secretion changes periodically day and night. At noon 12, the secretion is the lowest; At midnight, the secretion is the highest. This periodicity is obviously related to human menstrual cycle. In addition, the pineal gland may send a "time signal" to the central nervous system through the secretion cycle of melatonin, thus affecting the body's time biological effects, such as sleep and awakening. However, whether the pineal gland is the "biological clock" that affects or regulates the circadian rhythm of animals remains to be further proved. It is also reported that melatonin can strengthen the central inhibition process, thus promoting sleep. Therefore, it has been used to treat epilepsy epilepsy epilepsy.