The epithalamus is made up of the pineal gland, which processes melatonin and other enzymes sensitive to sunlight. It is often called the body's biological clock as the pineal gland helps dictate the body's sleep-wake cycle through the production of melatonin.
The epithalamus is located in the interior of the brain. It is a small area that is primarily covered by the pineal gland. This area of the brain is often described as the most mysterious part because it was the last gland identified within the endocrine system. It was once referred to as a person's "third eye," and it was thought to serve as the place where the soul exists in the body, as well as the primary place where thoughts were developed in the brain. This was mostly because of its strong relation to processing light.