What is a 'Z-Score'. A Z-score is a numerical measurement of a value's relationship to the mean in a group of values. If a Z-score is 0, it represents the score is identical to the mean score. Z-scores may also be positive or negative, with a positive value indicating the score is above the mean and a negative score indicating it is below the mean.
The pineal gland, also known as the pineal body, is an important endocrine gland that produces the hormone melatonin. Melatonin plays a key role in the sleep/wake cycle and the bodyâs response to sunlight. The pineal gland is a small, pinecone-shaped mass of glandular tissue about 1/3 of an inch (8 mm) long.
Melatonin â A signal of darkness and marker for circadian rhythms Melatonin is a naturally occurring hormone that is key to sleep and the sleep-wake cycle in humans and animals 8. In the body, melatonin is produced by the pineal gland in the brain when night falls. The retina detects failing light, and the level of melatonin gradually increases, reaching its peak in the middle of the night in natural circumstances 9.