Relating to the pineal gland, a small endocrine gland in the brain that produces melatonin, the hormone that regulates sleep.
From Latin 'pinea' (pine cone) because the pineal gland resembles a tiny pine cone in shape. Renaissance anatomists named it based on this visual similarity.
The pineal gland is sometimes called the 'third eye' because it's sensitive to light and regulates circadian rhythms — some ancient cultures actually believed it was a spiritual organ, and modern science is only now discovering how deeply it affects our moods and sleep.
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