Location: Near the center of the brain, between the two hemispheres

Function: Scientists are still trying to figure out exactly how the pineal gland works and what role it plays. Named for its pine cone shape, the gland produces the hormone melatonin, which controls our internal clock and our sleeping patterns. It’s sensitive to light, pumping out more melatonin when it’s dark and less when it’s light.

Some suggest this process might also be behind seasonal affective disorders, which affect people particularly in northern climates where the days are shorter in winter time.

In ancient times, the pineal gland was considered the “third eye” and thought to have magical powers. The philosopher Descartes suggested it was the resting place of the soul. In birds, the pineal gland contains magnetic materials that help with navigation. Some researchers suspect the gland also helps humans with their innate sense of direction.

Potential problems: Pineal gland tumors and pineal region tumors are fairly rare, accounting for less than 1.5 percent of all human brain tumors. There’s some suggestion that certain sleep and mood disorders might stem from problems with the pineal gland as well.

— Markian Hawryluk

Sources: The Hormone Society, Colorado State University, BBC Health.