What is the role of the suprachiasmatic nucleus (SCN) in the brain?

The suprachiasmatic nucleus (SCN) plays a crucial role in regulating the sleep-wake cycle, acting as the body's primary circadian pacemaker. This small cluster of neurons, located in the hypothalamus, receives direct input from the retina, which allows it to sense light and dark cycles. By responding to this photic input, the SCN helps synchronize the body's internal biological clock with the external environment, influencing various physiological processes that follow a daily rhythm.

One of its key functions is to control the release of melatonin, a hormone produced by the pineal gland that promotes sleep. During the night, when darkness signals the SCN, melatonin production is increased, leading to feelings of sleepiness. Conversely, during the day, light inhibits melatonin secretion, helping to maintain wakefulness. This regulation of the sleep-wake cycle by the SCN is essential for maintaining overall health, mood stability, and cognitive function.