Which part of the brain is identified as the central clock that regulates melatonin?

The suprachiasmic nucleus (SCN) is identified as the central clock of the brain that regulates melatonin. This small group of cells, located in the hypothalamus, plays a crucial role in circadian rhythms, which are the body's natural 24-hour cycles. The SCN receives direct input from the retina through the retinal ganglion cells, allowing it to synchronize with light and dark cycles in the environment.

As night approaches and light becomes scarce, the SCN signals the pineal gland to produce and release melatonin, a hormone that helps regulate sleep-wake cycles. Melatonin production thus peaks during the night, promoting sleep, and diminishes as morning approaches, facilitating wakefulness. This entire process highlights the pivotal function of the SCN in controlling not only melatonin levels but also overall circadian rhythm.

The other parts of the brain mentioned do not have the same regulatory role over melatonin. Retinal ganglion cells are involved in transmitting visual information to the SCN but do not produce melatonin themselves. The hippocampus is primarily associated with memory and learning, while the thalamus acts as a relay station for sensory information but lacks direct involvement in the regulation of melatonin and circadian rhythms.