What is the master circadian clock in the brain called?

The master circadian clock in the brain is known as the suprachiasmatic nucleus (SCN). This small region of the hypothalamus is critically involved in regulating the body's circadian rhythms, which are the physical, mental, and behavioral changes that follow a daily cycle, responding primarily to light and darkness in the environment.

The SCN processes information about light received from the eyes and adjusts the body’s internal clock accordingly, influencing various physiological processes such as sleep-wake cycles, hormone release, and body temperature. This synchronization with the environmental light-dark cycle is essential for maintaining proper functioning within the body's biological systems.

The other structures listed play different roles in brain functions but do not serve as the master clock. For example, the ventrolateral preoptic nucleus is involved in promoting sleep, the thalamus acts primarily as a relay station for sensory information, and the substantia nigra is associated with reward and movement control, particularly in relation to Parkinson's disease. These functions, while important, do not involve direct regulation of circadian rhythms like the SCN does.