What part of the brain is involved in seasonal affective disorder?

The suprachiasmatic nucleus (SCN) plays a crucial role in regulating circadian rhythms, which are the physical, mental, and behavioral changes that follow a daily cycle. This nucleus, located in the hypothalamus, is particularly sensitive to light and helps synchronize the body’s internal clock with the external environment. In seasonal affective disorder (SAD), changes in light exposure, particularly during shorter days in the winter months, can lead to disruptions in this circadian timing system.

The SCN influences the secretion of melatonin by the pineal gland; melatonin production typically increases in darkness and decreases in light. In individuals with SAD, the altered photoperiod can affect melatonin levels, leading to mood disturbances and depressive symptoms that are characteristic of this disorder. By regulating melatonin and circadian rhythms, the SCN is fundamentally linked to how changes in light exposure affect mood and behavior, which is a central aspect of seasonal affective disorder.