Which brain region receives signals from ipRGCs to regulate circadian rhythms?

• A. Suprachiasmatic Nucleus
• B. Pineal gland
• C. Hippocampus
• D. Cerebellum

Answer: (A)

Signals detected by ipRGCs reach the brain’s master clock to set daily rhythms. These intrinsically photosensitive retinal ganglion cells respond to light and send information via the retinohypothalamic tract directly to the suprachiasmatic nucleus in the hypothalamus. The SCN acts as the central circadian clock, coordinating daily cycles in physiology and behavior. It also controls melatonin release by signaling the pineal gland indirectly through downstream pathways, aligning hormone production with the day-night cycle. The hippocampus and cerebellum aren’t primary regulators of circadian timing, and the pineal gland isn’t the direct recipient of ipRGC signals—melatonin is released there in response to SCN-driven cues. So the correct region is the suprachiasmatic nucleus.