Light input is carried along the retinohypothalamic tract (RHT) to the SCN.

• A. False
• B. True
• C. It goes to the Brainstem
• D. It goes to the Cerebellum

Answer: (B)

Light input sets circadian rhythms through a direct retinal pathway to the brain’s master clock. Special retinal cells that are intrinsically photosensitive detect ambient light and send signals via the retinohypothalamic tract straight to the suprachiasmatic nucleus in the hypothalamus. When this input arrives, the SCN adjusts its activity and synchronizes the body's daily rhythms to the day-night cycle. This pathway is specifically for circadian entrainment, not for routing light information to other brain regions like the brainstem or cerebellum, which are involved in different functions. So the statement is true.