The role of the pineal gland in forming a conditioned reflex to time in rats.

The effects of pinealectomy and melatonin on time-associated conditioned reflex behavior were studied. Removal of the pineal gland hindered the formation of a conditioned reflex in conditions of a fixed time interval in rats. This was accompanied by a shortening of latency and excursions and an increase in the number of intersignal responses. Administration of melatonin (0.1 mg/kg) had the opposite effects, facilitating the development of the conditioned response to time and limiting motor activity.