Rats anticipate and discriminate between two daily feeding times

Intact rats and rats bearing lesions of the suprachiasmatic nuclei (SCNX rats) were trained to obtain food by pressing either of two levers located on opposite sides of a cylindrical cage. Intact rats were maintained in constant light (LL) and under daily light-dark (LD) cycles, SCNX rats in LL only. A restricted daily feeding schedule was next imposed, such that pressing one lever provided food for a limited duration (1 or 2 hr) at one time of day while pressing the second lever provided food for the same duration at another time of day. Most rats generally showed anticipatory lever-pressing preceding both daily feeding times, and several discriminated between the two, pressing the lever appropriate for each feeding time more than the inappropriate lever. Discrimination performance was better in intact rats in LD than in intact or SCNX rats in LL. These results indicate that rats can associate different food locations with different times of day, an ability previously known only in honeybees and birds.