Computational and entrainment models of circadian food-anticipatory activity: evidence from non-24-hr feeding schedules.

Rats anticipate a daily meal, provided that meal onset intervals are within a circadian (22-31 hr) range. Food-anticipatory activity (FAA) has been interpreted as evidence for a food-entrained circadian pacemaker or for a computational process that uses stored representations of pacemaker phase. The models make different predictions concerning the symmetry and history dependence of the circadian limits to FAA. To test those predictions, rats were entrained to 24-hr light-dark and feeding cycles and then exposed to feeding cycles of 21, 22, 25, 26, or 27 hr. Rats showed strong FAA to feeding cycles > or = 24 hr, but not to schedules < 24 hr. Prior exposure to long cycles did not promote anticipation under short cycles. Meal omission tests confirmed that failure to observe FAA to < 24-hr feeding cycles was not a result of masking by early mealtimes. These and other aspects of the results are consistent with the entrained oscillator model of FAA.