Memory for feeding time: Possible dependence on coupled circadian oscillators

Rats maintained on limited-access daily feeding schedules develop food-anticipatory activity rhythms which coexist with the photic circadian activity rhythm. These food anticipatory rhythms appear to depend upon a food-entrainable circadian oscillator which is separate and distinct from the light-entrainable circadian oscillator system. This study explored the long-term behavior of the putative food-entrainable oscillator in the presence and in the absence of a feeding schedule, and under light-dark cycles and constant light. The results suggest that a food-entrainable oscillator can show persisting self-sustained oscillations in the absence of a feeding schedule, and that the food- and light-entrainable circadian oscillators may show varying degrees of coupling, depending upon feeding conditions. Such a flexible coupling arrangement may allow the oscillator system to function as a "continuously consulted clock" in the adaptive temporal coordination of behavior with stable and unstable environmental periodicities.