Circadian properties of food anticipatory activity re-examined: entrainment limits and scalar timing in operant and general activity

Rats display anticipatory activity (FAA) to daily feeding opportunities. Early chronobiological research indicated that feeding schedules deviating from 24-hours failed to elicit FAA, suggesting that a circadian oscillator mediates this behavior. More recent work using operant measures of anticipation, uncommon to chronobiology, has reported that rats can anticipate non-circadian intervals and that this anticipation shows hallmarks of interval timing rather than oscillator control. To test whether operant and non-operant behaviors may be controlled by different timing mechanisms, we re-examined formal properties of FAA using lever pressing and motion sensors. Rats maintained in a 12:12 light-dark cycle or in constant light failed to show anticipation to meals at 18h intervals, but robustly anticipated meals at 24h intervals. FAA failed to scale with intervals between light changes and mealtime, violating the hallmark property of interval timing. These results support a food-entrained oscillator model of FAA and fail to provide evidence that cue-dependent interval timing contributes to FAA.