Long-interval timing is based on a self-sustaining endogenous oscillator

The mechanism of anticipating long-intervals (16–21 h) was investigated. Rats earned food by interrupting a photobeam in a food trough during 3- or 4-h meals. Intermeal intervals were 16, 21, and 24 h (offset to offset) for independent groups of rats (n = 8 per group). After approximately a month of experience with the intermeal intervals, the meals were discontinued. The rate of visiting the food trough increased as a function of time before the meal. When meals were discontinued, visits continued to be periodic. The periodicity was approximately 21 h after 16- and 21-h intermeal intervals and approximately 28 h after 24-h intermeal intervals. These data suggest that long-interval timing is based on a self-sustaining, endogenous oscillator.