Activity in anticipation and in succession of a daily meal.

When exposed, in otherwise constant conditions, to a schedule with one single meal per day, rodents anticipate the time of food availability by an increase in locomotor activity while the main circadian rhythm continues to free-run with a period different from 24 h. The anticipatory activity (AA) is considered a component which is uncoupled from the light-entrainable circadian system and controlled by a food-entrainable oscillator. In this report it is shown that, in addition to AA, sometimes a burst or band of activity appears which succeeds the feeding time (SA). AA and SA seem to belong to one another, both being controlled by the same food-entrainable oscillator. The band of activity constituted by the combination of both AA and SA, though temporarily suppressed during and immediately after the meal, follows, as a whole, the rules of entrainment as known from circadian systems.