Circadian effects of timed meals (and other rewards).

Mammals organize many of their activities around rhythmic events in their environments. Primary among these events is the daily light-dark cycle. However, for many animals, food availability is rhythmic or quasi-rhythmic and is therefore a potential synchronizing cue. While circadian rhythms in both behavior and physiological activity can be entrained in animals via meal-feeding schedules, the mechanism by which this occurs remains poorly understood. Similarities between the circadian effects of restricted feeding and the effects of chronic methamphetamine treatment may be indicative of a common mechanism. This article argues that reward (or the arousal that accompanies it) may be the final common pathway for such nonphotic circadian inputs.