Postprandial scanning by the rat (Rattus norvegicus): the importance of eating time and an application of "warm-up" movements

We observed the movements of rats (Rattus norvegicus) after they had eaten food pellets of various size or hardness. With rooted hindlegs, they made head scans, with vibrissae in contact with the substrate, that began over the area below where they had eaten and then expanded to include almost the entire area surrounding their body. Scanning was not contingent on the presence of dropped food. It occurred when rats ate on a screen through which any dropped crumbs could fall. It also occurred when rats were trained to find food at a location distant to where they ate. Although the duration of scanning increased in proportion to the size of food consumed, when eating time was varied, using food items of similar size but different hardness, scanning increased in proportion to eating time. Postprandial scans resemble the exploratory (warm-up) movements that bridge transitions from immobility to locomotion. We propose that a subset of the movements of warm-up are co-opted in this postprandial period. It is likely that in natural foraging situations they are useful for food searching. The results suggest that although the motor system may be conservative in the number of actions that it can produce, diversity is achieved by applying fundamental patterns to many uses.