Abstract
Infant rats rewarded for crawling by being allowed to suckle on the dry nipple of an anesthetized dam showed a decreasing rate of ultrasound production during acquisition and an increasing rate during extinction. These results suggest that infant rats can be stressed and are aroused as a result of successive nonrewards just as adult rats are. In addition, these results do not support the hypothesis that infant rats lack inhibitory mechanisms related to poorly developed neural centers.
