Odor from rats tasting a signal of illness.

Rats running in a runway emit discriminable odors when encountering reward (R) or nonreward (N) goal events, and subsequent rats use these odors as discriminative stimuli to alter their approach speeds. In the present studies, a third goal event, aversively conditioned denatonium saccharide (A), was introduced. In Experiment 1, rats evidently emitted an odor when encountering the A goal event, because in the presence of this A odor subsequent conspecifics slowed their approach to the goal, much like their behavior on N trials. In Experiment 2, when N odor signaled R goal events and A odor signaled A goal events, rats approached quickly to N but slowly to A, indicating that they could discriminate N and A odors at the given concentrations. These studies indicate that rats emit an odor when confronted with a signal of impending illness and that this odor seems readily discriminable from R and N odors.