[Operant conditioning with thermal reinforcement in the newborn rat]

In previous experiments, we studied the acquisition of instrumental locomotor responses reinforced by thermal stimuli, in one to ten-day-old rats. In these tasks, there was a precise topographic relation between the behavior to be conditioned and the reinforcement. In the experiment reported in the present paper, one to eight-day-old rats were tested in an operant conditioning task, where the operant (OP) was a non locomotor behavior, the raising of the head. At each day of age, two paired groups were compared: a "contingent" (C) and a "non contingent" (NC) group. Each OP (satisfying an amplitude criterion) of a C rat was reinforced by the application of a 30-35 degrees C air-stream during ten seconds. The NC rat of the same pair received the same number of air-streams during the session, but these stimuli were unrelated to its behavior. The duration of the session was ten minutes. Mean frequency of OP was higher in C than in NC groups, at one, two, six, seven and eight day of age. Absence of significant differences between C and NC groups at three, four and five days of age could be due to the competition between OP and the emerging locomotor behavior.