Ontogeny of conditioned inhibition of conditioned respiratory suppression in kittens

Excitatory and inhibitory classical conditioning were examined in 4-week-old, 8-week-old, and 12-week-old kittens. Conditioned respiratory suppression (CRS) was a measure of conditioned fear. The inhibitory conditioning procedure was designed to model the schedule of events that normally accompanies successful coping behavior: The safety signal predicted the cancellation of shock that would otherwise follow the danger signal, rather than simply the absence of shock. Before training, the stimuli elicited small unconditioned respiratory suppression in the 4-week-old and 8-week-old kittens, but not in the juvenile, 12-week-old kittens. During training, danger signals came to elicit robust CRS after 3-4 sessions (20-30 trials) in every age group. Acquisition of inhibition of CRS was also observed within 2-3 days (20-30 trials). The effectiveness of inhibitory stimuli improved significantly with age. The safety signal also inhibited fear (CRS) elicited by a second danger signal. Thus, the kittens learned inhibition to the safety signal per se, rather than having learned to discriminate some nonreinforced configured cue from the danger signal presented alone.