The ontogeny of learned inhibition.

Previous studies have examined the maturation of learning and memory abilities during early stages of development. By comparison, much less is known about the ontogeny of learning and memory during later stages of development, including adolescence. In Experiment 1, we tested the ability of adolescent and adult rats to learn a Pavlovian negative occasion setting task. This procedure involves learning to inhibit a behavioral response when signaled by a cue in the environment. During reinforced trials, a target stimulus (a tone) was presented and immediately followed by a food reward. On nonreinforced trials, a feature stimulus (a light) was presented 5 sec prior to the tone and indicated the absence of reward following presentation of the tone. Both adult and adolescent rats learned to discriminate between two different trial types and withhold responding when the light preceded the tone. However, adolescent rats required more sessions than adults to discriminate between reinforced and nonreinforced trials. The results of Experiment 2 revealed that adolescents could learn the task rules but were specifically impaired in expressing that learning in the form of withholding behavior on nonreinforced trials. In Experiment 3, we found that adolescents were also impaired in learning a different version of the task in which the light and tone were presented simultaneously during the nonreinforced trials. These findings add to existing literature by indicating that impairments in inhibitory behavior during adolescence do not reflect an inability to learn to inhibit a response, but instead reflect a specific deficit in expressing that learning.