Although it has been more than 80 years since Pavlov first observed spontaneous recovery from extinction, the mechanisms underlying this phenomenon remain a mystery. The majority of the proposed models attribute spontaneous recovery to a time-induced change in extinction-related processes. Recent findings, however, point also to the importance of elapsed time since acquisition, not just since extinction. These findings suggest that various temporal parameters of the learning episode may be explicitly represented in order to guide future choice on whether an animal should invest to a signal that has produced more than it has failed. In the present experiments, we used a conditioned magazine approach in the mouse to investigate whether and how various temporal parameters of acquisition affected spontaneous recovery. We found that prolonging the duration of acquisition, either by distributing the same number of acquisition trials across more sessions, or by spacing the same conditioning sessions more widely, augmented spontaneous recovery. Further investigation of the former effect revealed that the session is an important unit of learning experience, while the number of trials within a session is not a primary determinant for spontaneous recovery. Finally, we quantitatively characterized extinction at the level of the individual subject and found it to be abrupt. It took a few trials to appear but became complete almost immediately.Ph.D.Includes bibliographical references (p. 82-87)
