The ontogeny of classical conditioning in the neonatal rat with varied CS-UCS intervals

Abstract

Leg flexion to shock after vibration was studied in neonatal rats during the first, third, sixth and twelfth days of age, using CS-UCS intervals of 300, 600 and 1200 msec. Every tenth trial was a test trial (no UCS) for a block of 80 trials per S, and responses to CS that anticipated the UCS were measured during the other nine trials of a block. There was little hard evidence of learning during the early days of life, but conditionability steadily increased as a function of age. While on the first day of age the 1200 msec interval produced more test trial CRs than the 600 msec interval, this phenomenon was reversed on the twelfth day of age.