A developmental comparison of trace and delay eyeblink conditioning in rats using matching interstimulus intervals

The effects of conditioning paradigm and interstimulus interval (ISI) were evaluated in this study of the development of associative learning in rats. The acquisition of classical eyeblink conditioning (EBC) was examined in two paradigms (trace vs. delay), with three different ISIs (short, medium, or long) at two ages (postnatal Days 21-23 or 29-31). These data provide the first parametric analysis of ISI in developing animals trained with trace EBC procedures. Further, by comparing trace and delay EBC, it was determined that when ISI is held constant, acquisition is similar for both conditioning paradigms regardless of developmental age. This suggests a similar ontogeny of associative processes for delay and trace EBC that relies on common neural substrates. However, conditioned response timing (onset and peak latencies) was affected by age and paradigm, suggesting that different neural mechanisms may play a role in timing delay versus trace conditioned responses.