Ontogeny of delay versus trace eyeblink conditioning in the rat

The ontogeny of delay versus trace eyeblink conditioning was examined in 19 -, 23-, and 30-day-old rat pups. Pairings of a tone conditioned stimulus (C S) and periocular shock unconditioned stimulus (US; 100-ms) were presented in one of three conditioning paradigms: standard delay [380-ms CS, 280-ms i nterstimulus interval (ISI)], trace (380-ms CS, 500-ms trace interval), or long-delay (980-ms CS, 880-ms ISI). The results of two experiments indicate d that standard delay conditioning emerged between 19 and 23 days of age wh ereas trace and long-delay eyeblink conditioning emerged more slowly from p ostnatal Days 19 to 30. Because the acquisition profile for long-delay para lleled that of trace and not standard delay, it appears that the relative d eficits in the emergence of trace eyeblink conditioning during development reflect difficulty in forming associations over long ISIs rather than the s hort-term memory demands of the trace conditioning paradigm. (C) 2000 John Wiley & Sons, Inc.