LONG-TERM-MEMORY AND EXTINCTION OF RABBIT NICTITATING-MEMBRANE TRACE CONDITIONING

Long-term memory for and extinction of trace conditioning were examine d using the rabbit nictitating membrane response (NMR) preparation. Ra bbits were trained on four consecutive days with 80 trials of a 100-ms tone followed 500 ms later by a 100-ms periorbital electrical pulse. After a period of 1, 2, 3, or 6 months in their home cages, rabbits we re given four consecutive days of 80 tone-alone extinction trials foll owed by a single day of 80 reacquisition trials. The results showed th e following: (1) rabbit NMR conditioned responses following trace cond itioning were reduced to approximately 55% of acquisition levels after an interval as short as a month between acquisition and extinction. A ll but one rabbit responded at baseline levels (<2%, CRs) 6 months fol lowing trace conditioning. In other words, there was a significant amo unt of forgetting of the association acquired during trace conditionin g. (2) Conditioned responses that occurred 1, 2, or 3 months following acquisition were extinguished whereas responses that were absent foll owing an interval of 6 months tended to reemerge over the course of ex tinction trials. (3) Reacquisition of the classically conditioned NMR in rabbits that had returned to baseline after extinction was signific antly faster than initial acquisition levels in all groups and suggest ed a substantial level of savings. (C) 1998 Academic Press.