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Thanellou, Alexandra

Psychology

2007

MA

Reinstatement, the return of an extinguished response when animals are exposed to the unconditioned stimulus (US) alone following extinction, was investigated in eyeblink classical conditioning. In experiment 1, animals of the experimental group (n=9) were exposed to US alone presentations 24 hours after extinction and were tested 24 hrs later for the return of responding to the CS. The control group (n=9) stayed in the apparatus without receiving any US presentations. Results showed that there were no significant differences in the percentage of conditioned responses (CRs) between the two groups during testing. In experiment 2, animals of the experimental group (n=9) were exposed to US alone presentations 24 hours after extinction and were tested 5 min later for the return of responding to the CS. The control group (n=8) stayed in the apparatus without receiving any US presentations.
Results, again, showed that there were no significant differences in the percentage of CRs between the two groups during testing. In experiment 3, a long, discrete cue served as a context within which each CS-US trial occurred in an attempt to maximize context processing, which, in other preparations, has been shown to be required for the reinstatement of extinguished conditioned performance. The reinstatement group (n=6) was exposed to US-alone trials in the presence of the long cue (a houselight) whereas the control group (n=4) stayed in the apparatus without receiving any US presentations and just received the long cue. Results showed no differences in the percentage of CRs between the two groups. Although reinstatement can be obtained in other types of conditioned behaviors, the present experiments provided no evidence that the extinguished eyeblink response can be reinstated.