Prior exposure to inescapable electric shock in rats affects extinction behavior after the successful acquisition of an escape response

In Expt 1, rats exposed to 64 inescapable electric shocks in a restrainer or merely restrained were later given either 0, 5, 15 or 30 escape/avoidance training trials with a two-way shuttlebox procedure that does not lead to interference with escape acquisition due to prior exposure to inescapable shock. After escape training all rats were given an escape/avoidance extinction procedure in which shock was inescapable. The rats which had received prior exposure to inescapable shock responded less often and with longer latencies in extinction than did the restrained rats. Experiment 2 demonstrated that this effect is caused by the inescapability of the initial shock treatment. These results were explained in terms of (a) associative interference which minimized the effect of shuttlebox escape training for the preshocked subjects, and (b) a stronger tendency to recognize the presence of an inescapable shock situation during extinction for the preshocked subjects. The relationship between these results and previous work demonstrating that exposure to the escape contingency mitigates the effects of inescapable shock exposure was also discussed.