Fig. 3.

Massed or distributed extinction trials immediately after fear conditioning. Rats received 45 or 225 extinction trials 15 min after fear conditioning. For two groups of rats (EXT45–12 and EXT225–12), the extinction trials were massed (12-sec ISI). The EXT45–60 group was treated identically to that in Experiment 1 (45 trials; 60-sec ISI). Total time in the extinction context was equated in all of the groups. The graph displays freezing behavior during the retention test 24 h after extinction. Data were normalized as in Fig. 1D. All data are means ± SEM.