An ANOVA of SCR during the extinction memory recall test (first two CS+E vs. first two CS+U trials) revealed a significant drug by stimulus interaction [F(1,27) = 4.80, p < 0.05]. The THC group exhibited smaller SCRs to the stimulus that had been previously extinguished during the previous extinction learning phase compared with the stimulus that had not been extinguished [0.22 ± 0.08 for CS+E vs. 0.35 ± 0.09 for CS+U], whereas the PBO group did not [0.37 ± 0.11 for the CS+E vs. 0.23 ± 0.09 for the CS+U]. Moreover there was a significant difference in the mean differential SCR to the CS+E minus the CS+U between the THC and PBO groups during the extinction memory recall test [Figure 3; t(27) = −2.29, p < 0.05]. Consistent with these findings the PBO group displayed spontaneous recovery of conditioned fear responses to the CS+E during extinction recall, as evidenced by significantly greater SCRs to the CS+E during extinction recall than during late extinction learning [Late Extinction learning: 0.13 ± 0.04 vs. Extinction Recall Test: 0.37 ± 0.11; t(14) = −2.45,
