Figure 3.

Under low footshock conditions, PL microstimulation increases fear expression, whereas IL microstimulation decreases fear expression. (A) On Day 2, PL microstimulation (n = 8) increased conditioned freezing whereas IL microstimulation (n = 6) decreased freezing, compared with the Unstim group (n = 12). On Day 3, there was no significant difference between groups (ANOVA, P = 0.08). (B, left) Bar graph showing percent freezing for the very first extinction trial on Day 2 (one-way ANOVA P < 0.001; Unstim vs. IL: P = 0.020; Unstim vs. PL: P = 0.036; IL vs. PL: P < 0.001). (Right) Microstimulation delivered in the absence of conditioned tone had no effect. CS = conditioned stimulus (tone).