Figure 1.

Fear conditioning with brain-stimulation CSs. a, Stimuli configuration. The CS was intermittent trains of brain stimulation (15 trains of 10 0.1 ms square pulses), which was paired with the footshock US during the conditioning phase. b, Changes in freezing during conditioning. During the preconditioning phase (B1–B3), none of the three groups showed any freezing to the CS. During the conditioning phase (C1–C6), significant increase in freezing was observed in all three groups. During the retention test (R1–R10), however, there was a significant group difference. Only the MGm-paired group showed significant freezing on retention compared with the preconditioning baseline. Freezing was essentially absent in the other two groups.