Figure 2.

ChR2 activation of IL neurons facilitates subsequent retrieval of extinction. A, Left, Micrograph showing the expression of ChR2 within IL. Middle, Green areas represent the minimum (darker) and the maximum (lighter) areas of ChR2 expression in IL. Right, Black dots represent the location of optic fiber tips within IL. B, ChR2 activation of IL (at 20 Hz) during extinction training reduced expression of freezing and facilitated extinction retrieval the following day, compared with eYFP controls (n = 10 per group). C, ChR2 activation of IL neurons in the first trial block of extinction retrieval (Day 3) facilitated retrieval (p = 0.04). D₁, ChR2 activation of IL did not alter locomotion in an open-field task (n = 6 per group, 3 min laser off vs on). D₂, ChR2 activation of IL reduced the rate of spontaneous bar pressing for food (n = 6–7 per group; 5 min laser off vs 5 min laser on, 2 trials). Data are shown as mean ± SEM in blocks of two trials; *p < 0.05. Blue bar, laser illumination. PL, prelimbic cortex; IL, infralimbic cortex; cc, corpus callosum; Cond, conditioning; x, baseline (pretone) freezing levels.