Signaled and unsignaled footshock modulates mPFC single-unit activity.

<p><b>(A)</b> Day 1 experimental design; histological placement of the center of each electrode array in mPFC is shown. Each array targeted both PL (8 wires) and IL (8 wires) in the right hemisphere. Coronal sections represent (left to right) coordinates +3.2 and +2.8 relative to bregma in the anteroposterior plane. <b>(B)</b> Signaled (red) and unsignaled rats (blue) displayed no significant difference in freezing behavior during the post-shock 15 min stimulus-free period. The spontaneous firing rate of all neurons was normalized to the pre-conditioning baseline for each brain region and shock group. Normalized firing rate for PL and IL for signaled and unsignaled, (time 0 is immediately after the last shock). <b>(C)</b> Heat maps showing shock-induced changes in firing rate for individual neurons split by group and brain region. Data during the shock trials were not recorded. All values are means ± SEM.</p

Differential firing in PL versus IL predicts freezing behavior.

<p><b>(A</b>) Freezing (circles) was similar across Days 1 (3 min post-shock period) and 2 (tones 4 and 5) in signaled rats, whereas it decreased markedly on Day 2 in unsignaled animals. Relative neural activity (PL minus IL) was similar in magnitude (and positive) across days for the same time periods in signaled rats, but also decreased in magnitude markedly on Day 2 in unsignaled animals. <b>(B)</b> Linear regression analysis showing the PL vs IL difference during tones 4 and 5 plotted against freezing levels for the same time period. This analysis revealed a strongly positive correlation between the two variables when including rats from both shock groups. All values are means ± SEM. *<i>p</i> < 0.01.</p

Fear recall suppresses mPFC population level single-unit activity.

<p><b>(A)</b> Day 2 design. <b>(B)</b> Upon tone presentation on Day 2, signaled (red) and unsignaled rats (blue) displayed opposing freezing patterns. (<b>C, D</b>) Average normalized firing rate data from PL and IL are binned in 5 sec increments for the duration of the session. Gray dashed lines indicate tone onset (tone response is the bar immediately to the right of dashed line) for the 5 tones. Signaled rats exhibited robust tone-evoked responses that are superimposed on the overall suppression of neural activity in both PL and IL, as compared to the general increase in firing in unsignaled PL and IL. <b>(E)</b> Heat maps plotting tone-evoked responses for neurons from signaled and unsignaled rats. <b>(F)</b> Normalized tone-evoked histogram averages plotted in 100 msec bins for PL and IL. Previously signaled rats showed robust tone-evoked responses in both PL and IL around tone onset (first 200 msec) compared to unsignaled rats. No difference was observed between brain regions when comparing within a shock group. All values are means ± SEM.</p