Timing of behavioral responding to long-duration Pavlovian fear conditioned cues

Abstract

Behavioral responding is most beneficial when it reflects event timing. Compared to reward, there are fewer studies on timing of defensive responding. We gave female and male rats Pavlovian fear conditioning over a baseline of reward seeking. Two 100-s cues predicted foot shock at different time points. Rats acquired timing of behavioral responding to both cues. Suppression of reward seeking was minimal at cue onset and maximal before shock delivery. Rats also came to minimize suppres-sion of reward seeking following cue offset. The results reveal timing as a mechanism to focus defen-sive responding to shock-imminent, cue periods.

Figure 1.. Experimental design and baseline nose poke rates.

(A) Rats received 100-s cue presentations over a baseline of rewarded nose poking. Shock was delivered at the offset of the shock100 cue, while shock was delivered 50 s into the shock50 cue. Yellow vertical line and shock icon indicate time shock was delivered. (B) Mean ± SEM suppression ratio is shown for fe-male (black) and male (grey) rats over the 20 Pavlovian fear conditioning sessions. Blocks are identified below the x-axis: 1 (magenta), 2, (brown), 3 (green), and 4 (cyan). (C) Group mean (bar) and individual (points) nose poke rate for all 20 sessions are shown. *independent samples t-test, p < 0.05.

Figure 2.. Timing of responding to Pavlovian fear conditioned cues.

(A) Mean suppression ratio is shown for the 14, 10-s intervals around shocklOO cue presentation for blocks 1 (magenta), 2, (brown), 3 (green), and 4 (cyan). Yellow vertical line and shock icon indicates time shock was delivered. (B) Group (bar) and individual (points) mean suppression ratios are shown for the first cue interval (left), pre shock interval (middle), and first post cue interval (right) during blocks 1–4. Females are black points and males are grey points. The three shaded regions in A correspond to the three trial periods in B. (C) Mean suppression ratio around shock50 presentation shown as in A. (D) Group (bar) and individual (points) mean suppression ratios shown as in B. +95% bootstrap confidence interval does not contain zero, each block is compared to block 1.

Figure 3.. Timing of cue responding following shock and correlated temporal responding.

(A) The diagram shows the post shock interval (closed bar) and last cue interval (open bar) for the shock50 cue. Yellow vertical line and shock icon indicate time shock was delivered. Females are black points and males are grey points. (B) Group (bar) and individu-al (points) mean suppression ratios are shown for the post shock cue interval (Ps, closed bar) and the last cue interval (Lc, open bar) during blocks 1 (magenta), 2, (brown), 3 (green), and 4 (cyan). (C) A correlation matrix was constructed for the five instances of tem-poral responding. Pearson’s correlation coefficient (R2) for each comparison is visualized from 0 (white) to 1 (black). *R² p-value < 0.005 (Bonferroni correction for 10 comparisons).