Foot shock facilitates reward seeking in an experience-dependent manner

Abstract

Animals organize reward seeking around aversive events. An abundance of research shows that foot shock, as well as a shock-associated cue, can elicit freezing and suppress reward seeking. Yet, there is evidence that experience can flip the effect of foot shock to facilitate reward seeking. Here we examined cue suppression, foot shock suppression and foot shock facilitation of reward seeking in a single behavioural setting. Male Long Evans rats received fear discrimination consisting of danger, uncertainty, and safety cues. Discrimination took place over a baseline of rewarded nose poking. With limited experience (1-2 sessions), all cues and foot shock suppressed reward seeking. With continued experience (10-16 sessions), suppression became specific to shock-associated cues, foot shock briefly suppressed, then facilitated reward seeking. Our results provide a means of assessing positive properties of foot shock, and may provide insight into maladaptive behaviour around aversive events.

Keywords: Fear discrimination; Foot shock; Opponent process; Reward; Transfer.

Figure 1.

Experimental outline and session by session nose poking. Trial schematic showing the four periods of interest for danger (red), uncertainty (purple) and safety (blue) trial types (A). Mean +SEM nose poke rate in each session of fear discrimination during baseline (B), cue (C), immediate post shock (D), and delay post shock (E) periods. Gray bar, baseline; yellow bar, foot shock. Error bars show +SEM.

Figure 2.

Differential nose poking on shock and omission trials over sessions. Mean +SEM differential nose poke rate across sessions of fear discrimination: uncertainty-omission trials subtracted from uncertainty-shock (purple), safety trials subtracted from danger trials (red), during baseline (A), cue (B), immediate post shock (C), and delay post shock (D) periods. ⁺95% bootstrap confidence interval does not contain zero.

Figure 3.

Nose poking in 1 s intervals around cue and shock. Mean +SEM nose poke rate during 1 s interval: 2 s baseline → 10 s cue (A), 10 s post shock (B). Solid box indicates immediate post shock period, dashed box indicates delay post shock period. Baseline subtracted nose poke rate for each subject shown for each trial type (D = danger, U-S = uncertainty-shock, U-O = uncertainty-omission, S = safety), during cue (C), immediate (D), and delay (E) periods. ⁺95% bootstrap confidence interval does not contain zero.

Figure 4.

Differential nose poking on shock and omission trials in 1 s intervals around cue and shock. Mean +SEM differential nose poke rate during 1 s interval: 2 s baseline → 10 s cue (A), 10 s post shock (B). Safety subtracted from danger (D/S, red) and uncertainty-omission subtracted from uncertainty-shock (U-S/U-O, purple). Solid box indicates immediate post shock period, dashed box indicates delay post shock period. Differential nose poke rate for each subject shown for each period: cue (C), immediate post shock (D), and immediate delay (E) periods. ⁺95% bootstrap confidence interval does not contain zero.

Figure 5.

Relationships between foot shock facilitation and other aspects of behaviour. Mean differential nose poke rates for each subject during uncertainty-shock trials (uncertainty-shock minus baseline, upper panels), and danger trials (danger minus baseline, lower panels), compared to the baseline period (A-B), danger safety discrimination (danger minus safety, C-D), and immediate post shock period (immediate post shock minus baseline, E-F). Mean differential nose poke rates for each subject during uncertainty-shock trials (uncertainty-shock minus baseline, upper panels), and danger trials (danger minus baseline, lower panels), compared to one another (G).