Acute stress facilitates habitual behavior in female rats

Abstract

Instrumental behavior can reflect the influence of goal-directed and habitual systems. Contemporary research suggests that stress may facilitate control by the habitual system under conditions where the behavior would otherwise reflect control by the goal-directed system. However, it is unclear how stress modulates the influence of these systems on instrumental responding to achieve this effect, particularly in females. Here, we examine whether a mild psychogenic stressor experienced before acquisition training (Experiment 1), or prior to the test of expression (Experiment 2) would influence goal-directed and habitual control of instrumental responding in female rats. In both experiments, rats acquired an instrumental nose-poke response for a sucrose reward. This was followed by a reinforcer devaluation phase in which half the rats in Stressed and Non-Stressed conditions received pairings of the sucrose pellet with illness induced by lithium chloride until they rejected the pellet when offered. The remaining rats received a control treatment consisting of pellets and illness on separate days (Unpaired). Control by goal-directed and habitual systems was evaluated in a subsequent nonreinforced test of nose poking. The results of Experiment 1 indicated that the Non-Stressed Paired group reduced nose-poking compared to the Unpaired controls, identifying the response as goal directed, whereas the Stressed Paired and Unpaired groups made a similar number of nose pokes identifying the response as habitual despite a similar amount of training. Results from Experiment 2 indicated habitual control of nose-poke responding was present when stress was experienced just prior to the test. Collectively, these data suggest that stress may facilitate habitual control by altering the relative influence of goal-directed and habitual processes underpinning instrumental behavior. These results may be clinically relevant for understanding the contributions of stress to dysregulated instrumental behavior in compulsive pathologies.

Keywords: Action sequences; Females, Reinforcer devaluation; Goal-directed action; Habit; Stress.

Figure 1.. Experimental Timeline

Note. A) Experimental timeline for Experiment 1: Stress before acquisition. B) Experimental timeline for Experiment 2: Stress before test.

Figure 2.. Results of Experiment 1

Note. A) Mean nose-poke rates (responses per minute) over the two sessions of training on a VI 30-s schedule. B) Mean number of sucrose pellets consumed by Paired condition animals during each cycle of the outcome devaluation phase. C) Mean nose-poke rates during the test as a proportion of nose-poke rate in the final VI 30-s session (proportion of baseline). D) Mean food-cup entry rates during the test as a proportion of baseline. E) Mean nose-pokes per minute during the reacquisition test as a proportion of baseline. Error bars denote standard error of the mean.

Figure 3.. Results of Experiment 1 response sequence analyses

Note. A) Graphic depicting independent nose-poke responses and nose-poke to food-cup entry sequences. B) Mean nonreinforced (NR) independent nose-poke responses per minute during the final VI 30-s training session. C) Mean NR nose-poke to food-cup entry sequences per minute during the final VI 30-s training session. D) Mean independent nose-poke responses per minute during the test as a proportion of the independent response rates from the final VI 30-s training session (proportion of baseline). E) Mean nose-poke to food-cup entry sequences as a proportion of mean sequence rate in the final VI 30-s training session (proportion of baseline). Error bars denote standard error of the mean.

Figure 4.. Results of Experiment 2

Note. A) Mean nose-poke rates (responses per minute) in the two VI 30-s training sessions. B) Mean number of sucrose pellets consumed by Paired condition animals during each cycle of the outcome devaluation phase. C) Mean nose-poke rates during the test as a proportion of nose-poke rate in the final VI 30-s training session (proportion of baseline). D) Mean food-cup entries per minute during the test as a proportion food-cup rates in the final VI 30-s training session. E) Mean nose-pokes per minute during the reacquisition test as a proportion of baseline. Error bars denote standard error of the mean.

Figure 5.. Results of Experiment 2 response sequence analyses

Note. A) Mean NR independent nose-poke responses per minute during in the final VI 30-s training session. B) Mean NR nose-poke to food-cup entry sequences per minute during the final VI 30-s training session. C) Mean independent nose-poke responses per minute during the test as a proportion of baseline independent response rates from the final VI 30-s training session. D) Mean nose-poke to food-cup entry sequences as a proportion of baseline sequence rates from the final VI 30-s training session. Error bars denote standard error of the mean.