Contributions of medial prefrontal cortex to decision making involving risk of punishment

Abstract

The prefrontal cortex (PFC) plays an important role in several forms of cost-benefit decision making. Its contributions to decision making under risk of explicit punishment, however, are not well understood. A rat model was used to investigate the role of the medial PFC (mPFC) and its monoaminergic innervation in a Risky Decision-making Task (RDT), in which rats chose between a small, "safe" food reward and a large, "risky" food reward accompanied by varying probabilities of mild footshock punishment. Inactivation of mPFC increased choice of the large, risky reward when the punishment probability increased across the session ("ascending RDT"), but decreased choice of the large, risky reward when the punishment probability decreased across the session ("descending RDT"). In contrast, enhancement of monoamine availability via intra-mPFC amphetamine reduced choice of the large, risky reward only in the descending RDT. Systemic administration of amphetamine reduced choice of the large, risky reward in both the ascending and descending RDT; however, this reduction was not attenuated by concurrent mPFC inactivation, indicating that mPFC is not a critical locus of amphetamine's effects on risk taking. These findings suggest that mPFC plays an important role in adapting choice behavior in response to shifting risk contingencies, but not necessarily in risk-taking behavior per se.

Keywords: Decision making; Medial prefrontal cortex; Monoamine; Punishment; Risk.

Figure 1.. Experiment 1: Effects of mPFC inactivation on risky decision making.

A. Cannula placements in the mPFC in Experiment 1.1. Black circles denote locations of the tips of the injectors used for microinjections. B. Inactivation of the mPFC with microinjection of baclofen/muscimol during the RDT with ascending punishment probabilities caused a significant increase in choice of the large, risky reward. C. Cannula placements in the mPFC in Experiment 1.2. D. Inactivation of the mPFC during the RDT with descending punishment probabilities caused a significant decrease in choice of the large, risky reward. Data are represented as the mean ± SEM (within subjects) percent choice of the large, risky reward.

Figure 2.. Experiment 2: Effects of mPFC amphetamine on risky decision making.

A. Cannula placements in the mPFC in Experiment 2.1. Black circles denote locations of the tips of the injectors used for microinjections. B. Microinjections of amphetamine in the mPFC had no effect on choice of the large, risky reward in the RDT with ascending punishment probabilities. C. Cannula placements in the mPFC in Experiment 2.2. D. Microinjections of amphetamine in the mPFC caused a significant decrease in choice of the large, risky reward in the RDT with descending punishment probabilities, with the 10 μg dose differing significantly from vehicle. Data are represented as the mean ± SEM (within subjects) percent choice of the large, risky reward.

Figure 3.. Experiment 3: Effects of mPFC inactivation on systemic amphetamine-induced risk aversion.

A. Cannula placements in the mPFC in Experiment 3.1. Black circles denote locations of the tips of the injectors used for microinjections. B. In the RDT with ascending punishment probabilities, mPFC inactivation caused a significant increase in choice of the large, risky reward and systemic amphetamine caused a significant decrease in choice of the large, risky reward, but mPFC inactivation did not alter the effects of amphetamine. C. Cannula placements in the mPFC in Experiment 3.2. D. In the RDT with descending punishment probabilities, systemic amphetamine caused a significant decrease in choice of the large, risky reward, but mPFC inactivation did not alter the effects of amphetamine. Data are represented as the mean ± SEM (within subjects) percent choice of the large, risky reward.