Contributions of the nucleus accumbens and its subregions to different aspects of risk-based decision making

Abstract

The nucleus accumbens (NAc) has been implicated in mediating different forms of decision making in humans and animals. In the present study, we observed that inactivation of the rat NAc, via infusion of GABA agonists, reduced preference for a large/risky option and increased response latencies on a probabilistic discounting task. Discrete inactivations of the NAc shell and core revealed further differences between these regions in mediating choice and response latencies, respectively. The effect on choice was attributable to reduced win-stay performance (i.e., choosing risky after a being rewarded for a risky choice on a preceding trial). Moreover, NAc inactivation altered choice only when the large/risky option had greater long-term value, in terms of the amount of food that could be obtained over multiple trials relative to the small/certain option. Inactivation of the NAc or the shell subregion also slightly reduced preference for larger rewards on a reward magnitude discrimination. Thus, the NAc seems to play a small role in biasing choice toward larger rewards, but its contribution to behavior is amplified when delivery of these rewards is uncertain, helping to direct response selection toward more favorable outcomes.

Dissociable Contributions by Prefrontal D1 and D2 Receptors to Risk-Based Decision Making

“…As was observed with analysis of overall choice behavior, this four-way interaction was driven by the fact that each drug induced a distinct effect on win-stay/lose-shift tendencies. With respect to win-stay performance, under control conditions, rats displayed a strong tendency (between 80 and 90%) to select the risky lever after selecting this lever on the preceding trial and receiving reward, as we have observed previously (Stopper and Floresco, 2011). Conversely, animals tended to shift to the small/certain lever following a "loss" after choosing the large/risky lever on ϳ25-30% of these trials under control conditions.…”

“…Reward magnitude discrimination task. As we have done previously (Ghods-Sharifi et al, 2009;Stopper and Floresco, 2011), we determined a priori that if a particular treatment specifically decreased preference for the large/risky lever on the probabilistic discounting task, separate groups of animals would be trained and tested on a reward magnitude discrimination task to determine whether this effect was due to an impairment in discriminating between reward magnitudes associated with the two levers. In these experiments, rats were trained to press retractable levers as in the probabilistic discounting task, after which they were trained on the discrimination task.…”

“…Thus, in either of these cases, the denominator in the equation used to compute these ratios would be zero for at least one of the blocks, which precluded us from conducting a block-by block analysis of these data. To overcome this, an analysis was conducted for all trials across the four blocks, as we have done previously (Stopper and Floresco, 2011). Changes in win-stay performance were used as a general index of the impact that obtaining the large, risky reward had on subsequent choice behavior, whereas changes in lose-shift performance served as an index of negative feedback sensitivity over the entire duration of the test session.…”

“…To obtain further insight into how these treatments affected patterns of choice and resulting alterations in discounting, we conducted a supplementary analysis of the choice data. Specifically, we conducted a choice-by-choice analysis to identify whether changes in behavior were due to alterations in the likelihood of choosing the risky lever after obtaining the larger reward (win-stay performance) or alterations in negative feedback sensitivity (lose-shift performance) (Bari et al, 2009;Stopper and Floresco, 2011). Animals' choices during the task were analyzed according to the outcome of each preceding free-choice trial (reward or non-reward) and expressed as a ratio.…”

Perturbations in Effort-Related Decision-Making Driven by Acute Stress and Corticotropin-Releasing Factor

“…For example, these treatments may have altered processes related to the objective valuation of different rewards and caused a more general impairment in preference for larger vs smaller rewards, as has been observed following inactivation of the nucleus accumbens shell or reducing GABA transmission in the prefrontal cortex (Stopper and Floresco, 2011;Piantadosi et al, 2016). To address this, we utilized a reward magnitude discrimination, equating the cost of the two lever options.…”