Reward/Punishment-Based Decision Making in Rodents

Abstract

Deficits in decision making are at the heart of many psychiatric diseases, such as substance abuse disorders and attention deficit hyperactivity disorder. Consequently, rodent models of decision making are germane to understanding the neural mechanisms underlying adaptive choice behavior and how such mechanisms can become compromised in pathological conditions. A critical factor that must be integrated with reward value to ensure optimal decision making is the occurrence of consequences, which can differ based on probability (risk of punishment) and temporal contiguity (delayed punishment). This article will focus on two models of decision making that involve explicit punishment, both of which recapitulate different aspects of consequences during human decision making. We will discuss each behavioral protocol, the parameters to consider when designing an experiment, and finally how such animal models can be utilized in studies of psychiatric disease. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Behavioral training Support Protocol: Equipment testing Alternate Protocol: Reward discrimination Basic Protocol 2: Risky decision-making task (RDT) Basic Protocol 3: Delayed punishment decision-making task (DPDT).

Keywords: decision making; delay; discounting; punishment; rat; reward; reward/punishment; risk.

Figure 1.. Coulbourn operant chamber.

The Risky Decision-making Task can be conducted in a Coubourn operant chamber (Orsini et al., 2016; Simon et al., 2009). Each chamber consists of two metal side walls, Plexiglass front and back walls and a stainless-steel grid floor through which footshocks are delivered. The chamber is equipped with a recessed food trough (not shown) and two retractable levers positioned to the left and right of the trough. Food is delivered via a food hopper located directly above the food trough. A house light is located on the top left part of the control board (“Environmental Control Board”) located directly behind the operant chamber. Finally, an activity monitor is attached to the top of the chamber to detect locomotor activity in the chamber below.

Figure 2.. Med Associates operant chamber.

Both the Risky Decision-making Task and the Delayed Punishment Decision-making Task have been conducted using this operant chamber format (Freels et al., 2020; Liley et al., 2019). Each chamber consists of two metal side walls, Plexiglass front and back walls and a stainless-steel grid floor through which footshocks are delivered. The chamber is equipped with a recessed food trough and retractable levers positioned to the left and right of the trough (trough pictured is extra tall to enable unimpeded entry with a cranial implant). Food is delivered via a food hopper located directly above the food trough. A house light is located on the top central part of the back wall of the chamber. Finally, activity monitors are attached to both plexiglass walls. The control board is located in the bottom corner behind the front wall (not shown).

Figure 3.. Representation of a free choice trial in the Risky Decision-making Task.

A. At the start of each trial, the food trough light is illuminated. B. A poke into the lit trough causes both levers to extend. Rats choose between the two levers, causing both to retract. C. Choice of the left lever results in immediate delivery of a single pellet, with no other programmed consequences (small, “safe” reward). D. Choice of the right lever results in immediate delivery of three pellets accompanied by increasing probabilities of footshock punishment (large, “risky” reward). After either lever press sequence, the trial progresses to the intertrial interval, and then repeats.

Figure 4.. Representation of stable behavior in the Risky Decision-making Task.

On average, as the risk of punishment increases across the behavioral test session, the choice of the large, risky reward decreases. Data are represented as mean choice of the large, risky reward ± standard error of the mean.

Figure 5.. Representation of a free choice trial in the Delayed Punishment Decision-making Task.

A. At the start of each trial, the food trough light is illuminated. B. A poke into the lit trough causes both levers to extend. Rats choose between the two levers, causing both to retract. C. Choice of the left lever results in immediate delivery of a single pellet, followed by a delay period that varies based on trial block. D. Choice of the right lever results in immediate delivery of three pellets, followed by a delay period, then a one second footshock. Delays are comparable for each lever, and increase throughout the session. After either lever press sequence, the trial progresses to the intertrial interval, and then repeats.

Figure 6.. Representation of stable behavior in the Delayed Punishment Decision-making Task.

On average, rats shift choice toward the punished reward as the delay increases, indicative of underestimation of delayed punishment. Data are represented as mean choice of the large, punished reward ± standard error of the mean. NS = No Shock.