Reward value and internal state differentially drive impulsivity and motivation

Abstract

Goal-directed behavior is influenced by both reward value as well as internal state. A large body of research has focused on how reward value and internal drives such as hunger influence motivation in rodent models, however less work has focused on how these factors may differentially affect impulsivity. In these studies, we tested the effect of internal drive versus reward value on different facets of reward-related behavior including impulsive action, impulsive choice and, motivation. We varied reward value by changing the concentration of sucrose in the reward outcome, and varied internal drive by manipulating thirst through water restriction. Consistent with the literature we found that both internal state and reward value influenced motivation. However, we found that in high effort paradigms, only internal state influenced motivation with minimal effects of reward value. Interestingly, we found that internal state and reward value differentially influence different subtypes of impulsivity. Internal state, and to a lesser extent, reward value, influenced impulsive action as measured by premature responding. On the other hand, there were minimal effects of either reward value or homeostatic state on impulsive choice as measured by delay discounting. Overall, these studies begin to address how internal state and reward value differentially drive impulsive behavior. Understanding how these factors influence impulsivity is important for developing behavioral interventions and treatment targets for patients with dysregulated motivated or impulsive behavior.

Keywords: Goal directed behavior; Impulsivity; Internal state; Motivation; Reward value.

Figure 1.. Reward value and internal drive influence impulsive action.

A) A diagram of the 2-choice serial reaction time task (2CSRTT) operant paradigm used to measure impulsive action is shown. B) The number of trials initiated is shown during 2CSRTT averaged across the three delay lengths over the three reward conditions. C) The total number of premature responses (port entries during the delay window) normalized by the number of trials initiated is shown over three delay lengths in the three reward conditions. D) The percentage of trials rewarded is shown over three delay lengths in the three reward conditions. Graphs display individual animals (dots) and group averages (bars) ± SEM for the 3 reward conditions: 5% sucrose (N=11, 5M/6F), Water (N=18,11M/7F), and 5% sucrose with supplemental water (N=13, 6M/7F).

Figure 2.. No effect of reward value or internal drive on delay discounting.

A) A diagram of the delay discounting operant paradigm used to measure impulsive choice is shown. B) The number of trials initiated averaged across all 6 delay lengths are shown for the three reward conditions. C) Preference for the large reward port is shown across six delay lengths in the three reward conditions. Graphs display individual animals (dots) and group averages (bars) ± SEM for the 3 reward conditions: 5% sucrose (N=11, 5M/6F), Water (N=12,6M/6F), and 5% sucrose with supplemental water (N=12, 6M/6F).

Figure 3.. Reducing internal drive, but not reward value, decreases motivation at high effort requirements.

A) A diagram of the operant paradigms are shown. The number of rewards earned is shown for the three groups of mice across three random ratio schedules (B) and one progressive ratio (C) schedule. Graphs display individual animals (dots) and group averages (bars) ± SEM for the 3 reward conditions for RR: 5% sucrose (N=11, 5M/6F), Water (N=14,10M/4F), and 5% sucrose with supplemental water (N=12, 6M/6F); or PR 5% sucrose (N=7, 4M/3F), Water (N=7,4M/3F), and 5% sucrose with supplemental water (N=6, 3M/3F). *p<0.05