Fatigue modulates dopamine availability and promotes flexible choice reversals during decision making

Pierpaolo Iodice,Giovanni Pezzulo,Feliciano Protasi,Mark E Walton,Luigi Brunetti,Simona Cabib,Claudio Ferrante

doi:10.1038/s41598-017-00561-6

Abstract

During decisions, animals balance goal achievement and effort management. Despite physical exercise and fatigue significantly affecting the levels of effort that an animal exerts to obtain a reward, their role in effort-based choice and the underlying neurochemistry are incompletely known. In particular, it is unclear whether fatigue influences decision (cost-benefit) strategies flexibly or only post-decision action execution and learning. To answer this question, we trained mice on a T-maze task in which they chose between a high-cost, high-reward arm (HR), which included a barrier, and a low-cost, low-reward arm (LR), with no barrier. The animals were parametrically fatigued immediately before the behavioural tasks by running on a treadmill. We report a sharp choice reversal, from the HR to LR arm, at 80% of their peak workload (PW), which was temporary and specific, as the mice returned to choose the HC when the animals were successively tested at 60% PW or in a two-barrier task. These rapid reversals are signatures of flexible choice. We also observed increased subcortical dopamine levels in fatigued mice: a marker of individual bias to use model-based control in humans. Our results indicate that fatigue levels can be incorporated in flexible cost-benefits computations that improve foraging efficiency.

Highlights

In both the wild and the laboratory, animals’ preferences for one course of action over another reflect both the value of action goals and the cost or effort that must be invested in pursuing them
Consider the case of a rodent in a T-maze choosing between a high-reward option (HR) that can only be obtained at high cost by climbing over a barrier, and a low-reward, low-cost option (LR) where the reward is available in an otherwise unoccupied arm of the maze
To test the predictions of these contrasting views, we parametrically varied the level of fatigue of a population of mice that performed a series of effort-based T-maze tasks (HR vs. low-reward arm (LR)) with one barrier on the HR branch, and a double-barrier task with barriers on both HR and LR branches[18]

Summary

Introduction

In both the wild and the laboratory, animals’ preferences for one course of action over another reflect both the value of action goals and the cost or effort that must be invested in pursuing them. One should expect that physical effort might generically impair choice performance (e.g., make it more random) Another stream of research reveals that mental effort induces humans to use less demanding, automatic or habitual (model-free) control strategies rather than more demanding and more flexible (model-based) strategies based on cognitive planning[12]. The cost-benefit analysis hypothesis would predict an opposite preference reversal (from LR to HR) when fatigued animals face a double-barrier task, which imposes the same costs on both branches Of note, this normative (cost-benefit) perspective has to be carefully teased apart carefully from a seemingly related possibility: that fatigue affects decision-making by inducing Pavlovian avoidance/aversion bias[16, 17] (e.g., a bias to avoid costly actions such as climbing barriers). To test the predictions of these contrasting views, we parametrically varied the level of fatigue (from “no fatigue” to 40%, 60% and 80% of maximal workload of each specific animal) of a population of mice that performed a series of effort-based T-maze tasks (HR vs. LR) with one barrier on the HR branch, and a double-barrier task with barriers on both HR and LR branches[18]

Methods

Results

Conclusion