No substantial change in the balance between model-free and model-based control via training on the two-step task.

Elmar D Grosskurth,Dominik R Bach,Marcos Economides,Quentin J M Huys,Lisa Holper

doi:10.1371/journal.pcbi.1007443

Abstract

Human decisions can be habitual or goal-directed, also known as model-free (MF) or model-based (MB) control. Previous work suggests that the balance between the two decision systems is impaired in psychiatric disorders such as compulsion and addiction, via overreliance on MF control. However, little is known whether the balance can be altered through task training. Here, 20 healthy participants performed a well-established two-step task that differentiates MB from MF control, across five training sessions. We used computational modelling and functional near-infrared spectroscopy to assess changes in decision-making and brain hemodynamic over time. Mixed-effects modelling revealed overall no substantial changes in MF and MB behavior across training. Although our behavioral and brain findings show task-induced changes in learning rates, these parameters have no direct relation to either MF or MB control or the balance between the two systems, and thus do not support the assumption of training effects on MF or MB strategies. Our findings indicate that training on the two-step paradigm in its current form does not support a shift in the balance between MF and MB control. We discuss these results with respect to implications for restoring the balance between MF and MB control in psychiatric conditions.

Highlights

Decision-making is suggested to rely on at least two parallel and distinct systems; a retrospectively-driven system based on acquired habits, and a prospective goal-directed system based on deliberate planning [1,2,3,4,5,6,7]
Our results suggest that training on the current form of the two-step task does not support a shift in the balance between model-free and model-based strategies
The current study was conducted in healthy subjects and may not be directly generalizable to psychiatric populations with premorbid, i.e., pre-training, deficits in MB control, our results may contribute to the current debate how the two-step could be adjusted to be used as training tool and to advance its application in the trans-diagnostic evaluation of psychiatric conditions [43,67]

Summary

Introduction

Decision-making is suggested to rely on at least two parallel and distinct systems; a retrospectively-driven system based on acquired habits, and a prospective goal-directed system based on deliberate planning [1,2,3,4,5,6,7]. Goal-directed behavior requires the consideration of potential future outcomes of alternative actions based on the implementation of planned actions and outcomes. In computational terms, these two strategies are described as model-free (MF) and model-based (MB) decision control [1,2,11], respectively. These two strategies are often thought to be employed in parallel but the arbitration between them as determined by situations, actions and outcomes, has to be learned by exploration of the statetransition prediction error [12]

Objectives

Results

Discussion

Conclusion