Arbitration between model-free and model-based control is not affected by transient changes in tonic serotonin levels

Area of Science:

• Neuroscience
• Cognitive Science
• Decision-Making Research

Background:

• Serotonin is implicated in decision-making, influencing the balance between model-based and model-free control.
• Dysregulation of these control mechanisms is linked to mental health conditions like drug dependence and obsessive-compulsive disorder.
• Previous research suggests low serotonin reduces model-based control, but the effect of increased serotonin remains unclear, as do the neural underpinnings.

Purpose of the Study:

• To determine if modulating tonic serotonin levels affects the arbitration between model-free and model-based control.
• To identify the neural mechanisms mediating any such effects.

Main Methods:

• A sequential two-stage Markov decision task was used with 98 participants in a randomized, double-blind, cross-over design.
• A tryptophan intervention (loading, balanced, depletion) was employed to manipulate serotonin levels.
• Functional magnetic resonance imaging (fMRI) was utilized to measure brain responses.

Main Results:

• No significant effect of altered tonic serotonin levels on either model-free or model-based control was observed.
• The tryptophan intervention did not lead to significant changes in Blood-Oxygenation-Level Dependent (BOLD) activity in the brain.

Conclusions:

• Tonic serotonin levels do not appear to play a critical role in modulating the balance between model-based and model-free decision-making control.
• The tested serotonergic manipulation did not alter neural activity associated with these control mechanisms.