Pallidal neuromodulation of the explore/exploit trade-off in decision-making

Every decision that we make involves a conflict between exploiting our current knowledge of an action’s value or exploring alternative courses of action that might lead to a better, or worse outcome. The sub-cortical nuclei that make up the basal ganglia have been proposed as a neural circuit that may contribute to resolving this explore-exploit ‘dilemma’. To test this hypothesis, we examined the effects of neuromodulating the basal ganglia’s output nucleus, the globus pallidus interna, in patients who had undergone deep brain stimulation (DBS) for isolated dystonia. Neuromodulation enhanced the number of exploratory choices to the lower value option in a 2-armed bandit probabilistic reversal-learning task. Enhanced exploration was explained by a reduction in both rate of evidence accumulation (drift rate) and by the amount of evidence needed to decide (boundary separation) in a reinforcement learning drift diffusion model. We estimated the functional connectivity profile between the stimulating DBS electrode and the rest of the brain using a normative functional connectome derived from heathy controls. Variation in the extent of neuromodulation induced exploration between patients was predicted by the degree of functional connectivity between the stimulating electrode and prefrontal and sensorimotor cortices. We conclude that the basal ganglia’s output nucleus, the globus pallidus interna, can adaptively modify decision choice when faced with the dilemma to explore or exploit.