Synchronization and exploration in basal ganglia—A spiking network model

Abstract

Making an optimal decision could be to either ‘Explore’ or ‘exploit’ or ‘not to take any action,’ and basal ganglia (BG) are considered to be a key neural substrate in decision making. In earlier chapters, we had hypothesized earlier that the indirect pathway (IP) of the BG could be the subcortical substrate for exploration. Here, we build a spiking network model to relate exploration to synchrony levels in the BG (which are a neural marker for tremor in Parkinson’s disease). Key BG nuclei such as the subthalamic nucleus (STN), Globus Pallidus externus (GPe), and Globus Pallidus internus (GPi) were modeled as Izhikevich spiking neurons, whereas the striatal output was modeled as Poisson spikes. We have applied reinforcement learning framework with the dopamine signal representing the reward prediction error used for cortico-striatal weight update. We apply the model to two decision-making tasks: a binary action selection task and an n-armed bandit task. The model shows that exploration levels could be controlled by STN’s lateral connection strength which also influenced the synchrony levels in the STN–GPe circuit. An increase in STN’s lateral strength led to a decrease in exploration which can be thought as the possible explanation for reduced exploratory levels in Parkinson’s patients.