Abstract

A typical Go/No-Go decision is suggested to be implemented in the brain via the activation of the direct or indirect pathway in the basal ganglia. Medium spiny neurons (MSNs) in the striatum, receiving input from cortex and projecting to the direct and indirect pathways express D1 and D2 type dopamine receptors, respectively. Recently, it has become clear that the two types of MSNs markedly differ in their mutual and recurrent connectivities as well as feedforward inhibition from FSIs. Therefore, to understand striatal function in action selection, it is of key importance to identify the role of the distinct connectivities within and between the two types of MSNs on the balance of their activity. Here, we used both a reduced firing rate model and numerical simulations of a spiking network model of the striatum to analyze the dynamic balance of spiking activities in D1 and D2 MSNs. We show that the asymmetric connectivity of the two types of MSNs renders the striatum into a threshold device, indicating the state of cortical input rates and correlations by the relative activity rates of D1 and D2 MSNs. Next, we describe how this striatal threshold can be effectively modulated by the activity of fast spiking interneurons, by the dopamine level, and by the activity of the GPe via pallidostriatal backprojections. We show that multiple mechanisms exist in the basal ganglia for biasing striatal output in favour of either the `Go' or the `No-Go' pathway. This new understanding of striatal network dynamics provides novel insights into the putative role of the striatum in various behavioral deficits in patients with Parkinson's disease, including increased reaction times, L-Dopa-induced dyskinesia, and deep brain stimulation-induced impulsivity.

Highlights

  • The basal ganglia (BG) are a set of nuclei, located at the base of the forebrain, which play a crucial role in a variety of motor and cognitive functions

  • To understand the computations performed by the basal ganglia, it is of key importance to characterize the dynamical properties of striatal network activity

  • We show that the firing rates of both D1 and D2 medium spiny neurons (MSNs) change in a non-monotonic manner in response to cortical input rates and correlations

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Summary

Introduction

The basal ganglia (BG) are a set of nuclei, located at the base of the forebrain, which play a crucial role in a variety of motor and cognitive functions. The striatum is the main input stage of the basal ganglia, receiving inputs from widely distributed areas in the cortex [1], and projecting to the BG output nuclei Globus Pallidus Interna (GPi) and Substantia Nigra (SNr) via the so-called direct and indirect pathways, respectively [2]. A complete shutdown of activity in either of the two neuron subpopulations might not occur in awake behaving animals [8]. In such a scenario,though, action selection could still be performed by a relative increase in the activity of one subpopulation compared to the other

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