Independent circuits in the basal ganglia for the evaluation and selection of actions

Abstract

The basal ganglia are critical for selecting actions and evaluating their outcome. Although the circuitry for selection is well understood, how these nuclei evaluate the outcome of actions is unknown. Here, we show in lamprey that a separate evaluation circuit, which regulates the habenula-projecting globus pallidus (GPh) neurons, exists within the basal ganglia. The GPh neurons are glutamatergic and can drive the activity of the lateral habenula, which, in turn, provides an indirect inhibitory influence on midbrain dopamine neurons. We show that GPh neurons receive inhibitory input from the striosomal compartment of the striatum. The striosomal input can reduce the excitatory drive to the lateral habenula and, consequently, decrease the inhibition onto the dopaminergic system. Dopaminergic neurons, in turn, provide feedback that inhibits the GPh. In addition, GPh neurons receive direct projections from the pallium (cortex in mammals), which can increase the GPh activity to drive the lateral habenula to increase the inhibition of the neuromodulatory systems. This circuitry, thus, differs markedly from the "direct" and "indirect" pathways that regulate the pallidal (e.g., globus pallidus) output nuclei involved in the control of motion. Our results show that a distinct reward-evaluation circuit exists within the basal ganglia, in parallel to the direct and indirect pathways, which select actions. Our results suggest that these circuits are part of the fundamental blueprint that all vertebrates use to select actions and evaluate their outcome.striosomes | reward/aversion | pallium/cortex | evolution T o achieve a goal, animals need to select actions and evaluate their outcome to determine whether their goal was achieved. In mammals, the basal ganglia play a key role in the selection of actions (1-3) and have more recently been suggested to additionally contribute to predicting and evaluating the outcome of the selected actions (4-8).The so-called "direct" and "indirect" pathways through the basal ganglia are present in all vertebrates and act together to select actions by decreasing tonic inhibition of the basal ganglia output nuclei [globus pallidus interna (GPi) and substantia nigra pars reticulata (SNr)] on a selected motor program and increasing the inhibition onto other competing actions. The output of these selection circuits target brainstem and thalamic motor areas, and neurons within this circuit are modulated by various aspect of movement kinetics related to the initiation and modulation of ongoing actions.In addition to the output neurons that project to motor areas, a separate subpopulation of pallidal neurons projects to the lateral habenula (9-12), a structure involved in evaluating and predicting the motivational value of actions. Recent in vivo recordings in primates have shown that the activity of these habenula-projecting pallidal neurons is modulated by the cues that predict the availability of reward (13,14) and not by aspects of movements. The majority of these pallidal neurons, as with latera...

Homology versus Convergence in Resolving Transphyletic Correspondences of Brain Organization

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