How do the basal ganglia contribute to categorization? Their roles in generalization, response selection, and learning via feedback

Abstract

This article examines how independent corticostriatal loops linking basal ganglia with cerebral cortex contribute to visual categorization. The first aspect of categorization discussed is the role of the visual corticostriatal loop, which connects the visual cortex and the body/tail of the caudate, in mapping visual stimuli to categories, including evaluating the degree to which this loop may generalize across individual category members. The second aspect of categorization discussed is the selection of appropriate actions or behaviors on the basis of category membership, and the role of the visual corticostriatal loop output and the motor corticostriatal loop, which connects motor planning areas with the putamen, in action selection. The third aspect of categorization discussed is how categories are learned with the aid of feedback linked dopaminergic projections to the basal ganglia. These projections underlie corticostriatal synaptic plasticity across the basal ganglia, and also serve as input to the executive and motivational corticostriatal loops that play a role in strategic use of feedback.

Figure 1

Main pathways through the basal ganglia. GPe: Globus pallidus, external portion. GPi: Globus pallidus, internal portion. SNr: Substantia nigra pars reticulata. SNc: Substantia nigra pars compacta. STN: Subthalamic nucleus. VTA: Ventral tegmental area.

Figure 2

Four primary corticostriatal loops. GPi: Globus pallidus, internal portion. SNr: Substantia nigra pars reticulata.

Figure 3

Tasks and results from three studies of categorization. Top row: Sample stimuli from each task. Middle row: Areas of activity in the body and tail of the caudate during correct classification of stimuli. Bottom row: Areas affected by feedback processing.