The Role of the Basal Ganglia in Executing and Learning Complex Motor Sequences

Abstract

We learn and perform precise motor sequences to interact with the environment. This ability underlies much of what we do, from playing musical instruments and using new tools to producing fluent speech. Understanding the neural circuits involved in producing these sequences is a central objective of the field of motor learning.

In this dissertation, I study the role of the basal ganglia in complex motor sequence learning and execution, and how they coordinate with the rest of the brain to fulfill both functions. First, I investigate whether the striatum is involved in complex sequence execution by lesioning the dorsolateral striatum (DLS, or sensorimotor striatum) and the dorsomedial striatum (DMS, or associative striatum) in rats trained to execute spatiotemporally precise lever-pressing sequences. Kinematics analysis revealed that DLS lesions significantly disrupted performance, while the DMS was largely dispensable for executing the motor skill. Next, I examined the role of the basal ganglia output in the same task by lesioning the globus pallidus interna (GPi). Third, I explored the role of the DLS and DMS in learning by lesioning the structures prior to training. DLS lesions severely disrupted learning in the task, whereas DMS lesions did not abort learning. Lastly, I examined the role of primary and secondary motor cortices in tutoring the basal ganglia by lesioning them before training. Both cortices have, to at least a degree, redundant functions with respect to learning the task. Overall, this dissertation suggests that the sensorimotor part of the basal ganglia is critical for both executing and learning complex motor sequences.