Exploration and Exploitation of Action Selection in the Motor Cortex and Basal Ganglia.

Abstract

The basal ganglia (BG) have been proposed as a possible neural substrate for action selection in the vertebrate brain. In this thesis, I have focused on determining the role of BG circuits in selection of well-trained actions, and how these findings can be applied for use in neuroprosthetic devices.

In the first study, I investigated one proposed mechanism to help resolve competition between actions in the BG: feedforward inhibition of striatal medium spiny cells (MSNs) by fast-spiking interneurons (FSIs). I recorded single unit activity from pre- sumed MSNs and FSIs together with motor cortex and globus pallidus (GP), in rats performing a simple choice task. My findings support the idea that FSIs contribute to action selection processes within striatal microcircuits.

In my second study, I examined the role of large neuronal ensembles of the BG and motor cortex during two variations on a simple action selection task. Analysis of local field potential (LFP) oscillations revealed that ∼20Hz rhythms (β20) were prominent during the hold period, but only if subjects were instructed on which direction to move during the hold period. This finding is consistent with the hypothesis that β20 is involved with the selection of actions.

In the third study, I examined how action selection circuitry can be exploited to aid in the development of a neuroprosthetic system. By bypassing injured neurons, we can allow for direct motor control from non-injured neurons. I developed an algorithm that observes the pattern of activity in cortical ensembles and allows both the subjects and control system to co-adapt their behavior to allow na ̈ıve rats to use a neuroprosthetic device. The results of this study show that subjects can learn to select discrete actions in real-time using the neural activity of the cortex.

In this thesis, I investigated action selection at the single-unit and multi-unit levels, while studying neural ensembles both within and across brain structures. Further knowledge in this field will help solve neurological diseases and yield more sophisticated, yet more natural control of neuroprosthetic devices which will rely on native BG and cortical roles in action selection.