Category: Neurophysiology (Non-PD)
Objective: The basal ganglia (BG) are known to play a vital role in action initiation and inhibition, studied with several simple behaviors in multiple species. While the human STN has been studied, the remaining nodes in this circuitry in humans are unexplored. We sought to determine how the BG encode action execution and confidence in ongoing actions.
Background: In classic BG models, the GPi tonically inhibits thalamocortical projections preventing movement.[1,2] GPi can be directly inhibited by the striatum or indirectly via GPe excitation, leading to movement. However, in rodents, distinct neural populations in the GPe promote movement initiation or suppression [3-5] and the striatal direct and indirect pathways are both active at the onset of movements; inhibition of either can abort action sequences. The STN was thought to inhibit movements[8-11], but in non-human primates, STN neurons encode action initiation, inhibition, and changes in action plans [12-14]. We hypothesized that movement plans and the confidence in whether an ongoing plan of action should continue is encoded throughout neural populations in the BG.
Method: We performed microelectrode recordings while patients (n=10) with Parkinson’s disease or essential tremor completed a decision-making task during DBS surgery. Patients performed reaching movements to one of four targets indicating their choice and confidence about a visual stimulus [figure1]. Spiking neuron data was obtained from the STN (n=44), ventrooralis (Vo, n=18) and ventral intermediate (Vim, n=20) thalamic nuclei, GPi (n=10), and GPe (n=26).
Results: Reaching movements were preceded by slowly ramping spiking activity in Vo and by a sharp increase in Vim [figure2]. Surprisingly, GPe and GPi spiking activity increased during distinct phases of movement preparation. Low confidence movements were encoded by increased firing rates across the Vim neuronal population and in individual STN neurons [figure3]. In contrast, individual GPe neurons had decreased firing rates for low confidence movements. We found neurons responsive to the outcome of each trial, with neurons in Vo encoding reward prediction errors [figure4].
Conclusion: Neuronal encoding of movements in human basal ganglia and thalamus contradict predictions of BG models. Confidence in ongoing actions and responses to their outcomes is encoded throughout multiple nodes in this circuit.
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To cite this abstract in AMA style:D. London, M. Soula, L. Pan, R. Kiani, A. Mogilner. Encoding of action plans and confidence in the human basal ganglia-thalamic circuit [abstract]. Mov Disord. 2023; 38 (suppl 1). https://www.mdsabstracts.org/abstract/encoding-of-action-plans-and-confidence-in-the-human-basal-ganglia-thalamic-circuit/. Accessed September 27, 2023.
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MDS Abstracts - https://www.mdsabstracts.org/abstract/encoding-of-action-plans-and-confidence-in-the-human-basal-ganglia-thalamic-circuit/