Abstract
Basal ganglia (BG) can either facilitate or inhibit movement through excitatory and inhibitory pathways; however whether these opposing signals are dynamically regulated during healthy behavior is not known. Here, we present compelling neurophysiological evidence from three complimentary experiments in non-human primates, indicating task-specific changes in tonic BG pathway weightings during saccade behavior with different cognitive demands. First, simultaneous local field potential recording in the subthalamic nucleus (STN; BG input) and substantia nigra pars reticulata (SNr; BG output) reveals task-dependent shifts in subthalamo-nigral signals. Second, unilateral electrical stimulation of the STN, SNr, and caudate nucleus results in strikingly different saccade directionality and latency biases across the BG. Third, a simple artificial neural network representing canonical BG signaling pathways suggests that pathway weightings can be altered by cortico-BG input activation. Overall, inhibitory pathways (striato-pallidal-subthalamo-nigral) dominate during goal-driven behavior with instructed rewards, while facilitatory pathways (striato-nigral and subthalamo-pallidal-nigral) dominate during unconstrained (free reward) conditions.
Highlights
By classifying stimulation effects broadly into ‘Inh’ and ‘Fac’ categories to generalize the STN and SNr results described in detail above, the opposite effects of STN and SNr stimulation during free viewing (Fig. 5d, e, blue bars) but comparable effects during goal-driven anti-saccades (Fig. 5d, e, red bars) are clearly observable, supporting explicit task-dependent changes within the BG
We limited our discussion to the goal-directed antisaccade condition as this was the best suited for comparison to free viewing saccades
The pro-saccade results were qualitatively similar to the anti-saccade results, but with a smaller absolute magnitude of effect
Summary
We aimed to determine whether the tonic weighting between inhibitory and excitatory pathways from the STN (BG input and relay structure) to the substantia nigra pars reticulata (SNr; BG output structure) may alter according to behavioral context (Fig. 1c)
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