Substantia nigra stimulation influences monkey superior colliculus neuronal activity bilaterally

Area of Science:

• Neuroscience
• Motor Control
• Basal Ganglia Function

Background:

• The basal ganglia's inhibitory output is crucial for controlling orienting movements.
• The substantia nigra pars reticulata (SNr) projects to the superior colliculus (SC) to mediate this inhibition.
• The influence of SNr on SC buildup neurons and the contralateral SNr-SC pathway in alert monkeys remain under-explored.

Purpose of the Study:

• To investigate the effect of SNr stimulation on SC buildup neurons in alert monkeys.
• To explore the role of the SNr-SC pathway in modulating saccadic eye movements.

Main Methods:

• Electrical stimulation of the SNr (one or both nuclei) in alert monkeys.
• Recording neuronal activity from SC buildup neurons during stimulation.

Main Results:

• SNr stimulation bilaterally reduced the discharge rate of SC buildup neurons, indicating an inhibitory drive.
• The inhibitory influence from the ipsilateral SNr lasted longer (approx. 73 ms) than from the contralateral SNr (approx. 34 ms).
• SNr stimulation altered the variability of saccade onset time and direction.

Conclusions:

• SNr inhibitory output modulates SC buildup neuron activity in both hemispheres.
• SNr inhibition plays a subtle role in visually guided saccades, influencing the excitation-inhibition balance rather than acting as a simple gate.