Two-dimensional saccade-related population activity in superior colliculus in monkey

Area of Science:

• Neuroscience
• Ophthalmology
• Systems Neuroscience

Background:

• The superior colliculus (SC) plays a crucial role in controlling saccadic eye movements.
• Previous research suggested a rostral spread of activity in the SC during saccades, but lacked detailed two-dimensional mapping.

Purpose of the Study:

• To estimate the two-dimensional population activity distribution in the monkey superior colliculus (SC) during saccadic eye movements.
• To investigate the spatial dynamics of neural activity in different SC layers (burst and buildup) relative to saccade parameters.

Main Methods:

• Recorded neural activity from deeper SC layers across a wide rostrocaudal and mediolateral extent in monkeys.
• Utilized radial basis functions to estimate two-dimensional population activity at 2-ms intervals around saccades.
• Differentiated cell layers (dorsal/burst and ventral/buildup) based on depth and presaccadic activity patterns.

Main Results:

• Burst layer activity was invariant and symmetrically arranged around a stable center of gravity.
• Buildup layer activity size increased with saccade amplitude, showing a rostral skew for larger saccades (>10 degrees).
• A small, consistent shift in the center of gravity was observed along movement meridians, but spread was not solely rostral.

Conclusions:

• SC activity changes occur in an extended zone, not a simple rostral spread, during saccades.
• Findings do not support a rostrally directed spread of activity as the primary dynamic control mechanism for saccades.
• Two-dimensional mapping provides a more comprehensive understanding of SC population dynamics during eye movements.