Collicular microstimulation during passive rotation does not generate fixed gaze shifts.

Area of Science:

• Neuroscience
• Oculomotor control
• Vestibular system

Background:

• The superior colliculus plays a critical role in generating saccadic eye movements.
• Vestibular input influences eye movements to maintain gaze stability during head motion.
• Understanding the interaction between saccades and vestibular signals is crucial for explaining gaze control.

Purpose of the Study:

• To investigate if electrically evoked saccades (E-saccades) from the superior colliculus can compensate for passive head rotation.
• To analyze the metric and kinematic effects of head rotation on E-saccades.
• To determine the directionality and magnitude of gaze-shift constancy violations.

Main Methods:

• Electrical stimulation of the superior colliculus in monkeys to evoke saccades (E-saccades).
• Passive sinusoidal head rotation in yaw and pitch.
• Analysis of horizontal and vertical components of E-saccades, including onset position, metric changes, and peak velocity.
• Comparison of compensatory and anticompensatory effects relative to head velocity and rotation direction.

Main Results:

• Significant horizontal metric changes in E-saccades were observed, proportional to head velocity.
• Compensatory adjustments were often insufficient, and anticompensatory changes were common, violating gaze-shift constancy.
• A robust kinematic effect showed increased horizontal peak velocity with rotation in the E-saccade direction.
• Both metric and kinematic effects aligned with the direction of head rotation.

Conclusions:

• Electrically evoked saccades interacting with head rotation do not consistently maintain gaze-shift constancy.
• Vestibular-saccade interactions, both metric and kinematic, can be compensatory or anticompensatory.
• The findings suggest convergence of saccadic and vestibular signals at a downstream component-coding stage.