A competition framework for fixation-preference in strabismus

Area of Science:

• Neuroscience
• Ophthalmology
• Computational Neuroscience

Background:

• Strabismus, or eye misalignment, often leads to a fixation preference, where individuals consistently use one eye over the other.
• Fixation preference in strabismus is known to vary with target location, suggesting complex oculomotor control mechanisms.
• Existing models propose that the brain must choose between competing retinal errors to direct eye movements in strabismic individuals.

Purpose of the Study:

• To investigate the neural basis of fixation preference in strabismus using a competitive decision framework.
• To examine the role of the superior colliculus (SC) in processing competing visual signals for eye-choice.
• To determine if a competition framework can explain oculomotor fixation preference in strabismus.

Main Methods:

• Recorded visuo-motor neuron activity in the superior colliculus (SC) of two strabismic rhesus macaque monkeys.
• Monkeys performed a delayed saccade task under binocular viewing conditions with eccentric targets.
• Manipulated target locations to correspond with receptive fields of either the viewing or deviated eye.

Main Results:

• Observed robust visual sensory responses to targets at both viewing and deviated eye receptive field locations, indicating competing signals.
• Found greater visual and build-up activity in SC neurons when the saccade encoded by the neuron 'won' at fixation-switching locations.
• Demonstrated evidence of visual suppression within SC sensory activity.

Conclusions:

• Findings support a competition framework for explaining fixation-preference behavior in strabismus.
• The superior colliculus (SC) plays a role in processing competing sensory information to drive eye-choice.
• This competition framework may be a general mechanism for target selection in both aligned and misaligned vision.