Proprioceptive contribution to oculomotor control in humans.

Area of Science:

• Neuroscience
• Ophthalmology
• Human Physiology

Background:

• Proprioceptive feedback is crucial for fine motor control, but its role in eye movement control is not fully understood.
• Humans have numerous muscle spindles in extraocular muscles (EOMs), unlike macaques, suggesting a potential role for proprioception in human eye movements.
• Previous human behavioral studies suggest EOM proprioception's involvement, contrasting with macaque studies.

Purpose of the Study:

• To investigate whether human oculomotor nuclei respond to proprioceptive feedback from EOMs.
• To determine if proprioceptive stimulation of one EOM can influence the movement of the contralateral eye.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to observe brain activity in oculomotor nuclei during a proprioceptive task.
• Participants gently pushed their eyeball to stretch EOMs while in a controlled environment.
• Eye-tracking experiments in darkness were conducted to measure eye movements in response to EOM proprioceptive stimulation.

Main Results:

• fMRI showed activation in the left oculomotor nucleus and subthreshold activation in the left abducens nucleus when the right lateral rectus muscle was stretched.
• Eye-tracking confirmed that the left eye moved actively in the direction of the passive displacement of the right eye.
• The contralateral eye movement occurred with a smaller amplitude than the passive displacement.

Conclusions:

• The human oculomotor system responds to proprioceptive feedback from EOMs.
• Proprioceptive input from one eye's muscles can trigger compensatory movements in the other eye, contributing to ocular alignment.
• These findings highlight a significant role for proprioception in maintaining binocular vision and eye coordination.