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Abnormal spatial localization with trigeminal-oculomotor synkinesis. Evidence for a proprioceptive effect
1Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Brain : a Journal of Neurology
|October 1, 1993
Summary
This study on trigeminal-oculomotor synkinesis reveals that proprioceptive signals from eye muscles, not efference copy, guide spatial localization. Abnormal muscle activation in synkinesis provides unique insights into eye position sensing.
Area of Science:
- Neuroscience
- Ophthalmology
- Sensory Neuroscience
Background:
- Investigating spatial localization mechanisms is crucial for understanding sensorimotor control.
- Congenital trigeminal-oculomotor synkinesis offers a unique model to dissociate efference copy from proprioceptive feedback in eye movements.
Observation:
- A patient with trigeminal-oculomotor synkinesis exhibited abnormal left medial rectus co-activation during left lateral pterygoid contraction.
- During monocular viewing, aberrant synkinetic adduction of the covered left eye caused the patient to point left of the visual target.
Findings:
- Proprioceptive afference from the extraocular muscles, not central efference copy, was utilized for spatial localization.
- Active synkinetic eye adduction shifted pointing direction opposite to the non-viewing eye's rotation, unlike passive movements in normal subjects.
Implications:
- This suggests that proprioceptive information from extraocular muscles plays a primary role in eye position sense.
- The findings challenge previous assumptions and highlight the distinct roles of tendon organs versus muscle spindles in proprioception.