Abnormal cortical activation in response to motion in people who have lost one eye early in life

Abstract

Early monocular visual deprivation such as amblyopia is associated with deficits in the perception of motion as well as spatial vision and a decrease in cortical activation in response to motion (Bonhomme et al., 2006). Early unilateral enucleation (removal of an eye), however, results in deficits in the perception of motion but not spatial vision. This latter patient group provides a valuable model to examine the effects of a loss of binocularity on visual motion processing without the potential confound of poor spatial visual ability. We compared cortical activation for motion in early enucleated patients compared to controls using fMRI. Participants: To date, we have tested two adult patients with unilateral eye enucleation before the age of two years and three binocularly intact controls viewing monocularly and binocularly. Methods: Stimuli consisted of white random dot patterns on a black background within a circular aperture. Using a block design motion localizer, stimuli alternated in time between 16 seconds of motion (linear motion in eight different directions, changing direction every second) and 16 seconds of stationary dots. Results: Talairach coordinates for area MT in the one eyed patients are consistent with those of the controls. Preliminary results indicate a greater extent of activation in response to motion in the patients compared to controls in area MT ipsilateral to the remaining eye. The patient with the earliest age at enucleation also shows morphological differences such that early visual areas in the hemisphere ipsilateral to the remaining eye are larger compared to the opposite hemisphere. Conclusions: Unlike deprivation from amblyopia and despite previous behavioural findings for deficits in motion perception with early enucleation, our patients show more activation in response to motion. These findings suggest that early unilateral enucleation results in unique cortical reorganization at both an anatomical and functional level.

Footnotes

 Supported by a grant from The Banting Research Foundation.