Eye-movement training-induced changes of visual field representation in patients with post-stroke hemianopia

Abstract

Changes in neuronal activity have been described in patients with hemianopia following ischemic lesions of the visual cortex. This reorganization may facilitate compensation of lost visual function that is rarely fully restituted. Improving exploratory eye movements with appropriate training has been shown to partially compensate for the visuoperceptive impairment during daily life activities. The changes in cortical processing of visual stimuli that may be induced by these training strategies, however, are less well described. We used fMRI to study the training effects of eye-movement training on cortical representation of visual hemifields. Brain activation during hemifield stimulation was measured in eight patients with an occipital cortical lesion of the striate cortex causing homonymous hemianopia. Starting 8 weeks after the stroke, patients received 4 weeks of eye movement training. fMRI measurements were performed at baseline and after training. In five patients, follow-up fMRI was performed 4 weeks after the end of training. Differences in activation between rest and hemifield stimulation as well as before and after training were assessed with statistical parametric mapping. Twelve healthy subjects were scanned twice at a 4-week interval. During stimulation of the affected hemifield, significant activation at baseline was found bilaterally in extrastriate cortical areas, with the strongest increases in the contralesional hemisphere. This activation pattern was maintained after training. Four weeks after the end of training, there was an additional activation of the extrastriate cortex in the contralesional hemisphere compared to baseline. No changes in the size of visual field defects were found. In this group of patients, eye-movement training induced altered brain activation in the unaffected extrastriate cortex.