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

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.

Brain activation of eye movements in subjects with refractive error.

PURPOSE: Recent functional magnetic resonance imaging (fMRI) studies have described reorganized activation of the oculomotor and visual cortex after focal brain lesions. These studies are based on comparison with healthy individuals who may have a very heterogenous refractive error. The influence of refractive error on the cortical control of an oculomotor task such as a prosaccade trial, however, is unknown. METHODS: To investigate the influence of visual acuity on changes of cortical oculomotor control, we studied the representation of visually guided prosaccades in nine subjects with refractive error and 11 normally sighted subjects using fMRI. Correction of refractive error was not allowed during fMRI. Differences in activation between rest and saccades as well as between subjects with refractive error vs subjects with normal vision were assessed with statistical parametric mapping. RESULTS: In both groups, activation of a frontoparietal network was observed. Subjects with refractive errors showed increased activation compared to normally sighted subjects, with overactivation in bilateral frontal and parietal eye fields, supplementary eye fields, as well as in the bilateral extrastriate cortex. CONCLUSIONS: This group of subjects with refractive error showed increased activation in an extended oculomotor and visual network to maintain performance during simple prosaccades. This observation underlines the importance of using appropriate control groups in fMRI-studies after brain lesions.

Age-related differences of saccade induced cortical activation.

Recent functional MRI (fMRI) studies have described the increased task-related brain activation in older subjects during motor, cognitive and perceptual tasks. Age affects the ability to control saccadic eye movements. To investigate the age-related changes of oculomotor control, we studied the representation of saccades in 11 young (median age 29 years) and 11 older (median age 62 years) healthy individuals using fMRI. Brain activation was measured during a visually guided prosaccade trial. Differences in activation between rest and saccades as well as between younger and older subjects were assessed with statistical parametric mapping (SPM). In both age groups, activation of a frontoparietal network was observed. Older subjects showed increased activation compared to younger subjects with overactivation in bilateral parietal eye fields, the right frontal eye field, as well as in the right extrastriate cortex. We conclude that older adults increase activation in an extended oculomotor and visual network to maintain performance during simple prosaccades. This observation also underlines the importance of using appropriate age-matched control groups in fMRI studies after brain lesions.

Eye-movement training-induced plasticity in patients with post-stroke hemianopia.

Substantial disability in patients with hemianopia results from reduced visual perception. Previous studies have shown that these patients have impaired saccades. Improving exploratory eye movements with appropriate training of saccades may help to partially compensate for the visuoperceptive impairment during daily life activities. The changes in cortical control of eye movements that may be induced by these training strategies, however, are not known. We used functional magnetic resonance imaging (fMRI) to study the training effects of eye-movement training on cortical control of saccades. Brain activation during visually guided saccades was measured in eight patients with an occipital cortical lesion causing homonymous hemianopia. Starting 8 weeks after the stroke, patients received 4 weeks of visual field training. The 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 saccades as well as before and after training were assessed with statistical parametric mapping software (SPM'99). Twelve healthy subjects were scanned twice at a 4-week interval. In patients, significant activation at baseline was found in the frontal and parietal eye fields (FEF and PEF, respectively) bilaterally and in the supplementary eye field (SEF). Immediately after training, an area of increased activation was found in the left extrastriate cortex of the affected hemisphere. At follow-up, relatively more activation was found in the right peristriate cortex and in the SEF of the unaffected side. A relative decrease of activation was found in the left FEF. In this group of patients, eye-movement training induced altered brain activation in the striate and extrastriate cortex as well as in oculomotor areas.

Cortical activation in hemianopia after stroke.

Changes in neuronal activity of the visual cortex have been described in patients with hemianopia. The anatomical areas that are involved in neuroplastic changes have not been studied in a larger group of stroke patients with a homogenous structural pathology of the visual cortex. Brain activation was measured in 13 patients with a single ischemic lesion of the striate cortex and partially recovered hemianopia and in 13 age-matched control subjects using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI). Differences in activation between rest and visual hemifield stimulation were assessed with statistical parametric mapping using group and multi-group studies. In normal subjects, the most significant activation was found in the contralateral primary visual cortex (area 17) and bilaterally in the extrastriate cortex (areas 18 and 19). In patients, these areas were also activated when the intact hemifield was stimulated. During stimulation of the hemianopic side, bilateral activation was seen within the extrastriate cortex, stronger in the ipsilateral (contralesional) hemisphere. Stimulation of the hemianopic visual field is associated with ipsilateral activation of the extrastriate visual cortex. This pattern of activation suggests extensive neuronal plasticity within the visual cortex after postgeniculate ischemic lesions and may have implications for therapeutic interventions.

Saccade induced cortical activation in patients with post-stroke visual field defects.

Substantial disability in patients with hemianopia results from reduced visual perception. Several studies have shown that these patients have impaired saccades but may improve search strategies with appropriate training of saccades. We used fMRI to study the representation of saccades in patients with post-stroke hemianopia to the left. Brain activation during visually guided saccades was measured in 10 patients with a pure occipital cortical lesion causing homonymous hemianopia and in 10 healthy control subjects. Differences in activation between rest and saccades and between controls and patients were assessed with statistical parametric mapping (SPM'99). In normal subjects, significant activation was found in the frontal and parietal eye fields bilaterally and in the supplementary eye field. These areas were also activated in patients, however, to a lesser degree. In contrast, an area of increased activation in patients was found in the posterior parietal cortex of the (non-affected) left hemisphere. Visual field defects after striate lesions are associated with changes in the frontoparietal network underlying the cortical control of saccades.