Volitional control of homonymous hemianopsia: a single case study.

A 52-year-old woman suffered a posterior left hemisphere infarction involving the geniculo-striate system with right homonymous hemianopsia. Eighteen months after the stroke, we used perimetry and PET imaging of cerebral blood flow to demonstrate the patient's volitional control over the size of the scotoma. The volitional control could be eliminated with competing cognitive tasks. Significant increases in cerebral blood flow in contralateral medial prefrontal cortex, and in ipsilateral dorsolateral frontal convexity, temporoparietal and insular cortex were associated with volitional control of the visual field defect.