Bilateral functional MRI activation of the basal ganglia and middle temporal/medial superior temporal motion-sensitive areas - Optokinetic stimulation in homonymous hemianopia

Objective: To determine to what extent sensorimotor control is achieved for each hemisphere separately or interactively during small-field optokinetic stimulation in patients with complete homonymous hemianopia. Design: Functional and structural neuroimaging using high-resolution magnetic resonance imaging. Setting: University medical center research facility. Patients: Three patients with complete homonymous hemianopia after acute infarction of the right posterior cerebral artery. Main Outcome Measures: Anatomical location of activated structures during horizontal optokinetic stimulation and T-2-weighted anatomical magnetic resonance imaging. Results: Occipitotemporal cortical areas (Brodmann areas 39 and 40) were the only activated cortical structures that showed statistically significant (P < .01) activation on the affected hemisphere. Of the subcortical areas, activation of thalamic nuclei appeared to be missing on the affected side, whereas the basal ganglia (putamen, globus pallidus, and caudate nucleus) were bilaterally activated. Conclusions: Bilateral activation of the basal ganglia confirms the concept of the basal ganglia-thalamocortical motor loop and of the efference copy of oculomotor pathways from each hemisphere. Our findings suggest 2 possible explanations for the activation of occipitotemporal areas (the human homolog of middle temporal/medial superior temporal areas) on the infarcted hemisphere: involvement of direct extrastriatal visual pathways or interhemispheric callosal connections between right and left middle temporal/medial superior temporal areas.