Activation of human extrageniculostriate pathways after damage to area V1

We have used positron emission tomography (PET) to specify the cortical and subcortical structures activated following visual stimulation of the scoto matous held in a patient with an asymmetric bilateral developmental anomaly of the visual cortex. Computerized perimetry indicated a left visual held defect only although MRI and (18)FDG-PET scans showed abnormalities in both occipital lobes. The visual stimuli were semicircular gratings moving in o pposite directions on a dynamic random-dot background. They were specifical ly constructed to eliminate intra- and extraocular light scatter and to opt imize the activation of extra-striate cortical areas and their projecting s ubcortical relays. For anatomical localization PET images were coregistered to the subject's MRI in Talairach coordinates. After subtraction of the ba seline conditions from the stimulation conditions, a t-statistic map was cr eated on a voxel-by-voxel basis. Stimulation of the scotomatous hemifield y ielded significant activations of Brodmann cortical areas 18-19 and 47 as w ell as the pulvinar thalami of the left hemisphere, in addition to a less p rominent activation in the right hemisphere. Stimulation of the intact hemi field produced significant activation of Brodmann cortical areas 30 and 47 of the left hemisphere. These results suggest that in the absence of area V 1, residual vision observed in the blind hemifield could be mediated by a r etinofugal pathway to extrastriate cortex via the pulvinar. (C) 1999 Academ ic Press.