Dissociation of Object and Spatial Vision in Human Extrastriate Cortex: Age-Related Changes in Activation of Regional Cerebral Blood Flow Measured with [15 O]Water and Positron Emission Tomography

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Abstract
We previously reported selective activation of regional cerebral blood flow (rCBF) in occipitotemporal cortex during a face matching task (object vision) and activation in superior parietal cortex during a dot-location matching task (spatial vision) in young subjects, The purpose of the present study was to determine the effects of aging on these extrastriate visual processing systems. Eleven young (mean age 27 ± 4 years) and nine old (mean age 72 ± 7 years) male subjects were studied. Positron emission tomographic scans were performed using a Scanditronix PC1024–7B tomograph and H2 15O to measure rCBF. To locate brain areas that were activated by the visual tasks, pixel-by-pixel difference images were computed between images from a control task and images from the face and dot-location matching tasks. Both young and old subjects showed rCBF activation during face matching primarily in occipitotemporal cortex, and activation of superior parietal cortex during dot-location matching. Statistical comparisons of these activations showed that the old subjects had more activation of occipitotemporal cortex during the spatial task and more activation of superior parietal cortex during the object task than did the young subjects. These results show less functional separation of the dorsal and ventral visual pathways in older subjects, and may reflect an age-related reduction in the processing efficiency of these visual cortical areas.