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Jody C. Culham, Jessica K. Witt, Kenneth F. Valyear, Gordon N. Dutton, Melvyn A. Goodale; Preserved processing of motion and dorsal stream functions in a patient with large bilateral lesions of occipitotemporal cortex. Journal of Vision 2008;8(6):372. doi: 10.1167/8.6.372.
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© ARVO (1962-2015); The Authors (2016-present)
We used anatomical and functional magnetic resonance imaging (fMRI) at 4 Tesla to examine the damaged and spared brain regions in Patient MC, a 38-year old woman with Riddoch phenomenon - awareness of moving but not static stimuli. Anatomical scans indicated extensive damage to occipitotemporal cortex bilaterally and right posterior parietal cortex. Within occipital cortex, the only spared and visually active region was a small portion of the anterior calcarine cortex bilaterally. The expected location of the lateral occipital complex in neurologically intact subjects fell within the lesion, consistent with MC's absence of object-selective activation for both static and moving stimuli. Similarly, no face-, place- or body-selective activation for static or moving stimuli was observed. In contrast to the severe damage to early visual areas and ventral stream areas, numerous areas within the dorsal stream remained intact and functional. Consistent with MC's awareness of motion, fMRI revealed motion-selective activation bilaterally in the MT+ complex, just ahead of the occipitotemporal damage. Consistent with the preserved accuracy of her hand actions, MC showed robust grasp-selective activation in the anterior intraparietal area bilaterally and reach-selective activation in the superior parieto-occipital cortex of the left hemipshere. When shown movie clips of hands acting with tools, activation was observed in areas implicated in tool processing (intraparietal sulcus/supramarginal gyrus, middle temporal gyrus) and action observation (superior temporal sulcus). These results suggest that MC's dorsal stream continues to receive input either from a very limited extent of visual cortex or, more likely, from extrageniculostriate projections, two possibilities currently under investigation with diffusion tensor imaging. In sum, the damaged and activated regions within MC's brain are highly consistent with her behavioral deficits (Goodale et al., VSS 2008) in ventral stream functions (recognition) and her preserved abilities for several dorsal stream functions (motion perception, reaching, grasping, and tool observation).
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