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Zusammenfassung:
Damage to the primary visual cortex (V1) as a result of stroke typically leads to the inability to perceive visual stimuli in the affected region of the contralateral visual hemifield (scotoma). However, in spite of this, several higher visual areas have been shown to be modulated by visual stimuli presented inside the scotoma. A much debated issue is whether adult visual cortex is able to reorganize after injury, and if so, what is the extent and the mechanism of the observed reorganization. Here we use functional magnetic resonance imaging (fMRI) methods to study visual cortex reorganization after injury in adult human subjects. To this end we applied a method introduced by Dumoulin and Wandell (Dumoulin SO, Wandell BA, Population receptive field estimates in human visual cortex, Neuroimage 39, 2008), which uses functional magnetic resonance imaging (fMRI) to measure the aggregate receptive field properties of neuronal populations voxel by voxel in the visual cortex. FMRI measurements were obtained during the presentation of a moving bar stimulus which traversed the visual field while the subjects were fixating and these measurements were used to derive an estimate of the voxel based population receptive field centre and radius. We studied several subjects with quadrandanopsia and hemianopsia resulting from cortical lesions and compared them to the range of measurements obtained from a group of normal controls. In general, retinotopic maps in the patients’ spared early visual cortex appear to be consistent with retinotopic maps obtained in control subjects. The organization of higher level visual areas, such as V3a/b and MT show preliminary some differences compared to those of normal subjects. Also preliminary results on the population receptive field size of some of the patients’ spared visual areas show deviations from the normal range of population receptive field sizes derived from the control subjects. We are in the process of obtaining further measurements to confirm these findings and to assess to what degree they correspond to cortical reorganization.
