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Abstract:
Damage to the primary visual cortex (V1) as a result of stroke or other brain diseases can lead to a loss of conscious vision in the contralateral visual hemifield. Cortical blindness affects many activities on a patient's daily life and is considered to be a heavy burden while there are few, if any, options for rehabilitation and recovery. A much debated issue is whether the visual cortex is able to reorganize after injury in adult human subjects, and if so, what may be the mechanism of reorganization. Here we apply an important new approach introduced by Dumoulin and Wandell (Doumoulin 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. The purpose of this study is to compare receptive field measurements in patients with cortical lesions with controls and to investigate whether these measurements change following injury. Patients were fixating in the magnet and fMRI measurements were obtained during the presentation of standard visual stimuli used in retinotopic mapping (rotating wedges, expanding rings, horizontally and vertically moving bars). The patient’s intact hemisphere, as well as normal subjects were used as controls. In some controls an area of the stimulus was obscured (“artificial scotoma”) to simulate as much as possible the real scotoma of the patients. Preliminary results suggest that receptive field measurements obtained in patients and in subjects examined under the artificial scotoma condition differ from measurements obtained in controls under the normal visual stimulation condition. We are in the process of obtaining further control tests and measurements to confirm these findings and to assess to what degree they correspond to cortical reorganization. Future research will focus on using these methods to study the capacity of various visual rehabilitation training methods to induce visual cortex reorganization.
