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Abstract

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. 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 center 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.