Injury to the primary visual cortex (V1) typically leads to loss of conscious vision in the corresponding, homonymous region of the contralateral visual hemifield (scotoma). Several studies suggest that V1 is highly plastic after injury to the visual pathways, whereas others have called this conclusion into question. We used functional magnetic resonance imaging (fMRI) to measure area V1 population receptive field (pRF) properties in five patients with partial or complete quadrantic visual field loss as a result of partial V1+ or optic radiation lesions. Comparisons were made with healthy controls deprived of visual stimulation in one quadrant ["artificial scotoma" (AS)]. We observed no large-scale changes in spared-V1 topography as the V1/V2 border remained stable, and pRF eccentricity versus cortical-distance plots were similar to those of controls. Interestingly, three observations suggest limited reorganization: (i) the distribution of pRF centers in spared-V1 was shifted slightly toward the scotoma border in 2 of 5 patients compared with AS controls; (ii) pRF size in spared-V1 was slightly increased in patients near the scotoma border; and (iii) pRF size in the contralesional hemisphere was slightly increased compared with AS controls. Importantly, pRF measurements yield information about the functional properties of spared-V1 cortex not provided by standard perimetry mapping. In three patients, spared-V1 pRF maps overlapped significantly with dense regions of the perimetric scotoma, suggesting that pRF analysis may help identify visual field locations amenable to rehabilitation. Conversely, in the remaining two patients, spared-V1 pRF maps failed to cover sighted locations in the perimetric map, indicating the existence of V1-bypassing pathways able to mediate useful vision.cortical blindness | quadrantanopia | plasticity | retinotopy | hemianopia C ortical damage of the visual pathway often results from posterior or middle cerebral artery infarcts, hemorrhages, and other brain injuries. The most common visual cortex lesions involve the primary visual cortex (V1), the chief relayer of visual information to higher visual areas. Damage to area V1 or its primary inputs leads to the loss of conscious vision in the corresponding region of the contralateral visual hemifield, producing a dense contralateral scotoma that often covers a hemifield (hemianopia) or a single visual field quadrant (quadrantanopia).A much-debated issue is whether the adult V1 is able to reorganize after injury. Reorganization refers to long-term changes in the neuronal circuit (1) and generally requires the growth of new anatomic connections or a permanent change in the strength of existing connections. Several studies report significant remapping in area V1 of patients suffering from macular degeneration and other retinal lesions (2-12). The extent of this remapping has recently been called into question, however (1,(13)(14)(15)(16)(17)(18)(19). Less is known about how the visual system remaps to cover the visual field after injury to a...
The noninvasive estimation of neuronal receptive field (RF) properties in vivo allows a detailed understanding of brain organization as well as its plasticity by longitudinal following of potential changes. Visual RFs measured invasively by electrophysiology in animal models have traditionally provided a great extent of our current knowledge about the visual brain and its disorders. Voxel-based estimates of population RF (pRF) by functional magnetic resonance imaging (fMRI) in humans revolutionized the field and have been used extensively in numerous studies. However, current methods cannot estimate single-neuron RF sizes as they reflect large populations of neurons with individual RF scatter. Here, we introduce an approach to estimate RF size using spatial frequency selectivity to checkerboard patterns. This method allowed us to obtain noninvasive, average single-neuron RF estimates over a large portion of human early visual cortex. These estimates were significantly smaller compared with prior pRF methods. Furthermore, fMRI and electrophysiology experiments in nonhuman primates demonstrated an exceptionally good match, validating the approach.
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