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Ehud Zohary, Danny Dilks, Nancy Kanwisher, Alvaro Pascual-Leone; Does cortical reorganization lead to a corresponding change in readout?. Journal of Vision 2008;8(6):492. doi: 10.1167/8.6.492.
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© ARVO (1962-2015); The Authors (2016-present)
Recent studies have demonstrated reorganization of retinotopic cortex in some individuals with macular degeneration (MD): stimuli presented to the subjects' visual periphery activate cortical regions that are normally responsive only to stimuli presented at the fovea (Baker et al., 2005). Here we asked whether this cortical reorganization leads to a corresponding change in the interpretation, or “readout” of the activation in the altered part of the cortical map. That is, when normally-foveal cortex is activated, do subjects with an altered cortical map perceive the stimulus to be at the fovea (according to the original “meaning” of this activation), or at the periphery (in the location that now drives this part of cortex)? The latter result would imply that the interpretation of information from reorganized cortex has changed accordingly; the former result would imply it has not changed. To answer this question we compared the effects of transcranial magnetic stimulation (TMS) to the occipital pole in control subjects and two individuals with MD who showed massive reorganization of the normally-foveal cortex as revealed by fMRI (see Baker et al. 2005). TMS elicited a sensation of faint light (phosphenes) in the central visual field in all (n=10) control subjects. TMS led to distinctly different outcomes in the two MD subjects. One MD subject systematically reported the phosphenes near the center of gaze, in locations where he had no visual experience for years. The other MD subject consistently reported phosphenes in the visual periphery, about ∼20deg from the fovea where none of the control subjects ever reported a phosphene. Thus, the second subject showed a change in the readout of his reorganized cortical map, but the first subject did not. Future work will attempt to identify the critical factors that determine if a change in readout will occur following cortical reorganization.
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