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K. L. Main, K. P. Moloney, E. N. Kinzel, J. Ginn, T. A. Adelore, S. A. Primo, J. A. Jacko, E. H. Schumacher; Plasticity From Macular Degeneration Results in Changes in Extrastriate Visual Cortex. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3304. doi: https://doi.org/.
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The progression of macular degeneration (MD) results in the disconnection of optic fibers stemming from certain parts of the retina (macula) to initial areas of visual processing (V1) in the occipital lobe. Recent research suggests that such a change in input may cause a topographic reorganization of the retina’s representation on the calcarine sulcus (Baker et al., 2005). This entails disconnected cortex responding to visual stimuli outside of its normal receptive field (i.e. stimuli presented to the peripheral retina). Though evidence is mounting that reorganization due to MD affects the striate cortex or V1, little is known about the extent of this reorganization in down-stream extrastriate brain areas. For example, feed forward connections from V1 could initiate reorganization in a number of higher level visual processors dealing with spatial attention. To investigate this possibility we performed both behavioral and fMRI experiments on participants with MD and age-matched controls.
Use of MP-1 microperimetry (Nidek, Inc) ensured an accurate assessment of retinal health and eccentric viewing. Attention and visual performance was evaluated behaviorally with computer-based testing and neurologically with a 3T magnet.
We found marked behavioral differences in how attention is allocated by MD participants compared to visually healthy controls. Attention is more easily allocated to areas of preferred eccentric viewing in MD patients. These differences were supplemented with data from brain activation experiments showing that MD patients lacked the normal contralateral activity patterns exhibited by controls in a bilateral attention task.
Our findings indicate the possibility of substantial plastic changes in those with MD apart from reorganization of V1. Understanding the behavioral and neurological impact of such plasticity on human visual perception and performance could lead to visual therapies and interventions for those with MD.
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