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Jodie Davies-Thompson, Linda J. Lanyon, Jason J.S. Barton; Functional organisation of visual pathways in a patient with no optic chiasm. Journal of Vision 2012;12(9):787. doi: https://doi.org/10.1167/12.9.787.
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Background: Patients with albinism or congenital achiasma offer a unique opportunity to study cerebral reorganization and inter-hemispheric communication in the face of highly anomalous inputs to striate cortex.
Objective: We describe neuroimaging studies in a patient with congenital achiasma and seesaw nystagmus, but full visual fields.
Methods: The subject underwent structural MRI, DTI studies, and functional MRI with monocular stimulation with light/dark checkerboards, motion, and objects and faces, as well as retinotopic quadrantic stimulation.
Results: Structural MRI confirmed the absence of an optic chiasm, which was corroborated by diffusion tensor imaging (DTI). Monocular full-field presentation of chequerboards resulted in activation restricted to the ipsilateral primary visual cortex, providing functional confirmation of a lack of crossing visual inputs to striate cortex. Areas V2 and V3 also showed activation only by the ipsilateral eye. Additional analysis showed no difference between the on and off conditions in the contralateral visual cortex, indicating no sub-threshold activation in V1-V3 and confirming a true lack of response to visual stimulation. Monocular retinotopic stimulation of the left and right visual fields further showed reorganisation within primary visual cortex. Monocular presentation of motion versus static stimuli revealed bilateral activation in the area V5 complex by stimuli presented to either eye, Similarly monocular presentation of faces and objects produced bilateral activation in the posterior and middle fusiform gyrus.
Conclusions: These results show the functional reorganisation of striate cortex to anomalous monocular full-field input and indicate that inter-hemispheric integration of information does not occur at early V2/V3 levels, but at an intermediate stage (V5) and higher levels (fusiform gyri).
Meeting abstract presented at VSS 2012
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