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Andre Gouws, Holly Brown, Rachel Woodall, Antony Morland; Assessing the functional properties of primary visual cortex in the absence of extrastriate visual areas.. Journal of Vision 2018;18(10):28. doi: https://doi.org/10.1167/18.10.28.
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© ARVO (1962-2015); The Authors (2016-present)
Patient H was introduced to us several years after a stroke that resulted in an extensive unilateral lesion affecting her left occipital cortex and underlying white matter. She has a corresponding homonymous right visual field defect. Intriguingly, close inspection of MRI data of the occipital lobe suggested that cortical tissue is preserved within the calcarine sulcus in the damaged hemisphere, usually the location of V1. Little or no spared tissue is seen in locations that would usually represent visual areas V2, V3 and likely other extrastriate visual areas. As there is little evidence of atrophy of the cortex along in the calcarine sulcus, we sought to characterise the structural integrity of the projection from the LGN to it to establish whether there was a potential input to V1 that escaped the lesion. Tractography of diffusion-weighted imaging at 3T revealed an intact projection from the LGN to the spared calcarine tissue, and tract characteristics were comparable with those in H's healthy, right hemisphere. Next, we tested whether any residual activity to visual stimulation might be detected in spite of the dense visual field defect. A block-design, alternating left-vs-right visual field, fMRI experiment revealed robust BOLD responses in the spared calcarine tissue in both hemishperes to stimuli presented in the contralateral hemifield. Furthermore, standard fMRI retinotopic mapping paradigms revealed that functional responses remain organised in a manner consistent with an intact retinotopic map. Our results indicate that even after a considerable period of time since the lesion, an 'isolated' V1 registers its thalamic inputs, which remain organized retinotopically. It is interesting to note that the activity in V1 alone does not appear to underpin behavioural responses to stimuli.
Meeting abstract presented at VSS 2018
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