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Michèle MacLean, Vanessa Hadid, Latifa Lazzouni, Franco Lepore; Using fMRI to Identify Neuronal Mechanisms of Motion Detection Underlying Blindsight. Journal of Vision 2018;18(10):768. doi: 10.1167/18.10.768.
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Research on the visually impaired offers a valuable model of functional brain plasticity by showing how sensory inputs reshape cortical activations. Following a unilateral post-chiasmatic lesion affecting the visual cortex, patients suffer a controlateral visual loss referred to as Homonymous Hemianopia. Nevertheless, these patients preserve the ability to unconsciously detect, localize and discriminate visual stimuli presented in their impaired visual field. To investigate this paradox, known as blindsight, we have conducted a study using brain imaging techniques to evaluate the structural and functional impact of such lesion in Homonymous Hemianopia patients. In doing so, we collected whole brain and sliced thalamic fMRI scan sequences during resting state and a motion detection task. Subjects with a right or left hemianopia underwent a series of visual tasks to correlate blindsight performances with neural activity. Accurate performance demonstrates their ability to unconsciously perceive motion presented in the blind hemifield and the presence of residual vision. When compared to neurotypical matched controls, we observed strong anatomical and functional differences as well as asymmetrical BOLD activations. As the main visual pathways were lesioned, these findings suggest that (1) sub-cortical pathways, including the superior colliculus projections to the middle temporal area as well as the new formed pathways absent in normal vision, are responsible for processing and relaying visual information; (2) white matter tracts of the still functioning areas increase in volume; (3) functional connectivity as a whole is modified as there is a bilateral activation of the middle temporal area as opposed to a controlateral activation in normal vision. This reorganization in the structure and function of the visual pathways correlates with behavioural changes, thus offering a plausible explanation for the blindsight phenomenon.
Meeting abstract presented at VSS 2018
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