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Barbara Wolynski, Martin Kanowski, Michael B. Hoffmann; Response lateralisations in visuo-motor cortex and consequences of abnormal visual input. Journal of Vision 2008;8(6):491. doi: 10.1167/8.6.491.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A dominance of the representation of the contralateral visual field is evident not only in occipital, but also in parietal visual areas. Here we devised a paradigm to activate great expanses of visual, visuo-motor, and motor cortex for a separate assessment of the visual and motor response lateralisations. This paradigm was applied in humans with normal visual input and in albinotic humans with abnormally lateralised input to V1.
Methods: Brain activity was studied during a visuo-motor task in 14 controls and 14 albinotic subjects (3Tesla, Siemens; SPM5; event-related design): While the subjects fixated a central dot monocularly, a coloured target embedded in an array of grey distractors (6.5°×6.5°; centered at 5.5° from fixation) was presented for 250 ms either in the left or right visual hemi-field. After a variable delay the subjects were to indicate the target-location by pressing the upper or lower response button with the left or right thumb for blue and red targets, respectively.
Results: (1) Normal input to V1 resulted in representations of the contralateral visual field in occipital visual areas, in area MT, and in the intraparietal sulcus (IPS1–IPS3). While there was little or no activity in somatosensory (BA1–3) and motor areas (BA4 and BA6) during visual stimulation, these areas responded contralaterally to the effector during the motor response. Early visual areas were also activated during the motor response, remarkably with dominant activities ipsilateral to the preceding visual stimulus. (2) Abnormal input to V1 induced lateralisation abnormalities of responses in occipito-parietal areas during visual stimulation, but left somatosensory- and motor-responses unaltered.
Conclusion: Contralateral visual field representations appear to be a fundamental characteristic not only of occipical, but also of parietal visual areas in humans. However, this representation principle appears to be severely disrupted by abnormally lateralised input to V1 as evident in albinotic subjects.
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