Abstract

SA.15.07

Abnormal visual field representations in albinism – visual processing beyond the primary visual cortex

Michael B. Hoffmann1, Martin Kanowski2, Synke Meltendorf3, Wolfgang Behrens-Baumann3, Barbara Wolysnki1
1Visual Processing Laboratory, Universitäts-Augenklinik, Universität Magdeburg, Magdeburg, 2Neurologie, Otto-von-Guericke-Universität Magdeburg, 3Universitäts-Augenklinik, Otto-von-Guericke-Universität Magdeburg

Objective
Processing of a visual stimulus for motor responses activates an extensive cortical network [1]. In albinism, this is accomplished with an abnormal input of the ipsilateral visual field to the primary visual cortex (V1), which is due to the misprojection of part of the temporal retina to the contralateral hemisphere [2,3]. With functional magnetic resonance imaging (fMRI) visuo-motor processing with an abnormal visual field representation was investigated.
Methods
14 patients with albinism and 14 controls were investigated with fMRI at 3 Tesla. During the scans the subjects solved a visuo-motor task: During monocular central fixation a coloured target (red or blue) embedded in a blinking array of distractors (6.5°x6.5°; centred 5.5° lateral) was presented for 250 ms in either the left or right hemifield. After a variable delay the subjects pressed the upper and lower key for targets in the upper and lower field, respectively, with the right or left thumb for red and blue targets, respectively. A separate analysis of fMRI responses was conducted for visual stimulation and for motor activity.
Results
Controls and patients had equal performance in the visuo-motor task with a hit rate of 96% each. In seven patients with albinism a strong abnormality of the visual field representation was evident. While this abnormality reached into the intraparietal sulcus, lateralisation patterns in the somatosensory and motor cortex were unaffected.
Conclusions
In albinism a visuo-motor task can be solved with an abnormal visual field represenation that affects great expands of the occipito-parietal cortex. This integration of abnormal input for visuo-motor processing highlights the plasticity of this system.

[1] Wolynski B, Schott BH, Kanowski M, Hoffmann MB (2009) Visuo-motor integration in humans: Cortical patterns of response lateralisation and functional connectivity. Neuropsychologia 47:1313-22
[2] Apkarian P, Reits D, Spekreijse H, Van Dorp D (1983) A decisive electrophysiological test for human albinism. EEG & Clin Neurophysiol 55: 513-531
[3] Hoffmann MB, Tolhurst DJ, Moore AT, Morland AB (2003) Organisation of the visual cortex in human albinism. J Neuroscience 23:8921-8930

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