Neural changes in early visual cortex after unilateral occipito-temporal stroke and object-recognition deficits M Praß1, C Grimsen2, M Fahle2 |
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1Center of Neurology, University of Tuebingen, Germany |
| Visual object agnosia is a striking symptom following bilateral lesions of occipito-temporal cortices. After unilateral ventral lesions usually no major object recognition deficits occur. We used fMRI to investigate eight stroke patients with unilateral occipito-temporal damage and free visual fields to assess object-categorization performance and corresponding neural correlates. Patients and controls performed a rapid event-related paradigm (animal/non-animal categorization), with images presented left or right of fixation. Lateralized stimulus presentation normally elicits higher cortical activation for contralateral than ipsilateral stimuli (contralateral bias). Regions of interest in early and object-selective visual cortex were delineated using separate mapping paradigms. Previously, we showed that patients yield reduced categorization performance both ipsi- and contralesional, accompanied by altered BOLD responses in object-selective cortex of the lesioned hemisphere (no contralateral bias; Prass et al., 2012, Perception, 41 ECVP Supplement, 104). Here, we report how activity in undamaged early visual cortex is modulated: early areas of the lesioned hemisphere show a reduced contralateral bias. The intact hemisphere was normally activated. The results demonstrate that patients with unilateral lesions and object categorization deficits in both visual fields show altered neural activation even in early (undamaged) visual areas. This suggests that ventral lesions remotely influence structurally intact early visual cortex. |
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