Abstract
Neglect and hemianopia are two neuropsychological syndromes that are associated with reduced awareness for visual signals in patients’ contralesional hemifield. They offer the unique possibility to dissociate the contributions of retino-geniculate and retino-colliculo circuitries in visual perception. Yet, insights from patient fMRI studies are limited by heterogeneity in lesion location and extent, long-term functional reorganization and behavioural compensation after stroke. Transcranial magnetic stimulation (TMS) has therefore been proposed as a complementary method to investigate the effect of transient perturbations on functional brain organization. This concurrent TMS-fMRI study applied TMS perturbation to occipital and parietal cortices with the aim to ‘mimick’ neglect and hemianopia. Based on the challenges and interpretational limitations of our own study we aim to provide tutorial guidance on how future studies should compare TMS to primary sensory and association areas that are governed by distinct computational principles, neural dynamics and functional architecture.
Highlights
Neglect and hemianopia are two neuropsychological syndromes that are associated with reduced awareness for visual signals in patients’ contralesional hemifield
Each trial type was presented with occipital cortex (Occ), IPS- and Sham-Transcranial magnetic stimulation (TMS) resulting in 12 conditions in total
Based on our apriori hypothesis and questions we report activations at the voxel level corrected for multiple comparisons within right IPS and right lower level visual areas (i.e. V1 + V2) as our regions of interest (ROI) where Occ and IPS-TMS were applied
Summary
Neglect and hemianopia are two neuropsychological syndromes that are associated with reduced awareness for visual signals in patients’ contralesional hemifield. While neglect results primarily from right inferior parietal and temporal lesions impairing spatial and temporal attention [1,2,3,4,5], hemianopia is caused by lesions to primary visual cortex leading to selective visual perceptual deficits [6]. Contrasting these two syndromes offers the unique possibility to dissociate retino-geniculate and retino-colliculo circuitries whereby ‘unaware’ visual signals can impact human behaviour [7,8,9]. Patients’ symptoms and neural mechanisms may have changed as a result of long-term functional reorganization and compensatory behavioural adaptation after stroke or other permanent focal lesions
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