Cerebral Cortex Advance Access published online on March 3, 2007
Cerebral Cortex, doi:10.1093/cercor/bhm013
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Imaging the Brain Activity Changes Underlying Impaired Visuospatial Judgments: Simultaneous fMRI, TMS, and Behavioral Studies
1 Department of Cognitive Neuroscience, Faculty of Psychology, Maastricht University, 6200 MD Maastricht, The Netherlands, 2 Department of Neurophysiology, Max Planck Institute for Brain Research, 60528 Frankfurt am Main, Germany, 3 Brain Imaging Center Frankfurt, 60590 Frankfurt am Main, Germany, 4 Sobell Department of Motor Neuroscience and Movement Disorders and Wellcome Department of Imaging Neuroscience, University College London, London WC1N 3BG, UK, 5 School of Psychology, University of Wales, Bangor, UK, 6 MR-Research in Neurology and Psychiatry, Georg-August-University Goettingen, 37075 Goettingen, Germany
Address correspondence to Alexander T. Sack, PhD, Department of Cognitive Neuroscience, Faculty of Psychology, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands. Email: a.sack{at}psychology.unimaas.nl.
Damage to parietal cortex impairs visuospatial judgments. However, it is currently unknown how this damage may affect or indeed be caused by functional changes in remote but interconnected brain regions. Here, we applied transcranial magnetic stimulation (TMS) to the parietal cortices during functional magnetic resonance imaging (fMRI) while participants were solving visuospatial tasks. This allowed us to observe both the behavioral and the neural effects of transient parietal activity disruption in the active healthy human brain. Our results show that right, but not left, parietal TMS impairs visuospatial judgment, induces neural activity changes in a specific right-hemispheric network of frontoparietal regions, and shows significant correlations between the induced behavioral impairment and neural activity changes in both the directly stimulated parietal and remote ipsilateral frontal brain regions. The revealed right-hemispheric neural network effect of parietal TMS represents the same brain areas that are functionally connected during the execution of visuospatial judgments. This corroborates the notion that visuospatial deficits following parietal damage are brought about by a perturbation of activity across a specific frontoparietal network, rather than the lesioned parietal site alone. Our experiments furthermore show how concurrent fMRI and magnetic brain stimulation during active task execution hold the potential to identify and visualize networks of brain areas that are functionally related to specific cognitive processes.
Key Words: functional magnetic resonance imaging • parietal cortex • simultaneous TMS-fMRI • transcranial magnetic stimulation • visuospatial processing
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