title: The compensatory dynamic of inter-hemispheric interactions in visuospatial attention revealed using rTMS and fMRI.
abstract: A balance of mutual tonic inhibition between bi-hemispheric posterior parietal cortices is believed to play an important role in bilateral visual attention. However, experimental support for this notion has been mainly drawn from clinical models of unilateral damage. We have previously shown that low-frequency repetitive TMS (rTMS) over the intraparietal sulcus (IPS) generates a contralateral attentional deficit in bilateral visual tracking. Here, we used functional magnetic resonance imaging (fMRI) to study whether rTMS temporarily disrupts the inter-hemispheric balance between bilateral IPS in visual attention. Following application of 1 Hz rTMS over the left IPS, subjects performed a bilateral visual tracking task while their brain activity was recorded using fMRI. Behaviorally, tracking accuracy was reduced immediately following rTMS. Areas ventro-lateral to left IPS, including inferior parietal lobule (IPL), lateral IPS (LIPS), and middle occipital gyrus (MoG), showed decreased activity following rTMS, while dorsomedial areas, such as Superior Parietal Lobule (SPL), Superior occipital gyrus (SoG), and lingual gyrus, as well as middle temporal areas (MT+), showed higher activity. The brain activity of the homologues of these regions in the un-stimulated, right hemisphere was reversed. Interestingly, the evolution of network-wide activation related to attentional behavior following rTMS showed that activation of most occipital synergists adaptively compensated for contralateral and ipsilateral decrement after rTMS, while activation of parietal synergists, and SoG remained competing. This pattern of ipsilateral and contralateral activations empirically supports the hypothesized loss of inter-hemispheric balance that underlies clinical manifestation of visual attentional extinction.
authors.affiliation: Department of Biomedical Engineering and Department of Physical Medicine and Rehabilitation, Cleveland Clinic Cleveland, OH, USA ; Department of Neurology, Beth Israel Deaconess Medical Center, Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School Boston, MA, USA.
authors.forename: Ela B
authors.initials: EB
authors.lastname: Plow
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School Boston, MA, USA ; Department of Psychology, University of Milano-Bicocca Milano, Italy ; Brain Connectivity Center, National Neurological Institute C. Mondino Pavia, Italy.
authors.forename: Zaira
authors.initials: Z
authors.lastname: Cattaneo
authors.affiliation: Department of Cognitive Science, Macquarie University Sydney, NSW, Australia ; Department of Psychology, Harvard University Cambridge, MA, USA.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Carlson
authors.affiliation: Department of Psychology, Harvard University Cambridge, MA, USA.
authors.forename: George A
authors.initials: GA
authors.lastname: Alvarez
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School Boston, MA, USA ; Instituto Guttmann de Neurorrehabilitación, Universidad Autónoma de Barcelona Badalona, España.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.affiliation: Department of Neurology, Beth Israel Deaconess Medical Center, Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School Boston, MA, USA ; Center for Neuroscience and Cognitive Systems@UniTn, Fondazione Istituto Italiano di Tecnologia Rovereto, Italy.
authors.forename: Lorella
authors.initials: L
authors.lastname: Battelli
keywords: TMS; fMRI; inter-hemispheric interaction; visual extinction; visuospatial attention