title: Abnormal interhemispheric motor interactions in patients with callosal agenesis.
abstract: During unilateral hand movements the activity of the contralateral primary motor cortex (cM1) is increased while the activity of the ipsilateral M1 (iM1) is decreased. A potential explanation for this asymmetric activity pattern is transcallosal cM1-to-iM1 inhibitory control. To test this hypothesis, we examined interhemispheric motor inhibition in acallosal patients. We measured fMRI activity in iM1 and cM1 in acallosal patients during unilateral hand movements and compared their motor activity pattern to that of healthy controls. In controls, fMRI activation in cM1 was significantly higher than in iM1, reflecting a normal differential task-related M1 activity. Additional functional connectivity analysis revealed that iM1 activity was strongly suppressed by cM1. Furthermore, DTI analysis indicated that this contralaterally induced suppression was mediated by microstructural properties of specific callosal fibers interconnecting both M1s. In contrast, acallosal patients did not show a clear differential activity pattern between cM1 and iM1. The more symmetric pattern was due to an elevated task-related iM1 activity in acallosal patients, which was significantly higher than iM1 activity in a subgroup of gender and age-matched controls. Also, interhemispheric motor suppression was completely absent in acallosal patients. These findings suggest that absence of callosal connections reduces inhibitory interhemispheric motor interactions between left and right M1. This effect may reveal novel aspects of mechanisms in communication of two hemispheres and establishment of brain asymmetries in general.
authors.affiliation: Ruhr University Bochum, Biopsychology, GAFO 05/620, D-44780 Bochum, Germany; Department of Neurophysiology, Max Planck Institute for Brain Research, Deutschordenstr. 46, D-60528 Frankfurt am Main, Germany; Brain Imaging Center Frankfurt, Schleusenweg 2-16, D-60528 Frankfurt am Main, Germany; Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Deutschordenstr. 46, Frankfurt am Main D-60528, Germany. Electronic address: erhan.genc@rub.de.
authors.forename: Erhan
authors.initials: E
authors.lastname: Genç
authors.affiliation: Ruhr University Bochum, Biopsychology, GAFO 05/620, D-44780 Bochum, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Ocklenburg
authors.affiliation: Department of Neurophysiology, Max Planck Institute for Brain Research, Deutschordenstr. 46, D-60528 Frankfurt am Main, Germany; Brain Imaging Center Frankfurt, Schleusenweg 2-16, D-60528 Frankfurt am Main, Germany; Ernst Strüngmann Institute (ESI) for Neuroscience in Cooperation with Max Planck Society, Deutschordenstr. 46, Frankfurt am Main D-60528, Germany; Frankfurt Institute for Advanced Studies, Goethe University, Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main, Germany.
authors.forename: Wolf
authors.initials: W
authors.lastname: Singer
authors.affiliation: Ruhr University Bochum, Biopsychology, GAFO 05/620, D-44780 Bochum, Germany.
authors.forename: Onur
authors.initials: O
authors.lastname: Güntürkün
mesh_terms: D000293:Adolescent; D000328:Adult; D061085:Agenesis of Corpus Callosum / Q000150:complications* / Q000473:pathology; D000704:Analysis of Variance; D001931:Brain Mapping; D016022:Case-Control Studies; D003337:Corpus Callosum / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000473:pathology; D011596:Psychomotor Disorders / Q000209:etiology*; D055815:Young Adult
keywords: Corpus callosum agenesis; DTI; Interhemispheric inhibition; Motor cortex; fMRI