The Journal of Neuroscience, July 18, 2007, 27(29):7847-7853; doi:10.1523/JNEUROSCI.1299-07.2007
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Behavioral/Systems/Cognitive
Can Left-Handedness be Switched? Insights from an Early Switch of Handwriting
Stefan Klöppel,1,2,4
Anna Vongerichten,1
Thilo van Eimeren,1,3
Richard S. J. Frackowiak,2,5,6 and
Hartwig R. Siebner1,7
1NeuroImage-Nord, Hamburg-Lübeck-Kiel, Germany, 2Wellcome Trust Centre for Neuroimaging, University College London, London WC1N 3BG, United Kingdom, 3Department of Neurology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany, 4Department of Neurology, Neurozentrum, University Clinic Freiburg, 79106 Freiburg, Germany, 5Laboratory of Neuroimaging, IRCCS Santa Lucia, 00179 Rome, Italy, 6Departement d'Etudes Cognitives, Ecole Normale Superieure, 75005 Paris, France, and 7Department of Neurology, Christian-Albrechts-University, 24105 Kiel, Germany
Correspondence should be addressed to Dr. Stefan Klöppel, Wellcome Trust Centre for Neuroimaging, 12 Queen Square, London WC1N 3BG, UK. Email: s.kloppel{at}fil.ion.ucl.ac.uk
"Converted" left-handers are innately left-handed individuals forced as children to write with the right nondominant hand. We asked how a left-to-right handwriting switch shapes cortical sensorimotor representations of finger movements. In 16 adult converted left-handers and age-matched groups of 16 consistent right-handers and 16 left-handers, we studied movement-related neuronal activity with functional magnetic resonance imaging while participants performed simple unimanual and bimanual movements with right and left index fingers. In converted left-handers, movement-related activity in the primary sensorimotor hand area (SM1) and caudal dorsal premotor cortex (PMd) of the nondominant left hemisphere correlated with the left-to-right shift in handedness. The more right-handed converted left-handers had become, the greater the sensorimotor activation in these areas. Between-group comparisons showed that the switch from left to right hand also reinforced movement representations in the dominant right hemisphere. In converted left-handers, the right inferior parietal cortex and lateral PMd were more active relative to consistent right or left-handers in all motor tasks. These results suggest two distinct neuronal correlates of handedness in human sensorimotor cortex. Although those in executive sensorimotor cortex (i.e., SM1 and adjacent PMd) depend on the hand used throughout life, those in higher-order sensorimotor areas (i.e., inferior parietal cortex and rostrolateral PMd) are invariant and thus cannot be switched to the nondominant hemisphere by educational training.
Key words: handedness; converted left-handers; fMRI; motor control; parietal; plasticity
Received Nov. 24, 2006;
revised June 9, 2007;
accepted June 11, 2007.
Correspondence should be addressed to Dr. Stefan Klöppel, Wellcome Trust Centre for Neuroimaging, 12 Queen Square, London WC1N 3BG, UK. Email: s.kloppel{at}fil.ion.ucl.ac.uk
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