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Cerebral Cortex Advance Access published online on April 15, 2008
Cerebral Cortex, doi:10.1093/cercor/bhn053
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© 2008 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Hemispheric Asymmetry of Frequency-Dependent Suppression in the Ipsilateral Primary Motor Cortex During Finger Movement: A Functional Magnetic Resonance Imaging Study

Masamichi J. Hayashi1,2, Daisuke N. Saito2,3, Yu Aramaki2,3,4, Tatsuya Asai5, Yasuhisa Fujibayashi5 and Norihiro Sadato1,2,3,5

1 Department of Physiological Sciences, The Graduate University for Advanced Studies (Sokendai), Okazaki, Japan, 2 National Institute for Physiological Sciences, Okazaki, Japan, 3 Japan Science and Technology Corporation/Research Institute of Science and Technology for Society, Kawaguchi, Japan, 4 Computational Neuroscience Sub-Group, Biological ITC Group, National institute of Information and Communications Technology, Kyoto, Japan, 5 Biomedical Imaging Research Center, University of Fukui, Fukui, Japan

Address correspondence to Norihiro Sadato, MD, PhD, Section of Cerebral Integration, Department of Cerebral Research, National Institute for Physiological Sciences, Myodaiji, Okazaki, Aichi 444-8585, Japan. Email: sadato{at}nips.ac.jp.

Electrophysiological studies have suggested that the activity of the primary motor cortex (M1) during ipsilateral hand movement reflects both the ipsilateral innervation and the transcallosal inhibitory control from its counterpart in the opposite hemisphere, and that their asymmetry might cause hand dominancy. To examine the asymmetry of the involvement of the ipsilateral motor cortex during a unimanual motor task under frequency stress, we conducted block-design functional magnetic resonance imaging with 22 normal right-handed subjects. The task involved visually cued unimanual opponent finger movement at various rates. The contralateral M1 showed symmetric frequency-dependent activation. The ipsilateral M1 showed task-related deactivation at low frequencies without laterality. As the frequency of the left-hand movement increased, the left M1 showed a gradual decrease in the deactivation. This data suggests a frequency-dependent increased involvement of the left M1 in ipsilateral hand control. By contrast, the right M1 showed more prominent deactivation as the frequency of the right-hand movement increased. This suggests that there is an increased transcallosal inhibition from the left M1 to the right M1, which overwhelms the right M1 activation during ipsilateral hand movement. These results demonstrate the dominance of the left M1 in both ipsilateral innervation and transcallosal inhibition in right-handed individuals.

Key Words: fMRI • inhibition • ipsilateral • motor control • motor cortex • negative BOLD


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