Co-activation of primary motor cortex ipsilateral to muscles contracting in a unilateral motor task

Shin Yi Chiou, Ray Yau Wang, Kwong Kum Liao, Yu Te Wu, Chia Feng Lu, Yea Ru Yang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


Objective: This study aims to investigate the role of the primary motor cortex ipsilateral to the movement (ipsilateral M1) in unilateral motor execution. Methods: Fifteen right-handed healthy subjects underwent functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) experiments. Motor tasks were performed with the right-side limb. Subjects followed visual cues to execute movements in the scanner and independent component analysis (ICA) was applied to analyse the data. Interhemispheric inhibition (IHI), short-interval intracortical inhibition (SICI) and recruitment curves (RCs) of motor-evoked potentials (MEPs) in right M1 were measured by TMS and responses were recorded from the left flexor carpi radialis (FCR) and left anterior deltoid (AD). Results: Group ICA showed activations of bilateral M1s highly related to motor tasks. Additionally, TMS results showed significant increases of MEP RCs on the left FCR and left AD during right wrist flexion and right shoulder flexion. Prominent decreases of IHI and SICI were also observed under the same conditions. Conclusions: During unilateral muscle contraction, co-activation of the ipsilateral M1 involves additional processes modulated by intra- and interhemispheric interactions and its size of activations is specifically enhanced on the homotopic representation. Significance: The ipsilateral M1 plays a central role in unilateral motor executions.

Original languageEnglish
Pages (from-to)1353-1363
Number of pages11
JournalClinical Neurophysiology
Issue number7
StatePublished - Jul 2013


  • Functional magnetic resonance imaging
  • Homogeneous muscle
  • Interhemispheric inhibition
  • Ipsilateral primary motor cortex co-activation
  • Transcranial magnetic stimulation


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