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.
- Analysis of Variance
- Brain Mapping
- Evoked Potentials, Motor
- Functional Laterality
- Image Processing, Computer-Assisted
- Functional magnetic resonance imaging
- Motor Cortex
- Muscle Contraction
- Neural Inhibition
- Principal Component Analysis
- Recruitment, Neurophysiological
- Transcranial Magnetic Stimulation
- Young Adult
- Journal Article
- Research Support, Non-U.S. Gov't
- Ipsilateral primary motor cortex co-activation
- Interhemispheric inhibition
- Homogeneous muscle