Related Experiment Video
Updated: May 13, 2026

An Experiment Using Functional Near-Infrared Spectroscopy and Robot-Assisted Multi-Joint Pointing Movements of the Lower Limb
Published on: June 7, 2024
Co-activation of primary motor cortex ipsilateral to muscles contracting in a unilateral motor task
Shin-Yi Chiou1, Ray-Yau Wang, Kwong-Kum Liao
1Department of Physical Therapy and Assistive Technology, National Yang-Ming University, Taipei, Taiwan.
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.
More Related Videos
Related Concept Videos
Motor and Sensory Areas of the Cortex
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex.
Muscle Coordination and Action
Agonists
Agonist muscles, often called prime movers, are the primary muscles responsible for producing a specific movement.
Muscle Contraction
Muscle Contraction
Somatosensory, Motor, and Association Cortex
Motor Unit Stimulation
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...

