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

► The role of the primary motor cortex (M1) ipsilateral to the movement and its intra- and interhemispheric interactions with contralateral M1 were studied in right-handed healthy adults during unilateral motor task by right hand and right leg. ► Activations of the ipsilateral M1 highly correlated with motor task and its co-activation not only globally occurred in motor areas but also specifically acted on the homotopic representations. ► Ipsilateral M1 plays a critical role in unilateral motor task and its intracortical and corticospinal responses were associated with interhemispheric modulations by contralateral M1.