Interhemispheric connectivity during bimanual isometric force generation

Abstract

Interhemispheric interactions through the corpus callosum play an important role in the control of bimanual forces. However, the extent to which physiological connections between primary motor cortices are modulated during increasing levels of bimanual force generation in intact humans remains poorly understood. Here we studied coherence between electroencephalographic (EEG) signals and the ipsilateral cortical silent period (iSP), two well-known measures of interhemispheric connectivity between motor cortices, during unilateral and bilateral 10%, 40%, and 70% of maximal isometric voluntary contraction (MVC) into index finger abduction. We found that EEG-EEG coherence in the alpha frequency band decreased while the iSP area increased during bilateral compared with unilateral 40% and 70% but not 10% of MVC. Decreases in coherence in the alpha frequency band correlated with increases in the iSP area, and subjects who showed this inverse relation were able to maintain more steady bilateral muscle contractions. To further examine the relationship between the iSP and coherence we electrically stimulated the ulnar nerve at the wrist at the alpha frequency. Electrical stimulation increased coherence in the alpha frequency band and decreased the iSP area during bilateral 70% of MVC. Altogether, our findings demonstrate an inverse relation between alpha oscillations and the iSP during strong levels of bimanual force generation. We suggest that interactions between neural pathways mediating alpha oscillatory activity and transcallosal inhibition between motor cortices might contribute to the steadiness of strong bilateral isometric muscle contractions in intact humans.

Corticomuscular control of walking in older people and people with Parkinson’s disease

“…Finally, we calculated bipolar EEG montages based on the monopolar recordings to assess cortical activity from bilateral sensorimotor cortices: C3-F3 for the left sensorimotor cortex, and C4-F4 for the right sensorimotor cortex (cf. Long et al 2015).…”

Antagonist Muscle Prefatigue Increases the Intracortical Communication between Contralateral Motor Cortices during Elbow Extension Contraction

“…In this study, EEG power in the beta frequency band as well as EEG sample entropy and fractal dimension of both left and right motor cortices shows a significant increase in postfatigue contraction than in prefatigue contraction. As movements of the right side of the body are mainly controlled by the left motor cortex of the brain and bilateral connection of upper limb movement [ 17 , 18 ], the increase of EEG power, sample entropy, and fractal dimension in both left and right motor cortices can be easily expected. However, significant phase synchronization index changes were only found between C3 and FC3, indicating that elbow flexion muscle fatigue may only have significant influences on the functional connectivity of the contralateral motor cortex during elbow extension contraction.…”

“…EEG oscillation activity in beta rhythm is associated with motor cortical function [ 17 , 19 , 20 ], and a significant increase of EEG-EMG and EMG-EMG coupling in the beta frequency band induced by muscle fatigue has been revealed in many studies [ 15 , 21 , 22 ]. In this study, a significant increase of the phase synchronization index was found in the beta frequency band between contralateral primary motor cortices, which suggested a significant role for synchronization in the organization and regulation of elbow extension movement within the contralateral primary motor cortex when the antagonist muscle prefatigued.…”

Corticomuscular control of walking in older people and people with Parkinson’s disease

“…The remaining components were retained and projected back onto the channels. Finally, we calculated bipolar EEG montages based on the monopolar recordings to assess cortical activity from bilateral sensorimotor cortices: C3-F3 for the left sensorimotor cortex, and C4-F4 for the right sensorimotor cortex 200 . A differential recording between electrode pairs suppresses far-field contamination and is hence most sensitive to local activity generated between the electrode pairs.…”