Assessing the usage of indirect motor pathways following a hemiparetic stroke

Abstract

A hallmark impairment in a hemiparetic stroke is a loss of independent joint control resulting in abnormal co-activation of shoulder abductor and elbow flexor muscles in their paretic arm, clinically known as the flexion synergy. The flexion synergy appears while generating shoulder abduction (SABD) torques as lifting the paretic arm. This likely be caused by an increased reliance on contralesional indirect motor pathways following damage to direct corticospinal projections. The assessment of functional connectivity between brain and muscle signals, i.e., brain-muscle connectivity (BMC), may provide insight into such changes to the usage of motor pathways. Our previous model simulation shows that multi-synaptic connections along the indirect motor pathway can generate nonlinear connectivity. We hypothesize that increased usage of indirect motor pathways (as increasing SABD load) will lead to an increase of nonlinear BMC. To test this hypothesis, we measured brain activity, muscle activity from shoulder abductors when stroke participants generate 20% and 40% of maximum SABD torque with their paretic arm. We computed both linear and nonlinear BMC between EEG and EMG. We found dominant nonlinear BMC at contralesional/ipsilateral hemisphere for stroke, whose magnitude increased with the SABD load. These results supported our hypothesis and indicated that nonlinear BMC could provide a quantitative indicator for determining the usage of indirect motor pathways following a hemiparetic stroke.

Cortical Reorganization of Early Somatosensory Processing in Hemiparetic Stroke

“…This reorganization is likely due to the increased recruitment of ipsilateral cortical regions during the processing of the somatosensory signals from the paretic hand. This is consistent with neuroimaging studies that have demonstrated increased ipsilateral cortical sensorimotor activity during movement [6][7][8]34], which may require the sensory signal to re-route to provide sensory feedback for ipsilateral motor control.…”

“…ERP voltage maps were calculated and drawn at the mean latency of each component. The standardized low-resolution electromagnetic tomographic analysis, sLORETA (v20200701) was used to localize the ERP source activity on the cortex [27,28] The laterality index was computed to investigate the hemisphere dominance of cortical response in the time window of the P50-N100 [29,30]. The LI is defined as the signal power difference between contralateral and ipsilateral hemispheres in the sensorimotor areas (including C1/2, C3/4, C5/6, CP1/2, CP3/4, CP5/6 in 10/20 EEG recording system) and then normalized by their sum, as shown in the equation below.…”

“…The increased activity ipsilateral to brain lesion motor is likely related to a greater reliance on ipsilateral cortico-bulbospinal pathways following stroke-induced damage to contralateral motor pathways at the lesioned [7]. Previous studies found that increased reliance on contralesional descending corticoreticulospinal pathways [7,[9][10][11][12][13] likely accounts for post-stroke movement impairment such as abnormal flexion synergy [14] and spasticity [13,15,16].…”

Multi-phase locking value: A generalized method for determining instantaneous multi-frequency phase coupling

“…In real applications, different numerical values could be used based on real experimental data. For example, we applied M-PLV to check 1:1 (integer) and 2:1 (1/2 non-integer) coupling and estimated delay between electroencephalography (EEG) and electromyography (EMG) signals during a motor task to demonstrate a real application of M-PLV (see Section III C), where the numerical values are from the real data obtained in a human subject experiment [23].…”

“…We tested M-PLV on two scenarios where synthetic coupled signals are generated using white Gaussian signals, and a system comprised of multiple coupled Rössler oscillators. The real application of M-PLV was demonstrated in a EEG-EMG data dataset recorded from human subjects during a motor task [23].…”