Reducing the Impact of Shoulder Abduction Loading on the Classification of Hand Opening and Grasping in Individuals with Poststroke Flexion Synergy

Abstract

Application of neural machine interface in individuals with chronic hemiparetic stroke is regarded as a great challenge, especially for classification of the hand opening and grasping during a functional upper extremity movement such as reach-to-grasp. The overall accuracy of classifying hand movements, while actively lifting the paretic arm, is subject to a significant reduction compared to the accuracy when the arm is fully supported. Such a reduction is believed to be due to the expression of flexion synergy, which couples shoulder abduction (SABD) with elbow/wrist and finger flexion, and is common in up to 60% of the stroke population. Little research has been done to develop methods to reduce the impact of flexion synergy on the classification of hand opening and grasping. In this study, we proposed a novel approach to classify hand opening and grasping in the context of the flexion synergy using a wavelet coherence-based filter. We first identified the frequency ranges where the coherence between the SABD muscle and wrist/finger flexion muscles is significant in each participant, and then removed the synergy-induced electromyogram (EMG) component with a subject-specific and muscle-specific coherence-based filter. The new approach was tested in 21 stroke individuals with moderate to severe motor impairments. Employing the filter, 14 participants gained improvement in classification accuracy with a range of 0.1 to 14%, while four showed 0.3 to 1.2% reduction. The remaining three participants were excluded from comparison due to the lack of significant coherence, thus no filters were applied. The improvement in classification accuracy is significant (p = 0.017) when the SABD loading equals 50% of the maximal torque. Our findings suggest that the coherence-based filters can reduce the impact of flexion synergy by removing the synergy-induced EMG component and have the potential to improve the overall classification accuracy of hand movements in individuals with poststroke flexion synergy.

Improving Hand Function of Severely Impaired Chronic Hemiparetic Stroke Individuals Using Task-Specific Training With the ReIn-Hand System: A Case Series

“…The ReIn-Hand platform wirelessly and simultaneously measures surface EMG activities from eight upper limb muscles, including deltoid, biceps brachii, triceps, extensor communis digitorum, extensor carpi radialis, flexor digitorum profundus, flexor carpi radialis, and abductor pollicis. The device uses subject-dependent coherence-based notch filter to increase the signal-to-noise ratio of the collected EMG signals ( 32 ); it then uses the mean absolute value, zero crossing, slope sign changes, waveform length values ( 33 ) to perform real-time detection of hand opening with or without activation of the shoulder/elbow muscles during functional upper limb motor tasks ( 31 ). Once hand opening is detected, a signal is sent to trigger the electrical stimulator to assist paretic hand opening.…”

Temporal control of muscle synergies is linked with alpha‐band neural drive

“…We hypothesized a direct relationship between EMG amplitude correlation and intermuscular coherence across pairs of muscles, especially within the alpha (8-16 Hz) band. Coherence in this frequency band is highest in tasks requiring precise muscle coordination (de Vries et al 2016;, and is amplified among muscles pathologically coupled after stroke (Lan et al 2017;Chen et al 2018a). Extending this logic, we expected that a multi-muscle synergy derived from EMG amplitudes would closely mirror one derived entirely from multi-muscle alpha-band coherence, since this would occur if these measures characterize different features of the same common neural drive controlling a synergy.…”

“…We recorded EMG activity from seven upper limb muscles while participants rotated a crank in the horizontal plane. Because shoulder abduction exacerbates pathological synergies and associated intermuscular coherence after stroke (Ellis et al 2017;Lan et al 2017), participants repeated the task with two levels of shoulder abduction, allowing this interaction, and posture dependence in general, to be explored in non-disabled adults. We first compared pairwise EMG amplitude correlations and coherence within and between shoulder postures.…”

Assessing the usage of indirect motor pathways following a hemiparetic stroke

“…The flexion synergy appears while generating shoulder abduction (SABD) torques [9, 10] when lifting the weight of the arm or more. It is thought to be caused by progressive recruitment of contralesional indirect motor pathways via the brainstem as a function of SABD effort following a stroke-induced loss of ipsilesional corticospinal projections [2, 11, 12].…”