Quantitative Analysis of Motor Neuron Activity in Dynamic and Isometric Finger Flexion and Extension

Dexterous finger movements play an indispensable role in versatile daily activities, largely attributed to the complex neural modulation process. However, quantifying motor neuron activity under different finger movements has not been fully investigated. We thus proposed a non-invasive assessment framework to quantitatively examine motor neuron activities during cyclical flexion/extension movements of the index, middle, and ring finger, considering dynamic and isometric muscle contractions. First, principal component analysis was deployed to evaluate the motor unit (MU) synaptic common drive input. Second, a silhouette-based metric was proposed to compare the similarity of MU spatial distributions across different finger movements. Experimental results showed that, on average, the first principal component of decoded MU spike trains explained a variance of 69.3%, demonstrating a low-dimensional control across these finger movements. In addition, we found that the spatial activation patterns of the index, middle, and ring fingers during flexion were less distinguishable than those during extension. These findings offer insights into the neural control mechanisms underlying finger movements from a microscopic perspective, potentially contributing to advancements in post-stroke rehabilitation, hand-exoskeleton control, and assistive technologies.