Muscle Network of Parkinson's Gait: A 12-Month Longitudinal Analysis Before and After Deep Brain Stimulation Surgery

Bilateral Deep Brain Stimulation (DBS) of the subthalamic nucleus is commonly used for treating motor symptoms in patients with advanced Parkinson's Disease (PD). The aim of this study is to quantitatively and non-invasively evaluate motor control changes in PD patients following DBS through an approach based on the combination of graph theory and frequency-domain electromyography (EMG) analysis. Instrumented gait analysis was carried out on a group of 30 PD patients and 30 age-matched controls. PD patients were longitudinally followed up, with assessments pre-DBS implant ( $\mathrm{T}_{{0}}\text {)}$ , 3 months post-DBS implant ( $\mathrm{T}_{{1}}\text {)}$ , and 12 months post-DBS implant ( $\mathrm{T}_{{2}}\text {)}$ . EMG signals from 12 lower-limb and trunk muscles were acquired, calculating Inter-Muscular Coherence (IMC) for each muscle pair. Adjacency matrices derived from IMC were used to generate 3D muscle networks through a force-based algorithm. Two families of network parameters were extracted: global metrics (modularity and density) and local metrics (node strength and local clustering coefficient). Muscle network modularity of PD patients at T0 was significantly lower than that of controls ( $0.34{\,}\pm{\,}0.07$ vs. $0.41{\,}\pm{\,}0.07$ ; ${p} =0.003$ ) and this difference persisted at T1 ( $0.35{\,}\pm{\,}0.01$ ; ${p} =0.037$ ), but not at T2 ( $0.38{\,}\pm{\,}0.01$ ; ${p} =1.00$ ). Analogously, muscle network density was higher in PD patients at T0 (T0: $0.69{\,}\pm{\,}0.10$ vs. Controls: $0.56{\,}\pm{\,}0.10$ ; ${p} =0.004$ ), decreased at T1 ( $0.65{\,}\pm{\,}0.14$ ; ${p} =0.034$ ), and was comparable to that of controls at T2 ( $0.60{\,}\pm{\,}0.14$ ; ${p} =1.00$ ). Node-level analyses similarly showed that PD patients values moved toward control-group reference levels after DBS surgery, reflecting reduced individual muscle connectivity and a more structured pattern of muscle coordination. Global metrics showed a good agreement with respect to the clinical score UPDRS-III. Graph theory applied to EMG analysis opens new perspectives in the study of motor control strategies during gait and confirms the efficacy of DBS in alleviating motor symptoms of PD patients.