Movement-related beta modulation in amyotrophic lateral sclerosis depends on muscle strength: A magnetoencephalography study

Movement‑related modulation of the sensorimotor beta‑rhythm (14–30 Hz) reflects aspects of cortical excitability, thalamocortical and local neuronal activity. However, its behavior in amyotrophic lateral sclerosis (ALS) has been explored almost exclusively during self-generated movement. We combined visually cued finger tapping with a pneumatic actuator‑driven, kinematically matched passive paradigm while recording whole‑head magnetoencephalography (MEG) in 11 ALS patients and 12 healthy controls (HC). Mean beta-band power was extracted for rest, event-related desynchronization (ERD) and post-movement rebound (event-related synchronization; ERS), and movement-related modulation was quantified relative to each participant’s rest window. The beta modulations (ERD and ERS) did not differ significantly between ALS patients and HC. However, stratifying ALS patients by hand strength revealed that patients with weakness showed a markedly shallower ERD than patients with preserved strength. The beta modulations (ERD, ERS, and absolute power) did not differ significantly. Movement type (active vs passive) did not significantly interact with grouping (ALS versus HC) and thus we were unable to confirm our hypothesis of abnormal beta modulation only in the active task. ALS does not uniformly attenuate movement-related beta‑power; rather, clinical weakness selectively blunts the desynchronization component of the movement-related beta-modulation, and this attenuation is equally evident during passive proprioceptive stimulation. Passive‑task beta‑modulation therefore could potentially offer an effort‑independent, disease‑severity‑sensitive marker related to muscle strength in ALS.