Reduced sensorimotor beta dynamics could represent a "slowed movement state" in healthy individuals

Beta oscillations (~13-30 Hz) recorded from the sensorimotor cortex have canonical amplitude changes during movement. Specifically, a movement-related beta decrease (MRBD) occurs before movement, and a post-movement beta rebound (PMBR) follows. We investigated how the MRBD and PMBR vary with movement speed. Individuals performed a task with blocks that generated longer reaction times (RTs) and shorter RTs (Slow and Fast blocks, respectively) while scalp-electroencephalography (EEG) was recorded. The timing of task events before movement was also modulated to generate blocks with certain and uncertain timing (Fixed and Varied blocks, respectively). Beta modulation was reduced in Slow blocks compared to Fast blocks (i.e., a less negative MRBD and less positive PMBR). For the movement certainty manipulation, we saw mixed behavioral and EEG results. Our primary findings align with previous work which has shown reduced movement-related beta modulation in patients with Parkinsons disease. We propose that a "slowed movement state", whether it is experimentally induced or a manifestation of Parkinsons disease bradykinesia, is represented through reduced beta dynamics. Altogether, the MRBD and PMBR may represent motor speed on a continuum with Parkinsons disease as an extreme example of slowed movement.