Restoration of temporal separability between beta and movement ensemble co-firing with motor recovery

Abstract

Stroke disrupts movement control by damaging descending motor pathways, yet the cortical dynamics underlying recovery remain poorly defined. Using a non-human primate model of primary motor cortex injury with impaired reach-to-grasp control, we examined how dorsal premotor cortex (PMd) activity supports recovery. Specifically, we studied the interaction between beta activity (12-30 Hz), often linked to "idle" states, and execution-related ensemble co-firing quantified with dimensionality reduction. Stroke impaired the temporal separability between beta bursts and movement-related co-firing, leading to slower reaction times and reduced performance. Recovery was associated with increased separability, and during grasping, beta activity progressively declined with recovery. These results indicate that reliable transitions between high-beta idle and high co-firing execution states are important for movement control, whereas pathological beta intrusions during execution degrade performance. Importantly, low-frequency alternating current stimulation (ACS) via a ringtrode interface enhanced temporal separability and improved reach-to-grasp performance, highlighting a potential therapeutic strategy.

Keywords: alternating current stimulation; beta; co-firing; movement; non-human primate; orthogonal; preparation; separability; stroke.