Researchers reporting in a 2026 open‑access paper found that cortical beta rhythms separately track directional uncertainty and movement preparation, and that beta‑frequency repetitive transcranial magnetic stimulation (rTMS) can speed movement initiation when timed to the oscillation’s trough.

In a study of 24 healthy, right‑handed adults, EEG recorded bilateral beta power (13–30 Hz) during a cued reaching task with three uncertainty levels. The authors report that higher uncertainty produced smaller reductions in beta power (i.e., relatively elevated beta) across both hemispheres. In contrast, movement‑related beta modulation was lateralised to the hemisphere contralateral to the moving hand, and higher pre‑go beta power predicted longer reaction times (RTs).

The team delivered 10 pulses of rTMS during the preparatory period at each participant’s individual beta frequency (mean IBF 20.44 ± 0.38 Hz), using stimulation intensity set at 90% of active motor threshold (mean AMT 51.81% of stimulator output). Both regular (rhythmic at IBF) and irregular rTMS shortened RTs and reduced the magnitude of beta event‑related desynchronisation (ERD). ERD is the drop in beta power that normally precedes movement; smaller ERD here correlated with faster RTs, which the authors interpret as lowering a neural threshold for action.

The behavioural effect was phase‑dependent for regular rTMS. When regular rTMS began during the beta ‘‘down state’’ (defined by the authors as initial phase between –π and –π/4), RTs were significantly shorter than for irregular rTMS (coefficient k = 0.0027 ± 0.0013, P = 0.0352). The paper reports no clear phase effect for irregular stimulation and no reliable difference in ERD between phase bins despite the RT change.

The authors note limitations: low‑density EEG, subthreshold rTMS that did not produce motor‑evoked potentials, and a post hoc phase analysis. They suggest the results support physiologically informed timing of non‑invasive stimulation and note possible relevance to disorders with beta dysregulation such as Parkinson’s disease, while stopping short of clinical claims.

Photo credit: ars.els-cdn.com

Tags: beta oscillations, rTMS, motor control, EEG, phase-dependent stimulation

Topics: Non-invasive brain stimulation, Neuromodulation, Neuroscience & neuroplasticity