Common and specific effects in brain oscillations and motor symptoms of tDCS and tACS in Parkinson’s disease

Parkinson's disease (PD) leads to neurodegeneration and abnormal brain oscillations, causing motor dysfunction. Transcranial stimulation (transcranial direct current stimulation [tDCS]/transcranial alternating current stimulation [tACS]) may alleviate symptoms, but their oscillatory modulation mechanisms remain unclear. This randomized controlled trial (RCT) examines the effects of single-session tDCS/tACS on 60 PD patients, assigned to tDCS, tACS (20 Hz), or sham groups. Each receives 20-min left motor cortex stimulation while performing a simple reaction task. Open-source resting-state electroencephalogram (EEG) data reveal increased theta and decreased beta power in PD. In the RCT, tDCS and tACS enhance beta power, improving rigidity and bradykinesia. Additionally, tDCS reduces theta power, specifically alleviating tremor symptoms. Notably, the theta/beta ratio predicts and mediates tremor changes induced by tDCS more effectively than theta power alone. This sutdy revealed that tDCS broadly modulates oscillations, improving multiple symptoms, while tACS targets a single oscillation for specific symptom relief, emphasizing the crucial role of diverse oscillations in PD motor pathophysiology. This study was registered at ClinicalTrials.gov (NCT05678725).