Frontal aperiodic activity and sensorimotor theta clustering are differentially modulated by tDCS during...

Proprioceptive deficits are a core feature of Parkinson's disease (PD), but the neural mechanisms by which transcranial direct current stimulation (tDCS) may augment proprioceptive learning remain unknown. This study investigated whether six sessions of anodal tDCS combined with proprioceptive training modulates EEG‑derived aperiodic activity, Lempel‑Ziv complexity (LZC), and theta clustering in individuals with PD. Twenty‑four participants with mild‑to‑moderate PD were randomly assigned to active (2 mA, 20 min) or sham tDCS over the supplementary motor area, combined with a proprioceptive exercise protocol (three sessions/week for two weeks). EEG was recorded during quiet standing with eyes closed before and after the intervention. Aperiodic exponent, aperiodic offset, LZC, and theta clustering were extracted from frontal and central lobes. Significant group×time interactions were observed in the frontal lobe for aperiodic exponent (p=0.022), aperiodic offset (p=0.005), and LZC (p<0.001). The sham group showed flattening of the aperiodic exponent, reduced offset, and increased LZC (+108%), while the active tDCS group remained stable or decreased. In the central lobe, significant interactions were found for LZC (p=0.035) and theta clustering (p=0.014), with the sham group increasing and the active group decreasing on both metrics. No significant interactions were observed in parietal, temporal, occipital, or global parameters. tDCS may serve as a valuable adjunct to proprioceptive rehabilitation in PD by accelerating the transition from effortful, compensatory processing to automatic, efficient sensorimotor control potentially enhancing balance and gait training, reducing fall risk, and informing mechanism-based neurorehabilitation. EEG-derived aperiodic and complexity metrics may serve as biomarkers of intervention response.