Effects of light therapy on sleep and anxiety in Parkinson's disease: A pilot trial

Light therapy (LT) may improve sleep and affective disorders in Parkinson's disease (PD), but effects of different intensities and underlying mechanisms remain unclear.

Thirty-three patients with PD were randomized to receive either 1 month of bright LT (BLT) at 10000 lx or dim LT (DLT) at 200 lx, separated by a 1-month washout period, in a crossover fashion. All patients completed clinical assessments, polysomnography (PSG) and resting-state electroencephalogram (EEG) at baseline and after each intervention period. Functional connectivity was assessed using weighted Phase Lag Index (wPLI).

Both BLT and DLT significantly reduced Pittsburgh Sleep Quality Index (PSQI). BLT showed a greater reduction in Epworth Sleepiness Scale (ESS) (P = 0.009), whereas DLT showed a greater reduction in Hamilton Anxiety Rating Scale (HAMA) (P = 0.030). In within-treatment comparisons, BLT was associated with increased slow wave energy (P = 0.001) and theta-band wPLI between specific visual network(VN) pairs, while DLT was associated with increased slow wave sleep proportion (P = 0.006) and alpha-band mean default mode network (DMN) wPLI. However, between-treatment comparisons revealed no significant differences in any PSG or EEG outcomes.

BLT showed greater improvement in daytime sleepiness than DLT, while DLT showed greater reduction in anxiety than BLT. For brain networks, BLT showed significant within-treatment improvement in the visual network, and DLT showed significant within-treatment improvement in the DMN. However, between-treatment comparisons did not reveal significant differences. The hypothesis that different intensities of LT affect different brain networks warrants further validation.