Differentiation in theta and gamma activation in weight-shifting learning between people with parkinson's disease of different anxiety severities

Anxiety and postural control deficits may be related in people with Parkinson's disease (PwPD). However, the association between anxiety levels and weight-shifting control remains ambiguous. This study investigated whether 1) weight-shifting control differed between PwPD with and without anxiety, and 2) the learning effect of weight-shifting differed between the two populations. Additionally, we evaluated cortical activities to investigate neural mechanisms underlying weight-shifting control. Twenty-eight PwPD (14 anxiety, 14 nonanxiety) participated in a 5-day weight-shifting study by coupling the bearing weight of their more-affected leg to a sinusoidal target at 0.25 Hz. We tested the weight-shifting control on day 1 (pretest), day 3 (posttest), and day 5 (retention test) with a learning session on day 3. The error and jerk of weight-shifting trajectory and the theta and gamma powers of electroencephalography in prefrontal, frontal, sensorimotor and parietal-occipital areas were measured. At the pretest, the anxiety group showed larger error and smaller jerk of weight-shifting with greater prefrontal theta, frontal gamma, and sensorimotor gamma powers than the nonanxiety group. Anxiety intensity was correlated positively with weight-shifting error and theta power but negatively with weight-shifting jerk. Reduced weight-shifting error with increased theta power after weight-shifting learning was observed in the nonanxiety group. However, the anxiety group showed decreased gamma power after weight-shifting learning without behavior change. Our findings suggest differential weight-shifting control and associated cortical activation between PwPD with and without anxiety. In addition, anxiety would deteriorate weight-shifting control and hinder weight-shifting learning benefits in PwPD, leading to less weight-shifting accuracy and correction.