Transcranial direct current stimulation of supplementary motor area improves upper limb kinematics in Parkinson’s disease

Bradykinesia, defined as slowness of movements, is among the most functionally debilitating symptoms of Parkinson's disease (PD). Hypoactivation of cortical neurons in supplementary motor area (SMA) has been linked to the progression of bradykinesia symptoms. This study investigated the influence of transcranial direct current stimulation (tDCS) applied over SMA on upper limb movement for individuals diagnosed with PD.Thirteen individuals with PD performed a simple reaction time (RT) task involving elbow extension following an auditory go-signal. Sham or anodal tDCS was then applied over SMA for 10 minutes before participants repeated the simple RT task. Participants were unaware of which stimulation they received in each testing session. Electromyography (EMG) and kinematic data were recorded on all trials.While there were no significant differences in premotor RT, anodal tDCS applied over SMA led to significantly shorter time to peak displacement (p = .015) and movement time (p = .003) compared to pre-tDCS trials, whereas sham stimulation had no impact on these variables.These results provide evidence that anodal tDCS applied over SMA contributes to improvements in movement kinematics of an upper limb simple RT task.Anodal tDCS over SMA could be a useful therapy to mitigate bradykinesia associated with PD.