Study reveals link between changes of neuronal activities and dyskinesia Many people with Parkinson's disease develop abnormal movements called L-DOPA induced dyskinesia, a major side effect of long-term medication. The mechanism underlying this side effect has been unknown. In this study, researchers have revealed relation between changes of neuronal activities and dyskinesia. Parkinson's disease (PD) is the common age-related neurological disorder affecting 7 - 10 million people worldwide. It is caused by loss of dopaminergic neurons in the brain region called the substantia nigra, and induces difficulty in execution of movements (akinesia), muscle stiffness (rigidity), walking difficulty, tremorous hand movements (tremor), and non-motor symptoms such as depression and sleep disturbance.