Parkinson's disease is a neurological disorder with cardinal motor signs of resting tremor, bradykinesia and lead-pipe rigidity. In addition, many patients display non-motor symptoms, including a diminished sensation of smell, gastrointestinal problems, various disorders of sleep and some cognitive impairment. These clinical features – particularly the motor signs – manifest after a progressive death of many dopaminergic neurones in the brain. Although currently available, conventional...