Could a zap on the forehead ease Parkinson's shuffling?

This study tests whether a non-invasive device that gently stimulates a nerve on the forehead (external trigeminal nerve stimulation, or eTNS) can immediately improve walking and other movement problems in people with Parkinson's disease. Thirty participants will each try two different stimulation frequencies and a sham (fake) session in random order, all while on their regular medication. The goal is to see if eTNS can reduce the difficulty of walking while doing another task, like talking.