Study to Investigate Vagus Nerve Stimulation to Augment Executive Function in Healthy and Cognitively Impaired Populations

This study is testing whether gentle electrical stimulation of the vagus nerve — delivered through the ear — can improve thinking, memory, and mental focus in healthy adults and people with Parkinson's disease. The vagus nerve connects the brain to many parts of the body and plays a role in brain function. **You may be eligible if...** - You are between 18 and 65 years old - You are able to follow written and spoken instructions - If you have Parkinson's disease: you have been clinically diagnosed and do not have severe motor or thinking problems **You may NOT be eligible if...** - You have an uncontrolled or serious medical condition - You have an ear infection or abnormal ear anatomy - You have an electronic implant such as a pacemaker or cochlear implant - You have uncorrected vision problems that would interfere with the tasks - You have other significant diseases that might affect participation Talk to your doctor to see if this trial is right for you.