This study plans to learn more about how stimulating the vagus nerve through gentle electrical stimulation applied to the ear can affect decision-making, problem-solving, and other thinking abilities. This process, called transcutaneous auricular vagus nerve stimulation (taVNS), could help improve brain function in both healthy individuals and people with Parkinson's disease (PD).

This is a single-site pilot study to assess the safety, feasibility, and potential therapeutic effect of paired-taVNS cognitive training in healthy individuals and people with PD. In the longitudinal study, healthy and PD participants will be prospectively assigned to receive either the sham or active intervention based on order of enrollment in the study. In the acute study, healthy participants will receive both the sham and active intervention, where the order will be prospectively randomized based on order of enrollment in the study.

Inclusion Criteria:

1. Individuals aged 18-65.
2. Ability to sign informed consent.
3. Ability to follow written and verbal instructions.
4. For the PD group, a clinical diagnosis of Parkinson's disease without severe motor or cognitive impairments.

Exclusion Criteria:

1. Current uncontrolled and/or clinically significant medical condition.
2. Abnormal ear anatomy or active ear infection.
3. Electronic medical implants, such as pacemakers, cochlear prosthesis, neuro-stimulators.
4. Uncorrected visual impairments that would interfere with task performance.

(6) Other significant diseases or disorders that might impair study participation.