Vagus nerve stimulation (VNS) is thought to activate neural pathways that release chemicals which promote plasticity and learning. Previous work has shown that the auricular branch of the vagus nerve innervates landmarks on the external ear. Work from the PI's laboratory has shown that electrical current applied to the external ear modulates physiological indexes of brain states implicated in the therapeutic effects of VNS. The broad objective of this project is to better understand physiological mechanisms modulated by auricular stimulation to support possible therapeutic effects in the form of motor learning.

Existing evidence supports the use of VNS to enhance the effects of traditional therapy on impairments due to neurological injury. It is known that the vagus nerve forms contacts with neuromodulatory nuclei in the brainstem that release of chemicals shown to be critically involved in attentional control and memory formation. It is also known that the auricular branch of the vagus nerve innervates portions of the external ear providing a possible means to engage similar neural pathways noninvasively via transcutaneous auricular vagus nerve stimulation (taVNS). Recent work from the PI's laboratory shows that electrical current applied to landmarks on the external ear elicits transient effects on pupil dilation, an established physiological index of brain states that support learning. Given the ability to engage the biomarker, the investigators aim to further investigate physiological mechanisms modulated by taVNS and possible effects on learning.

Inclusion Criteria:

ALL PROSPECTIVE SUBJECTS:

1. 18-75 years of age

   PROSPECTIVE SUBJECTS DIAGNOSED WITH STROKE:

2. Diagnosis of a single stroke resulting in hand impairment

3. Diagnosis of stroke at least six months prior to the time of participation

Exclusion Criteria:

ALL PROSPECTIVE SUBJECTS:

1. History of vestibular disorders or dizziness

2. Difficulty maintaining alertness and/or remaining still

3. Pregnant or expecting to become pregnant

4. Diagnosis of neurological and/or musculoskeletal disorder(s) (other than stroke) that affect movement

5. Ocular disease and/or impairment in more than one eye

6. History of seizure and/or epilepsy

7. Implants, devices, or foreign objects in the brain/body that are incompatible with MRI

8. Body size that is incompatible with MRI scanner dimensions

9. Anyone already enrolled and actively participating in another greater than minimal risk study.

   PROSPECTIVE SUBJECTS DIAGNOSED WITH STROKE:

10. Other impairments secondary to stroke (e.g., attention, cognition, etc.) that would interfere with the ability to understand study goals or follow simple instructions, as judged by the investigators.