The goal of this study is to see if transcranial alternating current stimulation (tACS) can be used to enhance language abilities in people with post-stroke aphasia. Participants will receive real and sham tACS in conjunction with various language tests. Researchers will compare the post-stroke aphasia group with aged matched controls to see if brain response to tACS differs between groups.

This research will investigate whether transcranial alternating current stimulation (tACS), a form of noninvasive brain stimulation, can be used to enhance language abilities in people with aphasia (PWA) due to stroke and healthy older adults when compared to placebo (sham) tACS. The investigators hypothesize that alpha vs. sham tACS will improve language abilities. In addition, the investigators propose that alpha vs. sham tACS will increase local alpha power as well as alpha-induced functional connectivity, and the degree to which alpha tACS increases will be related to the degree of language performance improvement. Finally, the investigators hypothesize that PWA will exhibit abnormalities in alpha-related activity when compared to matched controls, and aphasia severity will be associated with the degree of PWA dysfunction in alpha power and alpha-driven functional connectivity.

Inclusion Criteria for Persons with Aphasia:

1. Presence of aphasia
2. Suffered a single, left hemisphere stroke
3. Stroke ≥6 months old (chronic) at the time of enrollment

Inclusion Criteria for Healthy Controls:

1. Right-handedness
2. Must be able to understand the nature of the study, and give informed consent

Exclusion criteria for Persons with Aphasia:

1. Inability to understand the nature of the study
2. Marked naming impairment
3. Impaired non-verbal, conceptual processing
4. History of significant medical or neurological disorder (other than stroke)
5. History of significant or poorly controlled psychiatric disorders
6. Current abuse of alcohol or drugs, prescription or otherwise
7. Nursing a child, pregnancy, or intent to become pregnant during the study
8. Clinically significant hearing loss
9. Contraindications to tACS
10. Contraindications to MRI

Exclusion Criteria for Healthy Controls

1. Diagnosis of a neurodegenerative disease or clinically significant cognitive complaint
2. Any unrelated neurologic or physical condition that impairs communication ability
3. History of unrelated neurological conditions including but not limited to traumatic brain injury, stroke, or small vessel disease that has resulted in a neurologic deficit
4. Any additional neurological condition that would likely reduce the safety of study participation, including central nervous system (CNS) vasculitis, intracranial tumor, intracranial aneurysm, multiple sclerosis or arteriovenous malformations
5. A medically unstable cardiopulmonary or metabolic disorder
6. Terminal illness associated with survival <12 months
7. Major active psychiatric illness that may interfere with required study procedures or treatments as determined by the enrolling physician
8. Current abuse of alcohol or drugs, prescription or otherwise
9. Contraindications to tACS
10. Contraindications to MRI