The purpose of this study is to help us understand if adding transcranial Direct Current Stimulation (tDCS), a non-invasive brain stimulation technique, to Speech Therapy improves language recovery in people with Broca's aphasia and is more effective than Speech Therapy alone.

This project is a prospective randomized controlled double-blinded clinical trial to compare auditory-visual speech therapy coupled with adjuvant active anodal tDCS (A-tDCS) versus speech therapy coupled with sham tDCS (S-tDCS). The investigators will perform an adaptive Phase II/III design, in which the first portion of the study (Phase II) will determine the optimal dose of A-tDCS (1 mA versus 2 mA) and provide a go/no-go decision for Phase III. The investigators will use a 10-10 system to determine electrode placement, with 5 x 5 cm pads, and stimulation duration will be 20 minutes. Phase III will test the definitive superiority of adjuvant A-tDCS at the optimal dose coupled with speech therapy versus speech therapy alone (S-tDCS) to improve naming among individuals with chronic Broca's aphasia.

Inclusion Criteria:

• Be willing and able to give informed consent.
• Be willing and able to comply with study requirements.
• Be between 25 and 80 years of age.
• Have used English as the primary language for > 15 years.
• Have the diagnosis of aphasia due to a left hemisphere stroke, confirmed by study physician based on past clinical MRI scan or research scan.
• Be greater than 6 months post-stroke.
• Have Broca's aphasia diagnosed by the WAB-R (fluency score ≤ 5, auditory verbal comprehension score 4-10, repetition score 0-7.9, naming and word finding score < 9).
• Correctly name 140 or fewer items on the PNT.

Exclusion Criteria:

• History of brain surgery except for during the treatment of the acute stroke.
• Seizures during the previous 12-months.
• Compromised skin at or near electrode sites (e.g., rash, eczema, wounds, infection).
• Correctly name more than 140 out of 175 items during the pre-treatment picture naming test (Philadelphia Naming Test).
• Western Aphasia Battery-Revised Aphasia Quotient (WAB-R AQ) score of 25 or below.
• Participants with open skull defects (e.g., greater than 1 cm) in the area underneath the anode electrode positioning or participants with metal implants or electrical stimulators.
• Participants with continuous oxygen therapy which cannot be discontinued for more than 1 hour.
• Any condition or situation that the PI determines would significantly interfere with the participant's ability to complete the study.