The purpose of this study is to assess changes in language abilities of participants with chronic, post-stroke aphasia following an 8-week therapy period combined with brain stimulation. The investigators use a stimulation method called transcranial direct current stimulation (tDCS). The investigators cover two electrodes in damp sponges, place them on the scalp, and pass a weak electrical current between them. Some of this current passes through the brain and can change brain activity. One electrode is placed over language areas a bit above and in front of the left ear. The other is placed on the forehead above the right eye. Stimulation is provided twice a week for 8 weeks during aphasia therapy. The investigators believe that this stimulation may increase the effectiveness of therapy.

General Study Design: Following screening, participants complete four behavioral assessments and four brain scans (magnetic resonance imaging; MRI). Two behavioral assessments and two brain scans occur in the month before tDCS and therapy (about 3 weeks apart). One behavioral assessment and one brain scan occur in the week following therapy. The last behavioral assessment and brain scan occur approximately 8 weeks after therapy. Participants cannot receive any other speech therapy while enrolled in this study (about 20 weeks or 5 months).

Screening: Participants are screened twice, once by phone or email and once in-person at the City University of New York (CUNY). Screenings address eligibility, including adequate hearing and vision, ability to perform all required tasks, and safety for tDCS and MRI (brain scans). The investigators also collect medical and demographic information to ensure study eligibility.

Behavioral Assessment: Language samples are elicited on 11 discourse tasks, including picture descriptions, general questions, and telling a story. The Western Aphasia Battery-Revised and Boston Naming Test are also administered. These procedures are video recorded for later review and transcription. Participants also complete a pre-tDCS safety screening questionnaire. Our primary outcome measure is performance on the discourse tasks, for which the investigators measure the number of correct information units (CIUs) produced. Words are counted as correct information units if they are novel, intelligible, informative, and appropriate to the task.

Brain Scans: Brain scans (MRI) are collected at the CUNY Advanced Science Research Center (85 St. Nicholas Terrace, New York, NY 10031). Each brain scan lasts about 45 minutes. There is one task of approximately 7 minutes that will require decision-making and responses by pressing a button with the left hand. For the rest of the time, the participant simply lies still while the MRI acquires images of the brain.

Therapy: Therapy is provided for two 1-hour sessions per week for 8 weeks at the CUNY Graduate Center (365 Fifth Avenue, New York, NY 10016). This is a typical behavioral aphasia therapy intended to improve language skills. The investigators use a therapy called Verb Network Strengthening Treatment (VNeST) that has demonstrated effectiveness in a small number of research studies. tDCS (see below) is administered for the first 20 minutes of each aphasia therapy session.

tDCS: Participants undergo placement of two tDCS electrodes encased in damp sponges (saline solution). For all subjects, one electrode (anodal) is placed at the following location (EEG 10-20 system): (i) over the left inferior frontal gyrus (crossing point between T3-Fz and F7-Cz)

The other electrode (cathodal) is placed at the second site:

(ii) over right frontal pole (Fp2) Stimulation is delivered by a Soterix tDCS device for 20 minutes at an intensity of 2 milliamps (mA).

Participants are randomly assigned on an individual basis to receive either active or sham tDCS. In the sham condition, stimulation is ramped up over the first 30 seconds (as in the active condition), but then discontinued. This gives the physical perception of stimulation without the modulatory effects.

The investigators will recruit 30 total participants with aphasia for this study. There will be two parallel groups; fifteen participants will receive active tDCS and fifteen will receive sham tDCS. The investigators chose these numbers based on a preliminary trial with four participants who received aphasia treatment on the same schedule and tDCS using the same parameters. These four participants both had active and sham stimulation (crossover design) and performed much better on our primary outcome measure when they had active stimulation (i.e., produced more CIUs after active stimulation compared to before). The investigators performed a power analysis using the effect size for those four participants and determined that 30 participants will be adequate to show significant effects with two different groups.

This study recruits individuals with post-stroke aphasia as well as a group of healthy volunteers matched for age, sex, and education.

INCLUSION Criteria:

• Right handed (pre-stroke for participants with aphasia)
• High school education or equivalent
• Native English fluency without early 2nd language exposure (before age 10)
• Ability to perform the required discourse and MRI tasks (determined via in-person screening)

Additional INCLUSION Criteria for participants with APHASIA:

• Single-event left hemisphere stroke > 6 months prior to enrollment
• Aphasia diagnosis per Western Aphasia Battery-Revised
• Not receiving any other speech therapy for the entire study period (20 weeks)
• Ability to perform the required therapy tasks (determined via in-person screening)

EXCLUSION Criteria:

• Failed vision or hearing screening
• MRI contraindications (including pacemaker)
• Pregnancy
• History of seizure or change in seizure medication in past 12 months
• History of speech/language, psychiatric, or neurological disorder, or current serious medical condition (except chronic stroke comorbidities for participants with aphasia)

Additional EXCLUSION criteria for participants with APHASIA are:

• Unmodifiable hair style precluding scalp contact by electrodes
• Sensitive scalp by self-report

The investigators are committed to open, reproducible science to ensure rigor and complete transparency of our methods and data quality. Therefore, after the publication of findings, the investigators will share data with the scientific research community.

Anonymized functional magnetic resonance imaging data and associated behavioral data will be uploaded to the OpenNeuro database: https://openneuro.org/

The investigators plan to post data following conclusion of this study (anticipated 12/31/2026). The shared data will be available in perpetuity.

Data will be available on OpenNeuro database: https://openneuro.org/ Accessing data on OpenNeuro requires sign in with Google or ORCID (Open Researcher and Contributor ID; https://orcid.org/).