Timing of Transcranial Direct Current Stimulation (tDCS) Combined With Speech and Language Therapy (SLT)

tDCS Implementation:

2mA of direct current for 20 minutes will be delivered using a constant current stimulator
via two electrodes in saline soaked sponges. To stimulate the left angular gyrus, a cathodal
electrode inside a saline soaked sponge (5 x 3cm) will be placed over the CP5 according to
the 10-20 international system for EEG electrode placement. The electrodes will be secured in
position by a custom-built EEG cap that will be marked with the location for angular gyrus.
The investigators will then confirm that the cathodal electrode is over the left angular
through the use of neuronavigation. The "return" anode electrode will be placed in a saline
soaked sponge (5 x 5cm) on the center of the supraorbital region.

At the beginning of the tDCS, current will slowly ram-up during the first few seconds until
it reaches 2mA. The ramp-up process will acclimate the participants to tDCS-induced
sensations (e.g., itching). At the end of the tDCS sessions, current will slowly ramp down in
the last few seconds to 0mA. The total duration of the 2mA current will be maintained for 20
minutes. For sham stimulation, the investigators will place the electrodes in the same
location as the real tDCS groups with stimulation ending after few seconds. The brief
stimulation will produce tDCS-induced sensations so that participants will not be aware when
the tDCS stopped delivering direct current

Speech-Language Treatment:

Standard-of-care treatment - script training will be used to provide SLT to our participants.
The treatment will be delivered via a computer program, Aphasia Scripts ®, whereby a virtual
therapist interactively guides the participants through treatment steps. Scripts will be five
to ten sentences and developed from common templates about topics relevant to daily life
(e.g., asking questions at the grocery store, ordering in a restaurant). The advantage of
using a computer program instead of a human therapist is that it removes extraneous variables
associated with human therapists (e.g., different levels of encouragement) and this, together
with the use of script templates, ensures treatment fidelity across participants.

Duration of an individual subject's participation in the study:

Subjects will be requested to come for baseline sessions (3 to 4 hours) before the actual
experiment. The baseline assessments may be done over two visits. In the baseline session the
subjects' aphasia severity will be assessed. The participants will also perform baseline
tasks of language and cognition in this session. Subjects will then participate in 3 weeks of
tDCS and SLT (i.e., 15 sessions). The sessions will consist of 40 minutes of SLT and 20
minutes of tDCS. Subjects will be asked to return for an assessment immediately following the
end of treatment and for follow-up testing after 4 and 8 weeks. Therefore, total number of
visits will be 19-23 sessions (depending on how many visits are needed for the assessments)
over a period of three months.

Inclusion Criteria:

- Men or women with diagnosis of fluent or non-fluent aphasia subsequent to a
left-hemisphere infarct(s) that is confirmed by a MRI or CT scan

- Aphasia quotient on the WAB of 40-80

- At least 6 months post onset of aphasia (this is beyond the stage of spontaneous
recovery)

- 18- 80 years of age

- Premorbidly fluent in English

- Premorbidly right-hand dominant per the Edinburg Handedness Inventory

- Visual acuity of 20/40 corrected

- Auditory acuity no worse than 30 dB HL on pure tone testing, aided in the better ear.

- Education greater than 12th grade

Exclusion Criteria:

- Any other neurological condition (other than cerebral vascular disease) that could
impact language and cognition such as Alzheimer's disease, Parkinson's disease,
primary progressive aphasia, and traumatic brain injury

- Active substance use

- Individuals with epilepsy