Aphasia is a debilitating disorder, typically resulting from damage to the left
hemisphere, that can impair a range of communication abilities, including language
production and comprehension, reading, and writing. Approximately 180,000 new cases of
aphasia are identified per year, and approximately 1 million or 1 in 250 are living with
aphasia in the United States (NIH-NIDCD, 2015). Treatments are limited and provide modest
benefits at best. The current emphasis in aphasia rehabilitation is to formulate
intensive speech and language therapies and augment therapeutic benefits by providing
brain stimulation concurrent with therapies.
The current study will investigate the efficacy of high-definition tACS (HD-tACS) to help
restore neural oscillatory activity in aphasia. TACS differs from widely used
transcranial direct current stimulation (tDCS) in that sinusoidal, alternating currents
are delivered rather than constant currents. TACS can manipulate the ongoing oscillatory
neuronal activity and potentially increase functional synchronization (or connectivity)
between targeted areas. This feature of tACS is quite attractive, given the new body of
evidence suggesting that language impairments stem from diminished functional
connectivity and disruptions in the language network due to stroke. The selection of tACS
frequencies in this study is guided by our preliminary work examining pathological neural
oscillations found near stroke-lesioned areas (or perilesional) in aphasia and by the
involvement of specific frequencies during a verbal short-term memory task. By
exogenously tuning the neural oscillations with tACS, the investigators hope to
up-regulate communication across regions within the language network and other connected
areas to improve outcomes. If successful, tACS will be a powerful and novel treatment
approach with reverberating positive impact on long-term recovery.
The study will employ HD-tACS in a within-subject and sham-controlled design, using
frequencies ranging from theta to low-gamma (4-40 Hz) combined with language tasks.
Magnetoencephalography (MEG) or electroencephalography (EEG) will be used to determine
tACS frequencies and to evaluate behavioral and neurophysiological changes in response to
tACS. Investigators plan to recruit 200 participants: 100 stroke survivors with aphasia
and 100 healthy controls.
Participants will complete language testing that covers a broad range of language
functions, medical history, and MRI. Eligible participants will undergo active tACS or
sham-tACS over 3-4 sessions. The tACS administrator and participants will be blinded to
the stimulation type. The order of stimulation type will be counterbalanced across
participants. Washout period between visits will be at least 48 hours to minimize
potential carryover effects. MEG will be collected prior to tACS sessions during a
language task to determine tACS frequency. EEG may be acquired before and after tACS
during periods of rest (resting-state) and during language tasks. Participants will
complete a questionnaire at the end of stimulation visits to assess potential side
effects of tACS. Total time enrolled in the study is expected to be 2-3 weeks, which may
be longer depending on participant's availability.
