Transcranial Alternating Current Stimulation (tACS) for the Recovery of Phonological Short-Term Memory in Patients With Aphasia After Stroke

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. 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, potentially with 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 stroke survivors with aphasia. TACS differs from trancranial direct current stimulation (tDCS), a widely used brain stimulation paradigm, in that sinusoidal or alternating currents are delivered rather than direct currents. TACS is shown to manipulate ongoing oscillatory brain activity and also to modulate synchronization (or connectivity) between targeted brain areas. This feature of tACS is quite attractive, given the new body of evidence suggesting that language impairments stem from diminished brain connectivity and ensuing disruptions in the language network due to stroke.

The study will employ high-definition tACS (HD-tACS) in a parallel, double-blinded, sham-controlled design combined with language therapy targeting phonological short-term memory (STM) function in stroke survivors with aphasia. Magnetoencephalography (MEG) and fMRI BOLD data collection will occur to determine tACS parameters and to evaluate stimulation-induced neural changes, respectively. The investigators plan to recruit 120 stroke survivors with aphasia in a 2-group tACS study design.

Inclusion criteria

• Diagnosed with left hemisphere stroke/aphasia
• Consent date >= 1 month after stroke onset
• Fluent in English
• 18 years of age or older

Exclusion criteria

• Severe cognitive, auditory or visual impairments that would preclude cognitive and language testing
• Presence of major untreated or unstable psychiatric disease
• A chronic medical condition that is not treated or is unstable
• The presence of cardiac stimulators or pacemakers
• Contraindications to MRI or tACS, e.g. patients with metallic implants, and/or history of skull fractures, pregnancy, skin diseases
• History of ongoing or unmanaged seizures
• History of dyslexia or other developmental learning disabilities