The optimal site of neuromodulation for post-stroke aphasia has yet to be established. This study will investigate whether multiple sessions of cerebellar transcranial direct current stimulation (tDCS) boosts language therapy in helping people recover from aphasia as well as predict who is likely to respond to cerebellar tDCS.

Aphasia is a devastating complication of stroke. Speech and language treatment (SLT) can be helpful in restoring language function, but not all individuals show improvement. Recent studies indicate that Transcranial Direct Current Stimulation (tDCS) is a promising adjuvant approach to enhance the effectiveness of SLT. tDCS is a noninvasive, non-painful, electrical stimulation of the brain. It is believed that tDCS boosts neural plasticity that underlies recovery with SLT. A majority of the tDCS studies of aphasia have stimulated the left hemisphere regions. However, left hemisphere lesions common in post-stroke aphasia affect the electrical field in unpredictable ways, potentially preventing stimulation from reaching perilesional tissue associated with optimal recovery. The investigators' prior work addressed this problem by stimulating a novel region, the right cerebellum. The right cerebellum is connected to the left hemisphere and involved in a variety of cognitive and language functions, including naming, which is often impaired in people with aphasia. The investigators' work has shown that cerebellar tDCS is safe, easily tolerated, and improved language skills in a number of stroke participants with aphasia. The proposed project will build on these findings by conducting a randomized, double-blind, sham-controlled, trial to determine the effectiveness of cathodal tDCS to the right cerebellum for the treatment of post-stroke aphasia. The investigators will test the hypothesis that 15 sessions of cerebellar tDCS combined with an evidenced-based anomia treatment (semantic feature analysis, SFA) is associated with greater gains in accuracy in naming pictures, compared to 15 sessions of sham combined with semantic feature analysis

Inclusion Criteria:

• Chronic ischemic or hemorrhagic left hemisphere stroke
• Fluent speaker of English by self-report
• Age 18 or older
• 6 months post onset of stroke
• Diagnosis of aphasia and naming impairment using the Western Aphasia Battery-Revised

Exclusion Criteria:

• Lesion in the right cerebellum
• Previous neurological disorder (other than stroke) affecting the brain, or any other neurodegenerative disorder or psychiatric disorder
• Seizures during the previous 6 months
• Uncorrected visual loss or hearing loss by self-report
• Use of medications that lower the seizure threshold (e.g., methylphenidate)
• Use of N-methyl-D-aspartate (NMDA) antagonists (e.g., memantine)
• History of brain surgery or any metal in the head
• Severely impaired auditory comprehension (lower than 2 on the Comprehension subscore on the Western Aphasia Battery-Revised)
• Severely limited verbal output (lower than 2 on the Spontaneous Speech rating scale on the Western Aphasia Battery-Revised)
• Individuals with severe claustrophobia, cardiac pacemakers or ferromagnetic implants, and pregnant women will be excluded from the MRI portion of the study.

Upon completion of the projects and dissemination of primary study results, the analysis data files will be made available to the public, along with the final version of the study protocol, the data dictionary, and brief instructions ("read me" file). The public use data files and the accompanying documents will be made available through the National Technical Information Service (NTIS).