To investigate the intervention effect of high definition transcranial alternating current stimulation(HD-tACS) in chronic post-stroke aphasia and its underlying neural mechanism by MRI.

Aphasia is one of the most frequent cognitive deficits in poststroke survivor. More than 20% of stroke patients suffered from language impairment. The recovery of language dysfunction after stroke is highly variable. Some patients recover spontaneously in the early phases of stroke, but about two thirds of patients never fully restore language ability. The purpose of this study was to explore the intervention effect of high definition transcranial alternating current stimulation in chronic post-stroke aphasia.

40 patients with language disorder diagnosed by the Aphasia Battery of Chinese (ABC) were recruited from the first affiliated Hospital of Anhui Medical University. All participants underwent a structured interview and routine laboratory examination before and after receiving HD-tACS. After meeting the inclusion criteria and obtaining informed consent, each participant will complete the clinical evaluation, functional magnetic resonance imaging (fMRI) and HD-tACS treatment conducted by trained researchers at the Neuropsychological Synergetic Innovation Center of Anhui Medical University.

All the participants were randomized (1:1) to receive "real" or "sham" treatment protocol. Stimulation electrodes were arranged in a 4 × 1 ring configuration at F1, F2, C1 ,C2 and FCz, with the central one delivering an alternating current 2 mA and the surrounding 4 electrodes delivering one-fourth of the central electrode's current in the opposite polarity. The average peak-to-peak stimulation intensity across participants was 2 mA for the 6-Hz tACS. In the sham condition, 6-Hz tACS was delivered only during the ramp-up and ramp-down periods (30 s); no current was delivered during the 30-minute intervention. The tACS stimulation lasted 30 minutes, a duration that is common in cognitive neuroscience research. During the tACS, participants sat comfortably in front of a screen, training the speech and comprehension functions to follow a speech therapist.

Before and after the HD-tACS treatment, the patients had receiving a battery measure of neuropsychological tests and Magnetic resonance imaging scan in multimodalities. Neuropsychological assessment included ABC, VFT, Token, MMSE, MoCA, HAMD, HAMA, ADL. Multimodal fMRI includes 3D-T1, rs-fMRI, DTI and ASL.

Neuropsychological evaluation and magnetic resonance imaging data were obtained again 24 hours after the last treatment. The symptoms of the patients were followed up one month after the end of treatment.

Inclusion Criteria:

• aphasia diagnosed by the ABC.
• 18-75 years old.
• native Chinese speaker.
• right-handed.
• post onset of stroke ≥6months.

Exclusion Criteria:

• mental illness .
• severe dysarthria.
• a history of head injury or surgery.
• alcohol or substance abuse.
• cerebral tumor or abscess.