This clinical trial aims to explore the effect of dual-site theta-gamma cross-frequency coupled transcranial alternating current stimulation in the frontal and parietal region on the working memory ability of patients with cognitive impairment after stroke, and to evaluate the safety of this protocol. The main purpose is to answer the following question: Can dual-site cross-frequency coupled tACS in the frontal parietal region improve the performance of working memory and cognitive-motor dual tasks in stroke patients? What is its mechanism of action? Researchers will compare the effects of real cross-frequency coupled stimuli and sham stimuli to see if the real stimuli can bring better results to patients. Participants will receive 40 minutes of real or sham electrical stimulation once a day for 5 consecutive days. Clinical evaluations (cognitive scales) and fNIRS were conducted respectively before and after stimulation to record the relevant brain activities at rest and during cognitive tasks

Inclusion Criteria:

• Meeting the diagnostic criteria for hemorrhagic or ischemic stroke in the Chinese Guidelines for the Prevention and Treatment of Cerebrovascular Diseases(2nd edition), with the first onset, single hemisphere stroke, and confirmed by CT or MRI,course of diease 1-6 months;
• Age ranging from 30 to 80 years old;
• Native language is Mandarin or Cantonese;
• Right-handed;
• Diagnosed with PSCI by the MoCA scale;
• Able to cooperate in completing the speech repetition test;
• Normal hearing.

Exclusion Criteria:

• Currently receiving non-invasive brain stimulation treatment;
• Lesions involving the left DLPFC brain regions;
• History of epilepsy, mental illness,or other neurological or mental disorders;
• Any contraindications for transcranial electrical stimulation.