tACS applied to the MFC at a frequency of 6 Hz, using a high-definition 1×4 electrode configuration with individualized current intensity, delivered for 20 minutes.

The VFT assesses abilities such as thought initiation, rapid word retrieval, and cognitive flexibility. It has two parts: 1.Phonemic Fluency Test (PFT), people needed to name as many Chinese words as possible beginning with "fa" or "xiao" within 60 seconds. 2.Semantic Fluency Test (SFT), people needed to name as many items as possible from categories such as "fruits," "vegetables," "animals," and "occupations" within 60 seconds. The number of correct and non-repeated words produced within the time limit were recorded.

The DST assesses working memory and selective attention. People repeat a series of numbers in the same order (forward) or reverse order (backward) as spoken by the examiner. The maximum correctly repeated sequence length was recorded.

The TMT assesses complex visual scanning, conceptual tracking, cognitive flexibility and divided attention. It has two parts: TMT-A: People draw a trail by connecting 25 Arabic numbers in ascending order. TMT-B: the trail alternates between connecting 12 Arabic numbers and 12 Chinese characters. The time taken to complete each task is recorded.

In the FAF task, participants needed to sit in a sound-attenuated room and produce the vowel /u/ according to instructions. The acoustic signal is recorded and randomly shifted in pitch by an external device. The pitch-shifted voice is then fed back to the participant. This unexpected pitch perturbation elicits either an opposite or a following acoustic compensation response. The amplitude and timing of this response are recorded and used to assess the participant's speech-motor integration ability.

During the FAF task, cortical electrical activity associated with the pitch perturbation event was simultaneously recorded. Using the perturbation onset as the zero point, a time window ranging from -500ms to 700ms was defined. The peak amplitude and latency of N1 and P2 components were extracted within 80-180 ms and 160-280 ms time windows after the perturbation onset, respectively.