Health Adults

Due to the difficulties and risks of directly measuring prenatal hormone levels, biomarkers that indirectly reflect this exposure are used in research. In this context, the ratio of second to fourth finger length (2D:4D) is widely preferred because it is an easily applicable and non-invasive measurement. Evidence shows that 2D:4D stabilizes from the second trimester of pregnancy onward and exhibits strong sex differences across populations. The 2D:4D ratio is generally lower in men than in women. 2D is more strongly influenced by prenatal estrogen, while 4D is more strongly influenced by prenatal testosterone; this occurs during the first trimester of intrauterine fetal development. To our knowledge, studies examining the relationship between the 2D:4D ratio, an indirect indicator of prenatal androgen exposure, and dexterity and tactile discrimination are limited. Accordingly, the planned study aims to evaluate the relationship between the 2D:4D ratio and fine motor skills and tactile discrimination in healthy young adults.

The goal of this clinical trial is to validate if temporal interference brain stimulation (TIBS) is safe in healthy volunteers aged 20 to 65. The main questions it aims to answer are: * Is it safe to apply TIBS intervention to the left hippocampus in healthy participants? * Is it safe to apply TIBS intervention to the left insula in healthy participants? * Is it safe to apply TIBS intervention to the left anterior cingulate cortex in healthy participants? * Is it safe to apply TIBS intervention to the right inferior frontal cortex in healthy participants? Participants will: * Be Randomly allocated to either sham-first group or treat first-group, stratified by stimulated brain region, following a crossover-controlled experimental design * Complete baseline cognitive evaluations and mental status assessments, and undergo a baseline MRI scan on the same day * Receive stimulation for 5 consecutive days, followed by a 2-days washout period, then complete the remaining 5 days of stimulation. * Complete post-intervention cognitive evaluations and mental status assessments, and undergo a post-intervention MRI scan on the same day