Joint Research Projects

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that has been proved to effectively enhance the cognitive functioning of both healthy adults and patients, for example, enhanced memory function in Alzheimer's disease, improved motor and perceptual functions of stroke patients. The current project aims to prove the effect of active-tDCS on healthy young adults; that is, whether or not it can improve and maintain the mental health of healthy participants. The experiment is divided into two conditions: Sham-tDCS and Active-tDCS. Each participant receives one stimulation condition per day and is required to complete pre-and post- flanker tasks. Since it is believed that the tDCS leads to changes in neural excitability of the brain, we hypothesize that the behavioral outcomes (i.e., accuracy and reaction time) of the flanker task would be facilitated via active-tDCS when compared with the sham-tDCS conditions. Moreover, to strengthen the reliability of the study, data are collected at both Thailand and Taiwanese sites and compared to demonstrate the potential cross-cultural difference.

Six participants (1 Male, 22-32 years, M = 26.17 ± 3.71), 3 Taiwanese, and 3 Thai, were recruited in this study. The experiment took place at 12F, NCKU hospital. Each individual needs to participate in 2 days of experiments(at least 24 hours apart). A noninvasive wireless hybrid EEG/tDCS neurostimulator device (starstim8) was applied to the participant’s head. On each experiment day, the participant needs to complete 40 trials of practice followed by a pre- flanker task, a total of 400 trials: including 200 trials of congruent condition (five arrows pointed to the same direction), and 200 trials of incongruent condition (the central arrow pointed to the different direction from the peripheral arrow), the participant was instructed to press F if the central arrow pointed to the left and press J when it pointed to the right as quickly and accurately as possible. After the pre-test, they received either Active-tDCS (offline, 1.5 mA, 20 min, Anodal electrode was placed over left-DLPFC(F3) and Cathodal electrode was placed over FP2) or Sham-tDCS (same condition as Active-tDCS with only 30 sec of stimulation), followed by a post- flanker task. The reaction time and accuracy were recorded.

Figure 1 illustrates 4 conditions of flanker stimuli used in the experiment

According to the effect of applying anodal-tDCS on the left DLPFC, we hypothesized that the active tDCS condition should facilitate one’s attention resulting in shortening RT, increasing ACC, and reducing the flanker effect, due to less distracted by the flanker. Although, our results did not illustrate the significant differences of mean RT between post-test of active and sham conditions. However, there is a trend that the mean RT of active-tDCS condition contributes to faster RT than non-stimulated (sham) condition.  It is possible that the number of participants is not sufficient to create a significant difference value. Besides, the mean ACC did not show obvious differences between each factor since the ACC of performing the flanker task was definitely high from the pre-test session. In addition, the results obtained from Taiwanese and Thai participants did not reach a significant difference between the two nationalities. Therefore, we could imply that there were no cross-cultural effects of tDCS on those participants who participated in this experiment. For future work, the number of participants should be increased to strengthen the research conclusion also the procedure should be modified such as adjusting the eletrode placement or intensity for investigating other beneficial effect tDCS.