Abstract
BACKGROUND: Studies have demonstrated that both transcranial direct current stimulation (tDCS) and caffeine improve cognitive abilities through similar mechanisms. This study investigated the acute effects of tDCS combined with caffeine on executive functions. METHODS: Eighty females were randomly assigned to four groups (tDCS + caffeine, tDCS + placebo, sham tDCS + caffeine, and sham tDCS + placebo). Each participant completed two experimental sessions. In the first session, participants performed the Stroop, 3-back, and More-Odd Shifting tasks (T0). For the second session, participants ingested a 200 mg caffeine capsule/placebo, waited 45 minutes, and then received 2 mA real or sham tDCS for 20 minutes. Next, they performed the same cognitive tasks as in the first session (T1), and rested for 30 minutes before completing the cognitive test again (T2). RESULTS: Accuracy in the 3-back task was significantly improved for the tDCS + caffeine group at T1 and T2, for the tDCS + placebo group at T1, and for the sham tDCS + caffeine group at T2 compared to the sham tDCS + placebo group. Accuracy on the Stroop task was significantly enhanced in the tDCS + caffeine group at T1 compared to the sham tDCS + caffeine and sham tDCS + placebo groups, and in the tDCS + placebo group at T1 compared to the sham tDCS + caffeine group. No significant differences were observed among groups for the More-Odd Shifting task. CONCLUSIONS: These findings suggest that both tDCS and caffeine interventions can improve cognitive task performance, and their combination results in more persistent improvements in executive functions compared to tDCS or caffeine alone.