Tehran University of Medical Sciences Journal of Sleep Sciences 2476-2938 8 3-4 2026 07 25 53 59 Hamid Reza Dehghan Department of Psychology, School of Literature and Humanities, Shahid Bahonar University of Kerman, Kerman, Iran Sayyed Mohammad Hossein Mousavi Nasab Department of Psychology, School of Literature and Humanities, Shahid Bahonar University of Kerman, Kerman, Iran Mahshid Tajrobehkar Department of Psychology, School of Literature and Humanities, Shahid Bahonar University of Kerman, Kerman, Iran 2024 01 15 2024 11 09 Background and Objective: This study aimed to investigate the effects of transcranial direct current stimulation (tDCS) on processing speed, life satisfaction, and emotional states in students with poor sleep quality. Materials and Methods: A semi-experimental pretest-posttest design with a control group was applied. Twenty-seven students with poor sleep quality were selected via convenience sampling. The Pittsburgh Sleep Quality Index (PSQI), the Reaction Time Index (RTI) task from the Cambridge Neuropsychological Test Automated Battery (CANTAB), the Symbol Digit Modalities Test (SDMT), the Satisfaction with Life Scale (SWLS), and Depression, Anxiety, and Stress Scale-21 (DASS-21) were used to collect data. After the pretest, participants were randomly assigned to the intervention (n = 14) or control group (n = 13). The intervention comprised ten 20-minute tDCS sessions at two mA, with the anode over F3 and the cathode over F4. Data were analyzed via analysis of covariance (ANCOVA). Results: After controlling for pretest scores, the intervention and control groups demonstrated a significant difference in posttest processing speed (computer-based and non-computer-based tests) and the anxiety subscale of the negative emotional states . No significant differences were found regarding sleep quality or life satisfaction. Conclusion: tDCS improved processing speed and reduced negative emotional states, but did not significantly improve sleep quality or life satisfaction. https://jss.tums.ac.ir/index.php/jss/article/view/283