Tehran University of Medical Sciences Journal of Sleep Sciences 2476-2938 7 3-4 2024 03 03 80 89 Tahereh Motevalizadeh Department of Psychology, School of Literature and Humanities, Lorestan University, Khorramabad, Iran Fatemeh Rezaei Department of Psychology, School of Literature and Humanities, Lorestan University, Khorramabad, Iran Khosro Sadeghniiat Haghighi Sleep Breathing Disorders Research Center, Tehran University of Medical Sciences, Tehran, Iran; Occupational Sleep Research Center, Baharloo Hospital, Tehran University of Medical Sciences, Tehran, Iran Mohammad Ali Sepahvand Department of Psychology, School of Literature and Humanities, Lorestan University, Khorramabad, Iran 2023 06 26 2023 09 03 Background and Objective: Insomnia is the most common sleep problem which is associated with cortical over-excitation. Transcranial direct-current stimulation (tDCS) potentially modifies insomnia-related cortical state. There-fore, we tested the hypothesis that insomnia severity can be modulated by tDCS. Materials and Methods: The current study was conducted with a pretest-posttest design and a control group. A total of 32 women with insomnia were randomly categorized into an intervention group (active stimulation) and a control group (sham stimulation). In the intervention group, tDCS was used with an intensity of 2mA for 20 to 30 minutes during 12 sessions (3 times a week). Anodal stimulation was performed on the left primary motor cortex (M1) and cathodal stimulation was performed on the right dorsal lateral prefrontal cortex (DLPFC). The control group received sham stim-ulation for 20 to 30 minutes during 12 sessions (3 times a week). All participants were evaluated before and after the intervention using the Insomnia Severity Index (ISI) and Positive Affect and Negative Affect Schedule (PANAS). Results: The results of univariate analysis of covariance (ANCOVA) and multivariate analysis of covariance (MANCOVA) showed a significant difference between the tDCS group and the sham group in terms of reduction in the severity of insomnia. We also observed that positive affect increased and negative affect decreased following insomnia treatment (P ≤ 0.005). Conclusion: The results of our study indicated that performing our designed tDCS protocol for treating insomnia can be effective in treating insomnia and improving positive and negative affect. https://jss.tums.ac.ir/index.php/jss/article/view/261