en Cognitive Neuroscience Cognitive Neuroscience Original Original <div style="text-align: justify;"><span style="font-size:14px;"><span style="font-family:Tahoma;"><span style="line-height:2;"><b>Purpose:</b> This exploratory, proof-of-concept study investigated whether prefrontal theta cordance could serve as a candidate early indicator of response to anodal transcranial direct current stimulation (atDCS) in treatment-resistant depression (TRD), focusing on a homogeneous sample of young adult females. All findings are strictly hypothesis-generating and require external validation.<br> <strong>Method:</strong> Thirty female TRD patients were assessed using the Beck Depression Inventory-II (BDI-II) and resting-state EEG at baseline, after seven atDCS sessions (week 1), and after 14 sessions (week 2). Early response was defined as a 30% or greater reduction in BDI-II scores at week 1. Theta cordance was computed for the prefrontal (PF), midline left frontal (MLF), and midline right frontal (MRF) regions.<br> <b>Results:</b> Significant reductions in theta cordance were observed in the PF and MLF regions at week 1, with MLF changes showing a very large effect size (Cohen&rsquo;s <i>d</i> = 4.77) and robust group differentiation. This effect size is likely sample-specific and unstable. Exploratory logistic models combining week-one symptom improvement (&Delta;BDI) with changes in cordance were significant. The &Delta;BDI+&Delta;MLF model showed the strongest within-sample association with the outcome (AUC = .897). However, this estimate is likely inflated due to the small sample (<i>N</i> = 30) and the absence of internal validation (e.g., cross-validation); it should be interpreted as a preliminary, hypothesis-generating finding only.<br> <b>Conclusion:</b> Preliminary results suggest that early MLF theta cordance reduction is a prominent electrophysiological correlate of concurrent clinical improvement in this specific cohort of young adult females with TRD. These associative findings are strictly preliminary and demographic-specific. They underscore a need for validation in larger, sham-controlled trials with prospective designs before any consideration of clinical translation.</span></span></span></div> Brain Stimulation, Electroencephalography, Theta cordance, Treatment-Resistant Depression  0 0 http://bcn.iums.ac.ir/browse.php?a_code=A-10-2935-3&slc_lang=en&sid=1 Seyed Ruhollah Hisseini r_hosseini@um.ac.ir 13700319475328460058247 13700319475328460058247 Yes Department of Psychology, Faculty of Education and Psychology, Ferdowsi University of Mashhad, Mashhad, Iran. Roghieh Nooripour nooripour@iau.ir 13700319475328460058248 13700319475328460058248 No Department of Counseling, Qa.C., Islamic Azad University, Qazvin, Iran Nikzad Ghanbari nik.gh.pirkashan@gmail.com 13700319475328460058249 13700319475328460058249 No Department of Clinical Psychology, Faculty of Psychology and Educational Sciences, Shahid Beheshti University, Tehran, Iran Abbas Firoozabadi a.firoozabadi@um.ac.ir 13700319475328460058250 13700319475328460058250 No Department of Psychology, Faculty of Education and Psychology, Ferdowsi University of Mashhad, Mashhad, Iran.