Theta-cordance as a biomarker of treatment response to intermittent theta burst stimulation in patients with treatment-resistant depression

• Baseline prefrontal theta cordance did not predict response to intermittent theta burst stimulation (iTBS) in depressed subjects. • Symptom improvement correlated with region-specific theta cordance change: occipital decreases, left-frontal increases. • Findings support theta cordance as a dynamic marker for monitoring iTBS effects in major depressive disorder. To test whether baseline or treatment-related changes in prefrontal theta cordance are associated with clinical outcome after intermittent theta burst stimulation (iTBS) for major depressive disorder (MDD). Retrospective analysis of 30 inpatients receiving 10 sessions of left-sided iTBS over 2 weeks. Resting-state 19-channel EEG was processed to compute theta cordance (plus delta/alpha/beta) in predefined cortical clusters pre/post the iTBS treatment period. Depression was rated pre/post with the Hamilton Depression Rating Scale (HAM-D) and the Major Depression Inventory (MDI); correlations linked baseline values and change scores to symptom improvement. Baseline prefrontal theta cordance was not associated with outcome. Change scores were region-specific: responders showed greater occipital decreases (OC p = 0.036; MLOC p = 0.009) and a trend toward left-frontal increases (MLFC p = 0.072); exploratory alpha and delta effects also emerged. Theta cordance may predict and track symptom improvement following iTBS, indicating state-dependent neurophysiology. Theta cordance may serve as a dynamic, region-specific EEG marker to monitor and personalize iTBS; prospective validation is warranted.