Nogo-related frontal theta-band activity after magnetic seizure therapy in treatment-resistant depression: an exploratory task-based EEG study

Introduction Magnetic seizure therapy (MST) is an emerging convulsive treatment for treatment-resistant depression (TRD) with efficacy comparable to electroconvulsive therapy and superior cognitive safety. However, its neurophysiological mechanisms—particularly those underlying conflict monitoring and response inhibition—remain unclear. Frontal midline theta-band activity indexes anterior cingulate–prefrontal cognitive-control activity and may reflect inefficient neural processing in depression. Methods In this open-label, single-arm trial, 19 patients with TRD (16 female; mean age 20.89 ± 8.16 years; 10 of the 19 participants were minors) received 6–12 MST sessions using 100-Hz double-cone coil stimulation targeting bilateral F3/F4 frontal regions. Clinical assessments, including the 24-item Hamilton Depression Rating Scale (HAMD-24), Hamilton Anxiety Rating Scale (HAMA), Montgomery-Åsberg Depression Rating Scale (MADRS), and 64-channel Go/Nogo task-based electroencephalography (EEG), were performed before and after treatment. EEG outcome measures included event-related potentials (N2/P3), time-frequency power (theta/beta), microstate dynamics, and theta–beta cross-frequency coupling. Results Following MST, patients showed significant reductions in depressive symptoms (HAMD: 40.53 ± 10.25 to 22.53 ± 11.21; MADRS: 35.68 ± 8.84 to 20.68 ± 11.12). Response rates ranged from 42.1% to 57.9%. Behavioral data could not be formally analyzed due to incomplete data storage. At an uncorrected threshold, total Nogo-related theta-band activity (4–7 Hz) at Fz and FCz was lower after treatment; however, these effects did not survive FDR correction. ERP amplitudes did not change significantly. Exploratory microstate analysis showed nominal changes in Map4 AUC during Go processing and Map2 duration during Nogo processing; none survived FDR correction. These parameters should not be interpreted as reflecting changes in neural activation or inhibitory preparation. No significant changes were observed in theta–beta cross-frequency coupling or Go-condition theta power. Discussion These preliminary findings suggest that MST was associated with short-term symptom improvement and lower total Nogo-related theta-band activity at an uncorrected threshold. Because no control group, complete behavioral data, normative comparison, Time × Condition interaction, or EEG-clinical association was available, these findings cannot establish causal mechanisms, condition specificity, improved neural efficiency, or biomarker utility. Replication in adequately powered controlled studies with complete behavioral and longitudinal clinical measures is required.