Participants with Major Depressive Disorder(MDD) receive active Electroconvulsive Therapy (ECT) according to the study protocol, in addition to their ongoing standardized pharmacotherapy. This group assesses the efficacy and cognitive effects of ECT.

Participants with Major Depressive Disorder (MDD) receive active Magnetic Seizure Therapy (MST) according to the study protocol, in addition to their ongoing standardized pharmacotherapy. This group assesses the efficacy and cognitive effects of MST, allowing for comparison with ECT.

Healthy volunteers with no history of major neuropsychiatric disorders. They do not receive any neuromodulation intervention (ECT or MST) or study-related pharmacotherapy. They undergo the same cognitive and behavioral assessments at matched time points to provide normative baseline data for comparison.

Electroconvulsive therapy will be administered two to four times a week according to a standardized protocol. Stimulation parameters (including intensity, target location, session number, and duration) will be individualized for each participant based on prior research to ensure targeted and safe delivery within established safety limits. Treatment will continue until the participant meets the protocol-defined response criteria or completes a maximum of 10 sessions.

The Hamilton Depression Rating Scale is a clinician-administered scale used to assess the severity of depressive symptoms. The 17-item version (HAMD-17) is most common. Each item is rated on a 3- or 5-point scale. The total score ranges from 0 to 52, with a higher score indicating more severe depression. The primary endpoint is the change in total score from baseline.

ECG recordings will be analyzed to assess changes in heart rate variability (HRV) as a potential biomarker of autonomic nervous system function in response to treatment. Key parameters include the root mean square of successive differences (RMSSD) and the standard deviation of NN intervals (SDNN).

The HAMA is a 14-item clinician-rated scale assessing anxiety severity. Total score ranges from 0 to 56, with higher scores indicating worse anxiety. The change from baseline to the end of treatment will be the primary measure of clinical efficacy.

The MCCB is a standardized, performance-based cognitive battery used to assess global cognitive functioning. The primary measure is the change in the Overall Composite T-score (derived from 10 tests across 7 domains), with higher scores indicating better cognitive performance. Assessments are administered by trained personnel.

This will be assessed by measuring changes in functional connectivity (FC) OR the amplitude of low-frequency fluctuations (ALFF) within specific brain regions.