Methods:We conducted a secondary analysis of 64 patients across three sites implementing FDA-cleared TMS protocols for treating depression: daily 10-Hz (n = 40) and accelerated-iTBS (n = 24).TMS-induced E-Fields were computed with MRI-based FEM models at the motor cortex (M1) and treatment target in the prefrontal cortex (PFC).Two metrics were calculated for each subject: PFC E-Field strength (V/m) and effective %rMT (percentage of M1-E-Field delivered to PFC).Clinical improvement was defined as percent reduction in depression score (PHQ-9 or BDI) from baseline to end-of-treatment.Relationships were analyzed using robust linear regression controlling for site, age, sex, and baseline severity.Results: Both metrics showed negative relationships with clinical improvement.PFC E-Field strength exhibited a consistent directional trend ( = -0.617,p = 0.114).Higher effective %rMT, which accounted for individual differences in cortical excitability, was significantly and inversely correlated with symptom improvement ( = -0.487,p = 0.009).Discussion: Lower relative stimulation intensities were associated with better clinical outcomes across protocols for depression.These retrospective findings warrant systematic investigation of TMS parameters in larger randomized trials.
Johnson et al. (Mon,) studied this question.