Antidepressant effects of different schedules of repetitive transcranial magnetic stimulation vs. clomipramine in patients with major depression: relationship to changes in cortical excitability.

The antidepressant effects of repetitive transcranial magnetic stimulation (rTMS) that have been demonstrated in recent studies could be related to its ability to modulate cortical excitability. Yet, the relationship between stimulus location and frequency and treatment outcome has not been established. The aim of the present study was to compare efficacy of rTMS in various configurations and clomipramine treatment in patients with major depression (MD) and to evaluate the relationship between clinical outcome and changes in cortical excitability. Fifty-nine MD patients were randomized to receive (1) left (n = 12) or right (n = 12) 3 Hz rTMS with placebo medication; (2) left (n = 10) or right (n = 9) 10 Hz rTMS with placebo medication; (3) active medication (clomipramine) with sham rTMS (n = 16). Both 3 Hz and 10 Hz rTMS were administered to the prefrontal cortex by a circular coil at an intensity of 110% and 100% of the resting motor threshold (rMT) respectively. Measurements of cortical excitability were performed prior to and 24 h after completion of 2 wk of daily rTMS or pharmacological treatments. These included the rMT, silent period threshold (SPT), inter-threshold difference (ITD), MEP/M-wave amplitude ratio and silent period duration (SPD). Severity of depression was blindly assessed by the Hamilton Depression Rating Scale (HDRS). The best improvement scores were seen in patients who received left 3 Hz rTMS. The 10 Hz rTMS treatment was less tolerated resulting in a significantly higher dropout rate. A significant increase of the MEP/M wave amplitude ratio accompanied by a shortening of the SPD was evidenced in patients who showed marked clinical improvement (reduction in HDRS by 50% or more) following left rTMS regardless of stimulation frequency. Our results suggest that 3 Hz left rTMS has a higher therapeutic efficacy and tolerability in patients with MD. The enhancement of cortical excitability may be related to the antidepressant action of rTMS.