Table 2

MRS GABA levels in left DLPFC before and after TMS

OutcomeGroup; mean ± SD
Pre-rTMSPost-rTMS
Overall sample (n = 26)
GABA, IU2.0 ± 0.42.2 ± 0.4*
 Grey matter, % volume46.8 ± 5.548.4 ± 5.6
 White matter, % volume36.0 ± 8.333.5 ± 8.9
 CSF, % volume16.8 ± 4.917.7 ± 5.6
TMS responders (n = 12)
 GABA, IU1.9 ± 0.42.3 ± 0.3*
 Grey matter, % volume48.3 ± 5.050.1 ± 5.1
 White matter, % volume32.9 ± 6.029.5 ± 6.0
 CSF, % volume17.9 ± 3.219.8 ± 4.4
TMS nonresponders (n = 14)
 GABA, IU2.0 ± 0.42.1 ± 0.4
 Grey matter, % volume45.5 ± 5.847.0 ± 5.8
 White matter, % volume38.5 ± 9.236.9 ± 9.8
 CSF, % volume15.9 ± 5.915.9 ± 6.0
  • CSF = cerebrospinal fluid; DLPFC = dorsolateral prefrontal cortex (middle frontal cortex); GABA = γ-aminobutyric acid; IU = institutional units; MRS = magnetic resonance spectroscopy; rTMS = repetitive transcranial magnetic stimulation; SD = standard deviation.

  • * p < 0.05: repeated-measures analysis of variance (accounting for use of GABAergic medication and TMS stimulation hemisphere) for overall sample, or post hoc protected t test of the a priori hypothesis of post-TMS GABA elevation for the TMS responder subsample.

  • Responder status based on ≥30% reduction in the 30-item Inventory of Depressive Symptoms score after rTMS treatment.30