Acute left prefrontal transcranial magnetic stimulation in depressed patients is associated with immediately increased activity in prefrontal cortical as well as subcortical regions.

BACKGROUND: Focal prefrontal cortex repetitive transcranial magnetic stimulation (rTMS) was originally investigated as a potential antidepressant under the assumption that in depressed patients, prefrontal cortex stimulation would produce changes in connected limbic regions involved in mood regulation.

METHODS: Fourteen adult patients with depression were scanned in a 1.5-T scanner using interleaved rTMS (1 Hz) applied on the left prefrontal cortex over 7.35 min. Images were analyzed with Statistical Parametric Mapping 2b and principal component analysis.

RESULTS: Over the left prefrontal cortex, 1-Hz TMS was associated with increased activity at the site of stimulation as well as in connected limbic regions: bilateral middle prefrontal cortex, right orbital frontal cortex, left hippocampus, mediodorsal nucleus of the thalamus, bilateral putamen, pulvinar, and insula (t = 3.85, p <.001). Significant deactivation was found in the right ventromedial frontal cortex.

CONCLUSIONS: In depressed patients, 1-Hz TMS at 100% motor threshold over the left prefrontal cortex induces activation underneath the coil, activates frontal-subcortical neuronal circuits, and decreases activity in the right ventromedial cortex. Further work is needed to understand whether these immediate changes vary as a function of TMS use parameters (intensity, frequency, location) and whether they relate to neurobiologic effects and antidepressant mechanisms of TMS.