Effect of two weeks of rTMS on brain activity in healthy subjects during an n-back task: a randomized double blind study.

Background: Repetitive transcranial magnetic stimulation (rTMS) has shown significant efficiency in the treatment of several psychiatric disorders. In depressive disorders, the dorsolateral prefrontal cortex (DLPFC) is the main target for rTMS, but the effects of this stimulation on cognitive functions and their neural correlates are not well known. Previous works have established that the left DLPFC is reliably activated during the n-back working memory task.

Objective: The aim of this randomized double-blind study was to determine the impact of rTMS applied to the DLPFC on brain activity during an n-back task in healthy subjects.

Methods: After randomization, twenty subjects received either active treatment (10 sessions; 1 session a day; frequency = 10 Hz; intensity = 110% of motor threshold) or placebo treatment (sham coil). Subjects performed an n-back task during two functional magnetic resonance imaging sessions (one before stimulation, and one after 10 active or sham rTMS sessions).

Results: No significant changes, neither in mood nor in performance in the n-back task, were shown. A significant group-by-time interaction effect was found in the bilateral middle frontal gyrus and in the left caudate nucleus.

Conclusions: These results show that rTMS applied on the left DLPFC had close and remote effects on brain areas involved in working memory.