• Andrew M Speer, Mark W Willis, Peter Herscovitch, Margaret Daube-Witherspoon, Jennifer Repella Shelton, Brenda E Benson, Robert M Post, and Eric M Wassermann.
• Biological Psychiatry Branch, National Institute of Mental Health, National Institutes of Health, Building 10 Room 5N234, Bethesda, MD 20892-1430, USA.
• Biol. Psychiatry. 2003 Oct 15;54(8):826-32.

BackgroundThe changes in brain activity produced by repetitive transcranial magnetic stimulation (rTMS) of the prefrontal cortex (PFC) remain unclear. We examined intensity-related changes in brain activity with positron emission tomography (PET) in normal volunteers during rTMS delivered to the left PFC.MethodsIn 10 healthy volunteers, we delivered 1-Hz rTMS at randomized intensities over left PFC with a figure-eight coil. Intensities were 80, 90, 100, 110, and 120% of the right-hand muscle twitch threshold. Regional cerebral blood flow (rCBF) scans were acquired with H(2)(15)O PET during rTMS at each intensity.ResultsRepetitive transcranial magnetic stimulation intensity was inversely correlated with rCBF in the stimulated and contralateral PFC, ipsilateral medial temporal lobe, both parahippocampi, and posterior middle temporal gyri. Positive correlations of rCBF with intensity occurred in ipsilateral anterior cingulate, cerebellum, contralateral insula, primary auditory cortex, and somatosensory face area.ConclusionsThe intensity-related inverse relationship between 1-Hz rTMS and prefrontal activity appears opposite to that seen with rTMS over the motor cortex in a companion study. Intensity-dependent increases in rCBF were seen in a number of distant cortical and subcortical areas with PFC rTMS, suggesting activation of left anterior cingulate, claustrum, and cerebellum. The regional differences in direction of rTMS effects and the greater activation of distant structures at higher intensities suggest the potential importance of higher-intensity prefrontal rTMS for therapeutic applications in neuropsychiatric patients.

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