Among the new therapeutic techniques in psychiatry, transcranial magnetic stimulation (TMS) seems to bring a profit in the treatment of depressions. It uses the principle of inductance to generate a magnetic current, which in turn activates cortical neurons. Stimulation is highly focused and interests specific regions of the cerebral cortex. This therapeutic technique is generally well tolerated. Side effects are rare, the most hampering one is epileptic seizures. It is favored by high frequencies (above 5 Hz) and arises mainly with patients having a history of personal or family epileptic seizures. The first open trials, quickly confirmed by controlled studies showed the efficiency of TMS in depression. With depression, double blind randomized trials, using high frequencies, stimulation of the left dorsolateral prefrontal cortex give positive results with significant decrease of scores on depressive scales applied to resistant and non resistant depressions. Some studies have stimulated the right dorsolateral prefrontal cortex using low frequencies. The decrease of scores is also significant on depressive scales. The modulating effect of rTMS on cortical excitability of the brain justifies this distinction between high and low frequencies, high frequencies having a facilitating effect whereas low frequencies have an inhibitory effect.
Opposite effects of high and low frequency rTMS
on regional brain activity in depressed patients
Speer AM, Kimbrell TA, Wassermann EM,
D Repella J, Willis MW, Herscovitch P, Post RM.
Biological Psychiatry Branch,
National Institute of Mental Health,
Bethesda, Maryland 20895, USA.
Biol Psychiatry 2000 Dec 15; 48(12):1133-41
BACKGROUND: High (10-20 Hz) and low frequency (1-5 Hz) repetitive transcranial magnetic stimulation (rTMS) have been explored for possible therapeutic effects in the treatment of neuropsychiatric disorders. As part of a double-blind, placebo-controlled, crossover study evaluating the antidepressant effect of daily rTMS over the left prefrontal cortex, we evaluated changes in absolute regional cerebral blood flow (rCBF) after treatment with 1- and 20-Hz rTMS. Based on preclinical data, we postulated that high frequency rTMS would increase and low frequency rTMS would decrease flow in frontal and related subcortical circuits. METHODS: Ten medication-free, adult patients with major depression (eight unipolar and two bipolar) were serially imaged using (15)O water and positron emission tomography to measure rCBF. Each patient was scanned at baseline and 72 hours after 10 daily treatments with 20-Hz rTMS and 10 daily treatments with 1 Hz rTMS given in a randomized order. TMS was administered over the left prefrontal cortex at 100% of motor threshold (MT). Significant changes in rCBF from pretreatment baseline were determined by paired t test. RESULTS: Twenty-hertz rTMS over the left prefrontal cortex was associated only with increases in rCBF. Significant increases in rCBF across the group of all 10 patients were located in the prefrontal cortex (L > R), the cingulate gyrus (L >> R), and the left amygdala, as well as bilateral insula, basal ganglia, uncus, hippocampus, parahippocampus, thalamus, and cerebellum. In contrast, 1-Hz rTMS was associated only with decreases in rCBF. Significant decreases in flow were noted in small areas of the right prefrontal cortex, left medial temporal cortex, left basal ganglia, and left amygdala. The changes in mood following the two rTMS frequencies were inversely related (r = -.78, p <.005, n = 10) such that individuals who improved with one frequency worsened with the other. CONCLUSIONS: These data indicate that 2 weeks of daily 20-Hz rTMS over the left prefrontal cortex at 100% MT induce persistent increases in rCBF in bilateral frontal, limbic, and paralimbic regions implicated in depression, whereas 1-Hz rTMS produces more circumscribed decreases (including in the left amygdala). These data demonstrate frequency-dependent, opposite effects of high and low frequency rTMS on local and distant regional brain activity that may have important implications for clinical therapeutics in various neuropsychiatric disorders.
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