The Antidepressive Effect of Low Frequency Right Prefrontal Repetitive Transcranial Magnetic Stimulation as add-on to Antidepressant Drug Treatment. A Blinded, Placebo Controlled Randomised Study.

rTMS has appeared a potential new non-invasive antidepressant method, which implies non-convulsive focal stimulation of the brain through a time varying magnetic field. ). RTMS is based on the principle of electromagnetism. An electromagnetic coil placed on the scalp produces a time-varying magnetic field that penetrates the scalp and skull unattenuated and gives rise to a current in the proximity of the cerebral cortex as well as functionally connected parts of the brain. Research on rTMS reports of minimal side effects of the method Previous research indicates that the antidepressant effect of rTMS is associated with specific stimulation of the dorsolateral prefrontal cortex. The stimulus frequency has shown to play a key role in the mechanisms of action of rTMS. Previous animal studies have shown that low frequency rTMS is associated with long term inhibition of neuronal activity (long term depression), while high frequency stimulation is followed by prolonged activation (long term potentiation). To some extent, this differential effect of different frequencies is reflected in human studies (REF).

The majority of clinically controlled studies have used high frequency stimulation of the left frontal cortex , which has been approved by the USA FDA (1) and later in EU for the treatment of depression.

Fewer studies have used right prefrontal, which has less side effects, such as local discomfort and a lower risk of releasing epileptic seizures, than high frequency stimulation . In addition low frequency rTMS is generally less time-consuming. Both stimulus models has been shown to have a modest, statistically significant antidepressant effect and recent research clearly indicates that low frequency rTMS of the right prefrontal cortex i associated with an antidepressant effect at the same level as the high frequency model. The issue indicates that low frequency due to the more advantagous side effect profile should be the stimulus model of choice in a clinical setting.

Therefore the investigators want to examine the antidepressant effect of a specific rTMS low frequency model in a clinical setting using a placebo controlled, randomized double blind design.