Transcranial Magnetic Stimulation has increasingly been used as a treatment for mental illnesses like major depression. High frequency rTMS targeted to the left dorsolateral prefrontal cortex has mood elevating effects on patients. When this high frequency is used, the brain area being stimulated actually becomes more active. People with depression often have underactivity in this area of the brain and this leads to feelings of apathy and lethargy. Recently a new meta-analysis of studies has come out indicating that this treatment does in fact work better than sham treatment.

The researchers looked at thirty double-blind sham-controlled parallel studies that had a total of 1164 patients and found that the real treatment was clinically significantly more effective than sham treatment. The effect on mood was similar in size to commercially available antidepressants.

Researchers have actually had quite a bit of difficulty in distinguishing real rTMS from placebo or sham rTMS for several different trials. Depression is a multifaceted disorder. It has many different symptoms and simulation of the left dorsolateral prefrontal cortex might only be expected to improve specific symtpoms. Many other symptoms might not improve when stimulating that area. The benefits to rTMS is that stimulating the left dorsolateral prefrontal cortex with transcranial magnetic stimulation is relatively selective and has few if any side effects. Stimulating that area of the brain could be expected to improve apathy, anergia, indifference, poor concentration and also psychomotor retardation(slowed speaking).

Researchers have also found that if they use low frequency stimulation targeted to another area of the brain (the right dorsolateral prefrontal cortex) they can also improve a person's mood. In this area they use TMS to reduce overactivity as opposed to increasing it. Recently researchers have found a way to get even more of a response from the low frequency TMS by doing something called "priming". This is basically using a higher frequency to stimulate the target area and then following it by stimulation with a lower frequency. Low frequency stimulation has the benefit of not causing a seizure unlike high frequency. So researchers may be more likely to decrease brain activity with low frequency rTMS.

I think in the future doctors will be able to look at a brain scan to tell which areas are overactive or underactive in comparison to a real brain. Then they will be able to use TMS to selectively increase or decrease activity in specific brain regions. This will allow a very targeted treatment for many brain based disorders. A person can have their treatment very targeted to improve their specific symptoms.