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Transcranial magnetic stimulation (TMS) is a relatively recent technique for both the treatment of cognitive disorders such as depression or auditory hallucinations, and for brain research. It works by using an inductive magnetic field, similar to a metal detector but significantly more powerful, to excite neurons electrically.
The first successful TMS study was carried out in 1985, making the field relatively recent within medical science. It looks promising as an alternative to the much more invasive electroconvulsive therapy. It is capable of being targeted with a precision of several millimeters, and is designed only to research the very surface of the brain - the cortex. Because many cognitive functions are located in the cortex, however, this is not a serious limitation.
Research is ongoing and the scientific community has high hopes for TMS, with preliminary experiments even suggesting that it could be used one day to build a machine that quickly induces REM sleep, giving the rejuvenating equivalent of a full night's sleep in only two or three hours. Double-blind studies have also proven that it is effective in the treatment of depression and migraines.
As of May 2007, over 3,000 studies on TMS have been published, with positive therapeutic results ranging from treatments of post-traumatic stress syndrome to tinnitus (a persistent ringing in the ears). Applications of this therapy to the visual cortex can produce phosphenes on demand. Phosphenes are the little blurs of colored light you see when you rub your eyes.
There are two primary types of TMS - single or paired pulse, and repetitive TMS (rTMS). RTMS involves multiple sessions over days or weeks, and is distinct in that it can induce long-term changes to the brain. Single pulse TMS only works while the magnetic field is being applied, limiting its use for therapy but providing an intriguing research tool. Selective TMS applications have been found to temporarily increase artistic ability in some patients, similar to cases involving autistic-savants. As such, this technique is sometimes marketed as a "savant on demand" technology and may have applications in intelligence enhancement, though much more careful research is required to investigate this.
One of the main limitations in wider deployment and further research involving TMS is that the technology is relatively costly. Numerous capacitor banks are required to store and release the necessary energy to apply the tool effectively. Most systems cost between $25,000 and $100,000 US Dollars, although there are "open TMS" projects working to build systems for less than $1,000 USD, within the budget of the hobbyist or independent experimenter.