Transcranial Magnetic Stimulation for the alleviation of pain

Pain is essential for all complex organisms as it minimises tissue and cellular damage, and hence prolongs survival. There are a large amount of people in the world who suffer from pain, in most cases the pain is acute, and can be managed by bed-rest and administration of analgesics such as non-steroid-anti-inflammatory drugs. The pain produced may be inconvenient, but it is incredibly important as it protects the body from any potential or further tissue damage. Pain is extremely subjective; it is thought to be shaped by interactions between expectations and incoming sensory information. It is difficult to treat because the degree of pain that is felt by each individual depends largely on their pain threshold and their sensitivity to pain. There has been extensive research into the pathology and treatment of pain.

A potential therapy for people who suffer from chronic pain is Transcranial Magnetic Stimulation. This technique has amazing prospects, as it is able to pinpoint specific areas in the cortex for stimulation, thus allowing for the manipulation of certain brain regions. TMS is a non-invasive neurostimulatory and neuromodulatory technique that was initially developed as a diagnostic tool. It has now been shown that repetitive TMS can transiently disrupt neuronal activity, and can modulate cortical excitability (either increasing or decreasing it).

During the TMS procedure, there is a stimulating (round or figure of eight) coil that is held over the subject’s head, thus, producing an electric current via electromagnetic induction. The precise mechanisms are unknown. However, it has been postulated that the electric current, depolarises the neurons causing physiological and behavioural effects depending on the area of brain that is targeted. Subsequent studies have shown that the peak discharge current needs to be several thousand amperes to depolarise the neurons in the brain.

A vast amount of studies have been carried out, using TMS to assess its affect on chronic pain. There has been profound evidence on its ability to cause short term analgesia, however scientists are dubious about the long term effects. Studies have shown that double pulse stimulation of the medial frontal cortex by TMS alleviates pain. Thus, this may be a potential stimulatory target for the relief of pain in patients suffering from chronic pain. Subsequent studies have shown that stimulation of the parietal cortex produced the greatest analgesic effect, and lessened the symptoms in subjects suffering from major depression disorders. Lefaucheur et al. showed that a single session of 10Hz TMS significantly reduced chronic pain for up to 8 days. It has been postulated that carrying out TMS on successive days may result in sustained pain relief and that TMS produces cumulative plastic changes when applied over consecutive days.

TMS seems to have promising results in some circumstances. It may be used as a future tool in alleviating chronic pain, and has been shown to have effects in individuals, who are suffering from depression, severe migraine or even autism.