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.
