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While several treatments based on the use of magnetic fields have been reported in peer-reviewed journals, the only ones that have been approved by the FDA are the use of pulsed magnetic fields to aid non-union bone fractures. Transcranial magnetic stimulation is currently under active study in multiple research centres, and will likely become an approved therapy in the future.
Bioelectromagnetics is not to be confused with bioelectromagnetism, which deals with the ability of life to produce its own electromagnetism.
Additional recommended knowledge
Introduction: general features of observed interactions
Thermal vs nonthermal nature
Most of the molecules that make up the human body interact only weakly with electromagnetic fields (EMF) that are in the radiofrequency or extremely low frequency bands. One basic interaction is the absorption of energy from the EMF, which can cause tissue to heat up; more intense field exposures will produce greater heating. This heat deposition can lead to biological effects ranging from discomfort to protein denaturation to burns. Many nations and regulatory bodies (for example, the International Commission on Non-Ionizing Radiation Protection) have established safety guidelines to limit the EMF exposure to a non-thermal level, which can either be defined as heating only to the point where the excess heat can be dissipated/radiated away, or as some small temperature increase that is not detectable with current instruments (such as a heating of less than 0.1°C).
However, many studies have shown that biological effects may be present for these non-thermal exposures. Various mechanisms have been proposed to explain biological effects from non-thermal exposures (Binhi, 2002), and there may be several mechanisms at work underlying the differing phenomena observed. Biological effects of weak electromagnetic fields are the subject of study in magnetobiology.
Many subtle, and at times, not-so-subtle effects on behaviour have been reported from exposure to magnetic fields, with a particular focus in research on pulsed magnetic fields. The specific pulseform used appears to be an important factor for the behavioural effect seen. For instance, a pulsed magnetic field originally designed for magnetic resonance spectroscopic imaging was found to alleviate symptoms in bipolar patients (Rohan et al, 2004), while another MRI pulse had no effect. A whole-body exposure to a pulsed magnetic field was found to alter standing balance (Thomas et al, 2001) and pain perception (Shupak et al, 2004) in other studies.
TMS (and related)
A strong changing magnetic field can induce electrical currents in conductive tissue, such as the brain. Since the magnetic field will penetrate tissue, it can be generated outside of the head to induce currents within, hence Transcranial magnetic stimulation. These currents will depolarize neurons in a selected part of the brain, leading to changes in the patterns of neural activation. Essentially, the effect of TMS is to change the information content in the neurons. There is no structural or heating effect that may damage the tissue; only natural signals (action potentials) are generated in the target area. If there are any risks, these are due to the arrival of action potentials to synapses and the natural activation of the postsynaptic cell.
A number of scientists and clinicians are attempting to use TMS to replace electroconvulsive therapy (ECT) to treat disorders such as severe depression. Instead of one strong electric shock through the head as in ECT, a large number of relatively weak pulses are delivered in TMS treatment, typically at the rate of about 10 pulses per second.
If very strong pulses at a rapid rate are delivered to the brain, the induced currents can cause convulsions. Sometimes this is done deliberately in order to treat depression such as in ECT.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Bioelectromagnetics". A list of authors is available in Wikipedia.|