A newer area of research in the management of pain is the use of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS). Both these areas of research were started in the 1990’s and have been shown to provide some degree of pain relief. The most difficult part of these technologies is knowing what is being stimulated, and being able to effectively target specific regions of the brain. Both techniques are generally believed to be non-invasive since stimulation is superficial to the skin. Additionally, both of these technologies are still basically considered experimental.
rTMS and tDCS
Repetitive transcranial magnetic stimulation is more complex than tDCS. A magnetic coil is held near the scalp and a current though the coil creates an intense magnetic pulse that passes through the scalp to the brain and depolarizes neurons while altering brain signals. The magnetic pulses need to be aimed using MRI guidance. Further, signals can be given at different frequencies, and high frequency treatments may have some effect on pain, but they do not tend to last much beyond the treatment sessions that are done daily. It is thought that the magnetic pulses can affect the cognitive and emotional aspects of pain perception.
Transcranial direct current stimulation (tDCS) is simpler in application and cost, but full understanding of its mechanisms of action are less clear. It is believed that the current triggers changes at the cellular level in the brain in the form of an analgesic effect, and it also changes the way pain signals are transmitted. The technique involves sending weak currents across the scalp, either exciting neurons or inhibiting neurons by the way the current travels between electrodes. A variety of portable devices and protocols are being developed to deliver appropriate signals. The placement of electrodes and the pattern, intensity and frequency of currents used is being investigated. The most common use of these techniques are for headaches, neuropathic pain and fibromyalgia. Combining tDCS with aerobic exercise has been found to be especially helpful for some fibromyalgia patients.
So far the risks of these technologies has been found to be relatively low for adverse events. rTMS has the most risks, as it can affect blood pressure, breathing and seizures. tDCS has no significant known risks at this time, but since it could affect moods, it may have negative effects on issues like depression. How these new techniques will be incorporated into effective pain management strategies is far from clear. Since we know many pain conditions stem from how the brain is perceiving or misinterpreting sensory signals associated with pain receptors, changing the transmission of these signals in the brain may help manage various conditions.
Thomas Cohn, MD
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