Chronic pain, defined as pain that persists beyond three to six months, is the leading cause of disability in the world. Some studies even suggest that as many as 43 per cent of all UK adults will suffer from this condition at some point in their lives. Unfortunately, there is currently no cure for chronic pain and treatments are far from perfect; misuse of strong and highly addictive pain medications is fuelling the devastating opioid epidemic sweeping across America. The large proportion of patients turning to homoeopathic interventions, despite a lack of evidence for their efficacy, also clearly shows the desperate need for a more effective science-based treatment.
Unfortunately, the underlying causes of chronic pain are not yet clear. Most research so far has focused on peripheral causes. For example, if a person suffers from chronic lower back pain, some researchers think that the cause and treatment solution must lie in the lower back and related parts of the nervous system in the spine. However, other researchers believe chronic pain may actually be associated with a maladaptive injury-induced reorganisation of cells in the brain. This rewiring is reflected in the abnormal brain wave activity that has been recorded in people suffering from chronic pain. These changes in neural activity are often seen in pain-associated regions such as the somatosensory cortex.
Alpha oscillations are the most common type of brain waves in the somatosensory cortex. In a study published in the Journal of Medicine, researchers from the UNC School of Medicine recorded alpha oscillations in the somatosensory cortex of chronic pain patients and found that there was a negative correlation – weaker alpha oscillations were associated with greater levels of subjective pain. They hypothesised that alpha oscillations are impaired in those suffering from chronic pain and wondered whether enhancing these brain waves might provide some pain relief.
The researchers used transcranial alternating current stimulation (tACS) to enhance the alpha oscillations. tACS is the external application of oscillating electrical current which can influence brain wave activity. In this study, 20 patients with chronic lower back pain were given two 40-minute sessions of tACS, one to three weeks apart. In one session they had an array of electrodes attached to their scalps to target the somatosensory cortex with electrical current and enhance naturally occurring alpha oscillations in this area. In the other session, they were given a placebo stimulation. The patients did not know which stimulation was real and which was the placebo.
Surprisingly, all of the patients reported a significant reduction in their subjective pain after just one tACS session and some even reported feeling no pain at all. Participants did not report the same level of pain reduction after the placebo stimulation.
Future work in this area should look at how long it takes for the pain-relieving effect of the stimulation to wear off and whether multiple tACS sessions over a longer period of time might have longer lasting effects. Also, if researchers can determine which brains areas to target with stimulation, this treatment might be able to treat different types of chronic pain such as chronic headaches or trigeminal neuralgia. If this research can be replicated, tACS could be a cheap, non-invasive therapy to provide suffers of chronic pain with some desperately needed relief.
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