Targeting a specific part of the brain with weak alternating current of electricity significantly decreased chronic lower back pain in all participants of a small clinical trial, researchers report.
The results suggest that doctors may one day be able to target parts of the brain with new noninvasive treatment strategies, such as transcranial alternating current stimulation, or tACS, to boost naturally occurring brain waves researchers theorize are important for the treatment of chronic pain.
“We’ve published numerous brain stimulation papers over several years, and we always learn something important,” says senior author Flavio Frohlich, director of the Carolina Center for Neurostimulation and associate professor of psychiatry at the University of North Carolina at Chapel Hill.
“But this is the first time we’ve studied chronic pain, and this is the only time all three elements of a study lined up perfectly. We successfully targeted a specific brain region, we enhanced or restored that region’s activity, and we correlated that enhancement with a significant decrease in symptoms,” Frohlich says.
“If brain stimulation can help people with chronic pain, it would be a cheap, non-invasive therapy that could reduce the burden of opioids, which we all know can have severe side effects,” says co-first author Julianna Prim, a graduate student in the allied health sciences department who Karen McCulloch, who works closely with Frohlich’s lab, mentored.
Stuck in a neural rut
Chronic pain is the leading cause of disability in the world, but there is not consensus among scientists that brain activity plays a causal role in the condition.
The pain research field has focused largely on peripheral causes of chronic pain, Frohlich says. For example, if you have chronic lower back pain, then the cause and solution lie in the lower back and related parts of the nervous system in the spine.
But some researchers and clinicians believe chronic pain runs deeper, that the condition can reorganize how cells in the nervous system communicate with each other, including networks of neurons in the brain. Over time, the theory goes, these networks get stuck in a kind of neural rut, essentially becoming a cause of chronic pain.
Previous studies showed that people with chronic pain experience abnormal neural oscillations, or brain waves. There are several kinds of brain waves related to different brain regions and various kinds of brain activities, such as processing visual stimuli, memorization, and creative thinking.
When we speak, think, eat, play sports, watch television, daydream, or sleep, our brain activity creates electrical patterns researchers can measure using electroencephalograms, or EEGs. These patterns fluctuate or oscillate, which is why they appear as waves that rise and fall on an EEG printout.
In the zone
One type of brain activity is called alpha oscillations, which occur when we’re not taking in stimuli. When we meditate in silence, daydream in the shower, or even when we’re “in the zone” during athletic activity, alpha oscillations dominate the brain.
Frohlich’s lab wanted to know if these alpha oscillations were deficient in the somatosensory cortex, located in the middle portion of the brain and likely involved in chronic pain. If so, then could researchers enhance the alpha waves there? And if that were possible, would there be any pain relief?
For the study, which appears in the , Prim and colleagues recruited 20 patients with lower chronic back pain. Each of them reported back pain as “four” or greater for at least six months on the subjective scale of one to 10. Each participant volunteered for two 40-minute sessions that took place one to three weeks apart.
During all sessions, researchers attached an array of electrodes to the scalps of patients. During one session, researchers targeted the somatosensory cortex using tACS to enhance the naturally occurring alpha waves. During another session for all participants, researchers used a similar weak electrical current that was not targeted—this was a sham or placebo stimulation session.
During all sessions, participants felt tingling on their scalp. They could not tell the difference between the sham and tACS sessions. Also, the researchers in charge of analyzing the data did not know when each participant underwent the sham or tACS sessions, making this study double-blinded.
Pain reduction
An analysis of the data shows that researchers could indeed successfully target and enhance alpha oscillations in the somatosensory cortex of people with chronic lower back pain.
When Prim and colleagues surveyed the participants, all of them reported a significant reduction in pain immediately following the tACS sessions, according to the subjective 0-10 pain scale. Remarkably, some participants reported feeling no pain after the tACS sessions. Participants did not report the same pain reduction after the sham stimulation sessions.
“The exciting thing is that these results occurred after just one session,” Prim says. “We hope to conduct a larger study to discover the effects of multiple tACS sessions over a longer time period.”
The National Institutes of Health and the North Carolina Translational and Clinical ¾ÅÐãÖ±²¥s (NC TraCS) Institute funded the work. Transcranial alternating current stimulation is not electroconvulsive therapy (ECT), or shock therapy. The amount of electrical current used for tACS is about 1,000 times less than ECT.
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