Prolonged musculoskeletal pain was induced by injecting a substance into the masseter muscle

Researchers have flipped the script on the usual approach to pain relief in a new study, demonstrating that a short course of non-invasive brain stimulation before a painful event such as surgery can prevent the development of chronic pain.

All the way back in 2006, we wrote about a "new technology" called transcranial magnetic stimulation or TMS. Since then, we've covered the promise this non-invasive treatment has shown in treating disorders such as depression and phobias, and in boosting memory.

Now, in a new study, researchers from the University of New South Wales (UNSW) and Neuroscience Research Australia (NeuRA) have demonstrated that a short course of treatment with TMS before the onset of pain can prevent it from becoming a chronic issue.

"Our research showed that repetitive transcranial magnetic stimulation, or rTMS, which is a non-invasive brain stimulation, could be delivered in a preventive way, before pain takes hold," said Nahian Chowdhury, PhD, a registered psychologist, NeuRA research fellow, lecturer at UNSW and the study's lead author.

Whether at home or in the hospital, pain is ordinarily treated after it's started. Sometimes, it's well after, when pain has become a long-term problem. With their current study, the researchers are seeking to shift the paradigm and adopt a more proactive, prophylactic approach to pain management. They foresee rTMS being administered prior to the painful experience - a planned surgery, say, or dental procedure.

"The biggest application for this [treatment] would be prior to any anticipated surgery or medical procedure that involves pain," Chowdhury explained to New Atlas. "Given higher pain after a surgery or procedure is a risk for [developing] chronic pain, reducing this with a pre-operative intervention could prevent chronic pain from happening."

rTMS is a mild form of brain stimulation that uses a series of short magnetic pulses to stimulate the nerve cells, or neurons, in a particular area of the brain. The premise of the treatment is that the pulses alter the neurons' firing pattern, resulting in a change in brain behavior that lasts beyond the stimulation period.

For the present study, the researchers recruited 41 healthy adults - 23 females and 18 males with an average age of 23. Individuals were excluded if they had any sort of acute pain, a previous history of chronic pain, major medical complaints, psychiatric conditions, or where TMS was contraindicated (e.g., metal implants in the skull or epilepsy).

Participants were randomly assigned to receive five sessions of rTMS or a sham treatment over 26 days. Those in the active treatment group received high-frequency rTMS over the left primary motor cortex or M1. In addition to its essential role in initiating movement and controlling voluntary motor behavior, studies have implicated M1 in the modulation of pain perception. So, the researchers targeted that region of the brain.

Key brain activity measures were assessed at baseline and on day four. They included peak alpha frequency (PAF), which reflects performance across cognitive functions like attention, arousal and memory, and corticomotor excitability (CME), which is the strength of the response cortical neurons have to stimulation. At the end of the fourth day, participants were given an injection of human nerve growth factor into the right masseter muscle, one of the jaw muscles involved in chewing, to induce prolonged musculoskeletal pain, analogous to temporomandibular joint (TMJ) pain.

"For this trial, we had to induce pain in the participants, which we did through an injection in their right cheek," said Chowdhury. "We were looking to see what the experience was for the participants who had received the rTMS, versus what happened for those who had received the sham. Those people who had received active rTMS experienced lower pain on chewing and yawning than those who received the sham."

While a five-day course of rTMS didn't lead to lower pain on talking or reduce limitations on jaw mobility across the three-week study period, the researchers noted there were stronger reductions in pain at earlier time points compared to the sham treatment. Additionally, rTMS didn't alter the severity or duration of pain associated with swallowing, smiling, drinking, pain at rest, or muscle soreness. However, the researchers observed that faster PAF and higher CME on day four were associated with less intense future pain, suggesting that these metrics could be used to predict someone's pain resilience.

"We have for many years been primarily applying rTMS during chronic pain states, where it is difficult to reverse maladaptive brain activity," Chowdhury told New Atlas. "Focusing on preventing chronic pain before it happens could therefore be an impactful field of work that deserves more attention!"

The researchers are looking at using rTMS on brain regions other than the primary motor cortex. Chowdhury referred to a pre-print study he led that examined the effectiveness of rTMS on the posterior-superior insula cortex, an area concerned with recognizing, encoding, localizing, and remembering painful events. That study found that using TMS to stimulate that region reduced heat pain sensitivity.

Regarding the present study, more research is needed to investigate the potential for rTMS to be used to prevent the development of chronic pain.

"Chronic pain is a global health issue, impacting patient quality of life and healthcare systems," Chowdhury said. "We looked at how we can support the body before a pain event, and before pain is chronic, by targeting the features of cortical activity associated with chronic pain susceptibility.

"More research is required, but this research shows in some situations - such as for people undergoing a surgery known to be painful or often leading to chronic pain - there is promise from preventive treatments that may be able to stop chronic pain before it begins."