We publish in the journal PAIN reports a new study that advances our understanding of the complex and multifaceted brain signals that convey the perception of pain.

This study was led by Dr. Cecile de Vos when she was a CIHR Postdoctoral Fellow in the lab (now a staff researcher at Erasmus University Rotterdam). The core of the data collection and analyses was conducted by Hyerang (Hannah) Jin, in the context of her undergrad research project.

A press release is at the bottom of this page.

Motivation for the study

Imagine your body's ability to turn down pain like a natural volume control. This ability can be explored in the lab via a technique called Conditioned Pain Modulation (CPM). CPM is a fascinating phenomenon where one pain diminishes the feeling of another.

In the present study, we aimed to unravel the brain activity foundations behind this process, especially in people experiencing chronic pain — a major debilitating condition that affects tens of million in Canada and worldwide. By studying how our brains respond to multiple pain signals, competing to get out attention, we sought to understand the mechanisms at play and how they might be altered in chronic pain conditions.

CPM involves exposing individuals to one painful stimulus that is maintained while another is applied elsewhere on their body. We used this approach by presenting noxious electrical stimuli to the right ankle before, during, and after CPM induced by an ice pack placed on the left forearm. This experimental protocole unfolded while we measured the brain activity of chronic pain patients and healthy controls with great temporal resolution with MEG.

Key Findings:

Universal Pain Reduction: Regardless of whether participants had chronic pain or not, CPM consistently reduced both the perceived pain intensity and specific neural responses in the brain (specifically, beta-band oscillations (~30Hz) in the sensorimotor cortex).
Neurological Mechanisms: We uncovered the involvement of both bottom-up and top-down brain signals during CPM, shedding light on how our brains process as a combination of noxious sensory information (e.g., here from the ankle) and of internal signals coming from higher-order cognitive brain circuits. Context, how we pay attention to and expect painful stimulation play pivotal roles in this intricate dance.
In pain research, this two-way highway is thought as a mechanism for pain relief. In the context of CPM, one painful stimulus (the ice pack) can inhibit the perception of another (the stimulus on the ankle).
Clinical Relevance: CPM has real-world implications. In people with chronic pain, our observations confirm that CPM might not work as effectively, hinting at disruptions in their body's natural pain inhibition processes. Our study therefore may help shape future approaches to managing chronic pain, perhaps even paving the way for more effective treatments.

Take-homes

Beta-ERS Dynamics: We measured a specific brain response to stimulations called beta-band Event-Related Synchronization (beta-ERS), consistently observed in all conditions. We observed reduced beta-ERS during CPM, which we align with the role of beta brain activity to top-down control in pain processing.
Attentional Modulation: Reduced beta-ERS during CPM might mean less attention toward the painful stimulus. Although the role of attention in CPM is debated, our study suggests a possible link between beta-ERS and how attention influences our experience of pain.
Motor Processing: Beta-ERS, with its involvement in both attention and motor processing, adds a layer of complexity to how brain processes pain signals . It might reflect the brain's response to “reflex” movements triggered by painful stimuli, although we were careful to deliver stimuli that did not trigger visible movements.
Chronic Pain Insights: We report exploratory findings that hint at lower beta-ERS in chronic pain patients, suggesting a constant CPM state due to them experiencing pain on an ongoing basis. These observations need validation through further studies.
Alpha and Beta Desynchronization: Our study reports changes in brain oscillations related to excitability, providing clues about how the brain initially alerts to pain. Understanding these changes might contribute to our knowledge of how the brain copes with and redirects attention during pain.

Conclusion

With this study, we advanced knowledge about how the sensation of pain can modulated depending on context (CPM). Our data therefore open up new avenues for understanding how our brains manage pain, via complex two-way signals that involve sensorimotor circuits and more cognitive brain regions and networks . We hope our research inspires novel pain management strategies in the future.

The article reporting the study is available in free, open access at the journal.

Press Release:

New Study Unravels Key Mechanisms of Pain Modulation

Montreal, Canada - A new study by McGill University researchers, published in Pain Reports, provides groundbreaking insights into pain modulation. The study, titled "Neurophysiological oscillatory markers of hypoalgesia in conditioned pain modulation," explores how pain perception and related neural oscillations are modified under conditioned pain modulation (CPM), particularly in individuals with chronic pain.

Utilizing a novel approach combining noxious electrical stimuli with magnetoencephalography (MEG), the team observed that both chronic pain patients and control participants experienced a reduction in pain perception and neural responses during CPM. Specifically, a decrease in beta-band (15-35 Hz) oscillations in the sensorimotor cortex was noted, suggesting changes in the cognitive components engaged that contribute to the sensation of pain.

This study offers significant implications for understanding the neurophysiological underpinnings of pain perception and opens new avenues for developing non-invasive pain management strategies. The findings may be particularly beneficial for individuals suffering from chronic pain, potentially leading to improved therapeutic approaches.

The McGill research team believes that these findings mark a significant step forward in pain research, contributing to better clinical management of pain through evidence-based approaches.

Brain and pain: a two-way street.