Until now it has been unclear how the phenomenon of a person’s mindset can affect their experience of pain. For example, a soldier in the midst of battle or an athlete in competition may report that an injury did not feel especially painful in the excitement of action.
Led by the University of Colorado Boulder, a new study has found that while using thoughts to dull or enhance the sensation of pain, the physical pain signal in the brain does not actually change, but works through a separate pathway in the brain. Pain signals are sent by nerves from a wound and is encoded in multiple regions in the cerebrum, but “cognitive self-regulation” (the act of using thoughts to modulate pain, a technique often employed to manage chronic pain) uses this second, newly mapped pathway.
The findings were published in the journal PLOS Biology this month, and illuminates an increased understanding in the neuroscientific world that there is more than one pain system in the brain. New evidence shows that the processing of pain in our brains goes beyond the mere physical pain signal.
In a press release, Choong-Wan Woo, lead author of the study and a doctoral student in CU-Boulder’s Department of Psychology and Neuroscience, confirmed, “We found that there are two different pathways in our brains that contribute to the pain experience.”
The first pathway is responsible for mediating the effects of turning up the intensity of painful stimulation and involves a number of “classic” regions in the brain, such as the anterior cingulate cortex. The second pathway, discovered in the new study, has been found to mediate the effects of cognitive regulation, and involves increasing activity in the medial prefrontal cortex and nucleus accumbens—brain regions that have been known to be involved in emotion and motivation but that do not normally respond to painful events.
This latter pathway may hold some of the keys to understanding the “emotional” aspects of pain, a characteristic of long-term pain and disability.
Other CU-Boulder co-authors of the study are psychology and neuroscience Associate Professor Tor Wager and postdoctoral researcher Mathieu Roy, and Jason Buhle, an adjunct assistant professor at Columbia University.
The study was conducted with participants being given a painful heat stimuli on their arms as their brains were scanned using functional magnetic resonance imaging, or fMRI.
In the first scan, participants were asked to experience the painful heat without thinking of anything in particular. In subsequent scans, the participants were asked to imagine that the sizzling hot heat was actually damaging their skin, a thought that increased their experience of the pain. They were then to imagine, while again being scanned, that the heat was comfort on an extremely cold day … this thought decreased their experience of the pain.
The brain scans were then examined. The signal for physical pain remained the same across all three scenarios, regardless of how the participants rated their pain experience. But a signal in the brain using a second pathway changed in intensity depending on the type of thoughts, or “cognitive self-regulation” that was employed.
The researchers were able to disentangle the two pathways based on recent work done in Wager’s Cognitive and Affective Neuroscience Lab. In 2013, Wager and his colleagues published a study in the New England Journal of Medicine that identified for the first time a distinct brain signature for physical pain.
“Previously people did not have this specific brain marker for pain,” Woo said. “Incorporating that measure, and identifying a separate pathway that makes an independent contribution to pain, is a major innovation of this paper.”
Examiner asked if there were further studies planned for the future and Woo replied, “Yes, we are planning to do a follow-up study to examine how our autonomic system respond to the cognitive self-regulation task used in the PLoS Biology study. In addition, we are trying to identify a distributed brain network that is sensitive to pain independent of nociception.”
Nociception is defined as “the neural processes of encoding and processing noxious stimuli.” This includes pain. It is the afferent activity produced in the peripheral and central nervous system by stimuli that have the potential to damage tissue. This activity is initiated by nociceptors, (also called pain receptors), that can detect mechanical, thermal or chemical changes above a set threshold.
Examiner also had the welcome opportunity to ask of Woo if perhaps the second pathway in the brain for pain would be linked, in an athlete, more perhaps to the emotion connected to winning or losing, rather than to a chemical reaction in the brain caused by the activity itself?
Woo kindly responded , “When considering previous studies (this is a reverse inference, so we need be cautious to say this, but) it is possible that the second pathway (the nac-vmpfc pathway) is closely linked to motivation and/or valuation regarding pain, and this might be mediated by some brain chemicals, such as dopamine or endogenous opioids. However, this should be tested in the future.”
