Why does the pain one feels in the head, face, eyeballs, ears, and teeth seem more disruptive and emotionally draining than pain elsewhere in the body? Human brains are wired so that this pain is felt more strongly emotionally, researchers say.
Duke University scientists, in a study published recently in Nature Neuroscience, explain that sensory neurons that serve the head and face are wired directly into one of the brain’s principal emotional signaling hubs. Sensory neurons elsewhere in the body are also connected to this hub, but only indirectly.
Pain signals from the head versus those from the body are carried to the brain through two different groups of sensory neurons, and it is possible that neurons from the head are simply more sensitive to pain than neurons from the body, notes a media release from Duke University.
Results from the study may pave the way toward more effective treatments for pain mediated by the craniofacial nerve, such as chronic headaches and neuropathic face pain.
“Usually doctors focus on treating the sensation of pain, but this shows the we really need to treat the emotional aspects of pain as well,” says Fan Wang, a professor of neurobiology and cell biology at Duke, and senior author of the study, in the release.
“There has been this observation in human studies that pain in the head and face seems to activate the emotional system more extensively,” Wang adds. “But the underlying mechanisms remained unclear.”
To examine the neural circuitry underlying the two types of pain, Wang and her team tracked brain activity in mice after irritating either a paw or the face. They found that irritating the face led to higher activity in the brain’s parabrachial nucleus (PBL), a region that is directly wired into the brain’s instinctive and emotional centers.
They then used methods based on a novel technology recently pioneered by Wang’s group, called CANE, to pinpoint the sources of neurons that caused this elevated PBL activity, the release continues.
“It was a Eureka moment because the body neurons only have this indirect pathway to the PBL, whereas the head and face neurons, in addition to this indirect pathway, also have a direct input,” Wang says. “This could explain why you have stronger activation in the amygdala and the brain’s emotional centers from head and face pain.”
Further experiments showed that activating this pathway prompted face pain, while silencing the pathway reduced it.
“We have the first biological explanation for why this type of pain can be so much more emotionally taxing than others,” states Wolfgang Liedtke, a professor of neurology at Duke University Medical Center and one of the study’s co-authors, in the release.
“This will open the door toward not only a more profound understanding of chronic head and face pain, but also toward translating this insight into treatments that will benefit people.”
[Source(s): Duke University, Science Daily]