(Reuters Health) – If head and facial pain seem stronger and scarier than pain elsewhere, it’s because a special pathway in the brain is heightening our emotions from pain at those sites, according to studies in mice.
People usually experience head and facial pain as more severe and emotionally draining than body pain, but the biological basis of this remains something of a mystery.
It turns out that pain signals in the face travel to a different place in the brain than pain stimuli in other parts of the body, researchers say.
Dr. Fan Wang from Duke University Medical Center in Durham, North Carolina and colleagues looked at the brain circuitry involved in pain perception in mice, focusing on differences between responses to painful stimuli to the face and to the paw.
They knew already that pain signals from the face travel to both sides of a brain area called the lateral parabrachial nucleus, or PBL. The new study showed that signals traveled from there to multiple centers in the brain related to emotions and instincts.
As it turns out, the brain cells in the PBL also get input from these emotion centers, the researchers explain online November 13 in Nature Neuroscience.
In contrast, pain signals from the paw travel through the spinal cord and end up in a different part of the parabrachial nucleus on the side of the brain opposite the side of the paw that was stimulated.
“Pain, especially chronic pain, is not just a sensory disorder, but also an emotional disorder, and chronic head and face pain directly and robustly affect the patient’s emotional suffering,” Dr. Wang told Reuters Health by email. “Therefore, it is important to treat the emotional suffering of chronic pain patients.”
“We speculate that the reason for this head/face specific neural circuit wiring is perhaps due to the presence of sensory organs for vision, hearing, smell, and taste (essentially for all senses except bodily sense), as well as for vital functions such as breathing, feeding, and vocal communication, and therefore there is a need for a rapid emotional/instinctive response to the noxious stimuli experienced by head/face,” she said.
The study’s findings, Dr. Wang notes, “suggest how painful information is processed and transmitted is very much dependent on the animal’s internal brain state. In other words, (the) same painful stimulus may feel differently (more or less severe) depending on the ongoing emotional states.”
Dr. Arne May from Universitaetsklinikum Hamburg Eppendorf in Germany, who has researched facial pain extensively, told Reuters Health by email, “Most will be surprised that, indeed, facial pain is perceived as more threatening than (the same) pain of the arm or leg. This work starts to unravel the physiological background.”
“Why this seemingly explicit pathway exists” is still unclear, he said. “Probably because the face/head is more important to the system in terms of survival.”
Dr. Milind Deogaonkar from The Ohio State University in Columbus told Reuters Health by email, “This just validates what I see in my practice of face pain every day. It provides concrete scientific basis to the clinical findings in my practice. I have a large atypical face pain and trigeminal neuropathic pain practice that I treat with neuromodulation.”
Unlike the study authors, though, Dr. Deogaonkar does not favor more extensive surgery to address facial pain. Instead, he would consider more neuromodulation of the brain pathways that contribute to the emotional aspects of pain.
SOURCE: http://go.nature.com/2AXpSUY
Nat Neurosci 2017.
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