Why is Pain in the Face and Head Worse than the Rest of the Body?

Researchers have found why pain from the head and face can be more disruptive, and emotionally draining than pain in other parts of the body. The researchers found that sensory neurons from the head and face are wired directly into the brain’s principal emotional signaling hubs, while sensory neurons from elsewhere in the body are connected only indirectly to this hub. People consistently rate pain of the head and face as more disruptive and emotionally draining than pain in other parts of the body. The results may help lead toward more effective treatments for pain mediated by the craniofacial nerve, including chronic headaches and neuropathic face pain.

Usually doctors focus on treating the sensation of pain, but this work demonstrates that doctors need to also treat the emotional aspects of pain. Pain signals from the head and face compared to 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. Even so, differences in sensitivity would not explain the greater fear and emotional suffering that patients experience in response to head and face pain than pain in other parts of the body. Functional Magnetic Resonance Imaging (fMRI) shows greater activity in the amygdala, a region of the brain involved in emotional experiences, in response to head pain than in response to body pain. It has been observed in human studies that pain in the head and face seems to activate the emotional system more extensively.

To examine the neural circuitry underlying the two different types of pain, the researchers tracked brain activity in mice after irritating either the face or a paw.  Irritating the face led to higher activity in the brain’s parabrachial nucleus (PBL), a region directly wired into the brain’s instinctive and emotional centers. The researchers used methods based on a novel technology, called CANE, to pinpoint the sources of neurons that caused this elevated PBL activity. Further experiments showed that activating this pathway prompted face pain, while silencing the pathway reduced it.

The researchers feel the results of this study can help lead to a more profound understanding of chronic head and face pain and translating this insight into treatments that will provide benefit. Chronic head-face pain from headaches and trigeminal neuralgia is often very severe and sometimes led patients to seek surgical solutions such as severing the known neural pathways that carry pain signals from the head and face to the hindbrain. These surgeries do not always stop the pain though.  The discovery of this direct pain pathway might provide an explanation why facial pain is more severe and more unpleasant than other types of pain. The researchers feel that targeting the neural pathway identified in the work can be used toward developing innovative treatments for head and face pain.

This work should help people undergoing wisdom teeth removal understand that if complications occur they can be potentially be very painful and long lasting, such as the chronic headaches experienced by the author of this site and blog.

Source: Erica Rodriguez and et al., A craniofacial-specific monosynaptic circuit enables heightened affective pain, Nature Neuroscience, 2017.

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