Why is Cranio-facial pain worse than everything else?
Pain is weird
Chronic head and face pain and suicidality
Why head and face pain feels worse
The neuroscience of suffering Pain is complicated. It’s even more complicated as a doctor because the expectation from years and years of conditioning is that when you have pain, then something about that painful body part must be damaged to cause it. When people are in pain, doctors are typically trained to identify things like a ruptured disc, broken bone, or torn muscle to validate a patients' sense of suffering. In this model, the more damage that is present = more pain. Less damage = less pain.
Chronic Facial Pain and Suicidality Chronic pain is a known risk for suicidal ideation, and has been documented in numerous studies <source=">source</a>">. These thoughts have a higher chance of turning into behavior when you have chronic pain and a co-morbid mental health disorder <source=">source</a>">. This effect seems most pronounced when the source of the pain is coming from the head or face. Two disorders in particular are highly associated with suicidal thoughts and behavior; trigeminal neuralgia and cluster headaches. Trigeminal neuralgia has a high enough association that it was historically dubbed the 'suicide disease', while cluster headache has been known to be called the 'suicide headache'. Both of these illnesses are associated with some of the most intense pain that human beings can experience. The severity of the pain combined with the chronicity of the pain lead to a sense of despair because these disorders can be difficult to treat, so there is always a fear of the next attack. Scientists have recently uncovered some neurological pathways that might explain why conditions like trigeminal neuralgia and cluster headaches can cause such disproportionate suffering compared to other body pains.
The Trigeminal Complex and the Limbic System It’s been known that pain experienced in the head and face activate the emotional centers of the brain more than pain felt in the periphery of the body <source=">source</a>">. From an evolutionary standpoint, a higher state of pain in the head and neck region may have served a purpose so that there would be extra vigilance in protecting this region of the body from injury. What was unknown was weather this heightened sense of protection was derived from a psycho-social factors, or if it was something that was hard wired into our nervous system. Duke University scientists may have some answers. A 2017 study in Nature Neuroscience showed that neurons in the head and face have a direct pathway to the emotional circuits in the brain. Scientists identified a direct connection between sensory fibers of the trigeminal nerve into a part of the brainstem called the parabrachial nucleus. The parabrachial nucleus has direct connections into the emotional hub of the brain in the amygdala, which is highly tied to fear and avoidance behavior. Why is this important? Because direct, aka, monosynaptic connections are way more powerful sensory stimuli than indirect pathways. Think of it this way: Let's say you were mailing a time-sensitive package that needed to get to it's destination as soon as possible. Would you choose to overnight it by plane, or would you choose regular first-class mail? You probably chose to overnight it right? Why? Because it's going to get there faster, and because the person receiving it is going to perceive that package as more important because it was sent with all of this overnight labeling implying it's importance. These direct pathways are like your overnight deliveries, where the indirect pathways are like ground shipping. Our brains place a higher priority on signals coming from these monosynaptic pathways. While other body regions only use an indirect path to the parabrachial nucleus, the trigeminal distribution uses both indirect AND direct pathways to stimulate this emotional hub. That means that firing from nociceptive pain fibers in the trigeminal distribution, or even pathways that share trigeminal distribution will have a higher chance of driving an emotional response than pain fibers from the shoulder, back, hip, etc.
The Emotional Brain's Influence On Pain How big of an influence does emotion make in the experience of pain? In this study, the researchers stimulated pain receptors in the paw or in the face of mice using a chemical called formalin. Using a technique called optogenetics, researchers can selectively activate brain activity in a mouse model using different light frequencies. When light activated the direct pathway, the mice showed more intense avoidance behavior to the formalin on the face. When light was used to knock out this pathway, the mice didn't react as strongly.
So you have the same amount of pain stimulus, the same mouse, and it experiences pain differently because the path to the parabrachial nucleus was turned off. It suggests that our emotional brain's connection to a painful stimulus plays a substantial role in the experience of pain.