The following is an excerpt from Dr. Mel Pohl’s award winning book about chronic Pain Recovery, “”A Day Without Pain”. Scientists have long understood that the feeling of pain is located in the brain; hence, “no brain, no pain.” To understand the biology of pain, let’s look at what happens when you get a nail stuck in your finger (see Table 1). The painful stimulus travels along a pathway up the spinal column, which then activates the pain center in the brain. Typically, an injury always produces a painful experience that matches the injury, and there should be no pain without injury. In other words, it’s an alert signal, like a fire alarm going off, telling us that something is wrong and to do something. Chronic pain, however, where there is pain but no ongoing injury or in cases where pain stays around after an acute injury has healed, simply does not make sense. The fire alarm isn’t needed any longer because we’re alert, but we can’t turn it off. To further explain this, research has shown that pain signals are sent to the brain through many routes. Functional magnetic resonance imaging (fMRI) studies have demonstrated that the experience of pain is actually recorded in many different areas of the brain simultaneously. As discussed throughout this site, pain is based not just on a physical event, but also on your responses to the physical event: thoughts, emotions, and behaviors, which are affected by your gender, race, religion, social status, age, and so forth. It is the emotional experience of pain that has been shown to be especially important to your perception of pain and, ultimately, your suffering. The main area in the midbrain where you form and register emotions is the limbic system. The limbic system is a set of brain structures that surround the thalamus (the pain-processing center) and is responsible for filtering and prioritizing all the impulses your brain receives. The limbic system is a central core of structures below the cerebral cortex. These structures include the hypothalamus, hippocampus, insula, basal ganglia, and amygdala. In addition to emotions, the limbic system has much to do with memories.
- The hypothalamus is a tiny area in the brain concerned with homeostasis, which keeps things level and even. If something changes, the hypothalamus is charged with returning us to a set point, like a thermostat. It regulates your body temperature, pulse, blood pressure, aggressive feelings, breathing, hunger, and arousal in response to emotional situations, thirst, pleasure, anger, sexual satisfaction, and more. The hypothalamus is also partly responsible for your responses to pain.
- The amygdalae are two small clumps of nerve cells on each side of the thalamus at one end of the hippocampus. They are involved in sexual responses, anger, aggression, and fear. They are the alert center—the initial warning system for the rest of the nervous system.
- The hippocampus is made up of two “horns” that curve back from the amygdalae. It is important in changing short-term memories into long-term memories and recording and recalling memories.
- The basal ganglia are located deep within the cerebral hemispheres in the back of the brain and are responsible for how you acquire and process knowledge, the coordination of movement, and voluntary movement.
- The insular cortex, also known as the insula, is part of the cerebral cortex. It is involved in virtually every human emotion and behavior. The insula controls perception, motor control, self-awareness, cognitive functioning, and interpersonal experience. It is also the part of the brain that judges the degree and significance of pain.
The limbic system operates by influencing the endocrine (hormone) system and the autonomic nervous system. It is linked to smell, learning, memory, thinking, and sexual function, and helps you integrate functions connected to personal experiences. The limbic system is interconnected with the nucleus accumbens, the brain’s “pleasure” or “reward” center. The nucleus accumbens plays a role in sexual arousal, as well as in getting high from certain drugs. This simple diagram represents general areas of the brain. Other areas of the brain that function in concert with the limbic system include:
- The cingulate gyrus, which provides a path from the thalamus to the hippocampus and is believed to be responsible for focusing attention on emotionally significant events and for associating memories with smells and pain.
- The ventral tegmental area of the brain stem, consisting of pathways that are responsible for pleasure and reward.
- The prefrontal cortex, involved in planning for the future and taking action. It also appears to be involved in the same pathways as the ventral tegmental area and plays a role in addiction reward and pleasure.
- The somatosensory cortex, which processes input from the various systems in the body that are sensitive to touch. There are a number of different sensory experiences involved in touch, including specific sensitivity to pain and sensitivity to temperature. The somatosensory cortex is extremely sensitive, allowing people to detect and interpret a wide variety of sensations.
The autonomic nervous system plays an important role in emotions, and therefore has an impact on your experience of pain. It is made up of two parts, the sympathetic nervous system and the parasympathetic nervous system. These two systems function in opposition to each other. When they are in balance, homeostasis is achieved and the brain is balanced—you feel awake and comfortable. The sympathetic nervous system prepares you for the kinds of activities associated with running from danger or preparing to fight it. It makes your heart pound, stimulates sweat glands, opens the bronchial tubes of the lungs, opens the eyes, and dilates the pupils (called the “fight-or-flight” response). This system also accepts information concerning pain in the internal organs. Because the nerves that carry information about organ pain also carry information about pain from other areas of the body, the information occasionally gets confused. This is the basis for referred pain. A good example of referred pain is when someone feels pain in their jaw or arm when they’re having a heart attack. Nerve cells communicate by the transmission of certain chemicals called neurotransmitters. Neurotransmitters are involved with the experience of pain and all emotions. These chemicals are responsible for sending between nerves information about the pain and/or emotions being sensed. Many different types of nociceptors and brain centers receive this information and cause a variety of phenomena in the body. Neurotransmitters are classified based on whatever stimulus or stimuli they react to. Some examples of a few neurotransmitters (there are hundreds of different neurotransmitters) and what they affect include:
- Epinephrine (adrenalin)—increases heart rate, contracts blood vessels, dilates air passages; also involved with the fight-or-flight response governed by the sympathetic nervous system.
- Norepinephrine (noradrenalin)—wakefulness, anxiety, alertness; also involved in pain.
- Dopamine—associated with addiction, love, basic rewards, drives for pleasure, and voluntary movement.
- Acetylcholine—voluntary movement and the regulation of smooth muscle and cardiac muscle. In the central nervous system, acetylcholine is involved in learning, memory, and mood.
- GABA (gamma-aminobutyric acid)—turnoff of motor neurons, resulting in relaxation and sleepiness.
- Serotonin—memory, emotions, mood, appetite, wakefulness, sleep, and temperature regulation. Serotonin also decreases pain.
During years of many former chronic pain clients, their limbic systems were on tilt. Fear, anger, and frustration all became pain. This was because his dopamine, serotonin, and GABA levels were at low levels. Their levels of epinephrine and norepinephrine were chronically elevated, causing them to feel anxiety, heart palpitations, more fear, and general uneasiness. They couldn’t sleep, their appetite was off, and they were extremely irritable—all because of imbalances in their central nervous systems. Their parasympathetic nervous systems were underactive. The parasympathetic nervous system’s job is to return the body to its normal state after an emergency. Among other things, it decreases heart rate, constricts the bronchial tubes, constricts the pupils, and calms you down. These clients couldn’t seem to settle down and relax. Their anxiety was running rampant, and there seemed to be nothing they could do about it except drink or take other drugs, which offered temporary relief. From brain research, scientists have learned that specific pain centers exist that have evolved from the areas of the brain that control the body. According to one study, the overlap between these areas and emotion processing regions of the brain explains the subjective qualities of human pain. Jodie Anne Trafton, Ph.D., director of the Veterans Administration Palo Alto Health Care Systems Program Evaluation and Resource Center in California, further explains that pain is part of an interoceptive (or “well-being”) system that tells you how you’re feeling. This system, which involves the highly specialized areas of the brain I just described, is programmed differently from your other senses and is linked to the limbic and autonomic nervous systems. In addition to giving you a sense of yourself, the well-being system motivates you into action to correct internal states. In other words, it adjusts most of your functions, behaviors, internal “climate” (for example, blood pressure, heart rate, stomach acid), and emotions. It organizes and processes all the input and judges the importance of each of these internal states depending on the results—you sit down, yawn, go to the fridge, doze off, or become anxious. All these actions are attempts to return the organism (you) to a balanced state. Dr. Trafton has been one of my best teachers about chronic pain. She describes research using functional magnetic resonance imaging (fMRI), which has shown that the area of the brain that controls the well-being system is activated by heat, exercise, anger, seeing emotions on the faces of others, and, most importantly, chronic pain. Basically, what this means is that you have an extremely complicated and complex system in your body that processes information about how you’re doing in the world. The incoming information becomes your feelings, and you respond with drives. “As pain becomes chronic, the sensory components become less important and the emotional and behavioral components tend to take on more importance,” Trafton says. “It is because of learning. Having pain is a strong emotional experience. It will reshape your behavior. It will reshape how you interact with the world. And that in itself means your brain is going to respond differently over time.” In fact, researchers now know that when the brain responds differently, it actually changes physically and becomes different. Emotion and pain have caused the brain to change.