The Perception of Pain

                                                            The Perception of Pain

            I have never met anyone who has not experienced pain, either physical or emotional.  However, while pain is indeed universal, it is also highly individualized.  While this individualized perception of physical pain makes some sense, it is harder to grasp the relationship between the emotional pain that a person experiences and the physical symptoms that the body produces in response to that emotional pain. This relationship is further complicated by the fact that these physical responses to emotional pain are highly individualized.  Looking at the perception and interpretation of pain, both physical and emotional, helps to understand the degree to which each nervous system is unique as well as the interconnectedness between the body and the mind.      

There are many different types of pain and theories about what causes physical pain.  The first type is nociceptive pain,which is the reflexive, physiological response to acute pain that acts as an early warning system.  It can also manifest in the temporary, inflammatory response that is used to protect an injury from further damage (Munro). The second type of physical pain is neuropathic pain, which is characterized by damage to the nervous system and usually accompanies a specific disease.  The third type is classified as chronic pain, which is characterized as “joint and muscle tenderness associated with pain disorders such as fibromyalgia or backpain" (Munro).  However it is also marked by dispersed visceral pain that does not serve any biological purpose and is not connected to any injury or damage of the nervous system.  Chronic pain is slightly problematic from a biological standpoint since it is not the result of an apparent injury of any kind.  In addition, most emotional pain manifests itself as dispersed pain, which makes its diagnosis and treatment even more difficult.

There are two main theories about the neurobiological mechanisms that cause pain.  The first is the gate control theory,which proposes that there is a mechanism in the brain that acts as a gate to increase or decrease the flow of nerve impulses from the peripheral fibers tothe central nervous system.  An open gate allows for the flow of nerve impulses, allowing the brain to perceive pain.  A closed gate, on the other hand, does not allow flow of nerve impulses, therefore decreasing the perception of pain (Helms, 2008). The second proposed theory, is the neuromatrix theory, which is a continuation of the first, and states that each person has a genetically built-in network of neurons called the “body-self neuromatrix.”  Each person’s matrix of neurons is unique and is affected by the person’s physical, psychological, and cognitive makeup, in addition to their own experiences.  This unique neuronal connectivity, in addition to individual experiences, interacts to create an individuals personal sense of pain.  Therefore, there is not a direct relationship between tissue damage and pain (Helms, 2008). 

All three types of pain are initially detected by nociceptors, or pain receptors, which are free nerve endings that respond to painful stimuli.  In addition to their presence in most bodily tissues, they transmit information back to the brain and are stimulated by biological, electrical, thermal, mechanical, and chemical stimuli.  A person perceives pain when these stimuli are transmitted to the spinal cord and then to the brain.  The pain signal begins in the thalamus,continues on to the limbic system, which is the emotional center for pain and then goes to the cerebral cortex, where the pain is interpreted (Helms,2008).  Although this pathway makes sense for physical pain it is interesting to consider the pathway’s implications for the physical manifestation of emotional pain.  Since these fibers require some sort of trigger, presumably a physical one, then does that mean that our emotional pain is accompanied by a physical response? If so, then does that not also mean that all of our emotions produce physical responses?  It would seem that we are no longer able to look at the mind and the body as two distinct entities but rather as one that experiences the world in two different ways, physically and emotionally, and turns information from both into a single response.  

It is interesting to consider that the sensation of pain can be blocked by triggering fibers that generate non-painful stimuli.   Touch receptors are an example of a type of fiber that can transmit non-painful stimuli and block pain impulses from reaching the thalamus (Helms, 2008). In addition to specific neural fibers that can be activated to block pain impulses, the body has a built in chemical mechanism to manage pain.  Fibers in the brain stem and peripheral tissues release neuromodulators, also known as endogenous opiods that inhibit the action of neurons that transmit pain impulses.  Some examples of naturally occurring opiods are beta-endorphins and dynorphins (Helms, 2008).  It is thought that these opiods play a key role in the placebo effect since a person’s expectations about pain can modify and alter their perception of pain by altering the pain mechanisms in the spinal chord.  However, it is interesting to think that a person’s experience of physical pain can be changed depending on their mental state and their expectations of what that pain will be.  

While there is very little information on the biological effects of emotional pain, scientists agree that it is just as real and intense as physical pain.  However, it is believed that while both types of pain hurt when they occur, that the memory and pervasiveness of emotional pain long outlasts physical pain, suggesting that while most physical pain dulls over time, emotional pain does not.  It is known that the pain network in the brain consists of the dorsal anterior cingulate cortex (dACC), the insula (Ins), the sotosensorycortex (SCC), the thalamus, and the periaqueductal gray (PAG).  This pain network is triggered when a person experiences either physical or emotional pain.  In addition, it is thought that the brain treats both types of pain in a similar manner since the there is only one pain network, for both types of pain, and it is triggered when a person experiences either type (Eisenberger, 2009).  In support of this theory, scientists believe that chronic pain and depression are thought to share the same physiological pathway. Patients with chronic pain, who have been given antidepressants and selective serotonin reuptake inhibition, which are used to treat depression, have experienced much relief. Antidepressants work by blocking the reuptake of neurotransmitters such as epinephrine and norepinephrine, which results in altering neurotransmission along pain pathways (Helms, 2008). Since several areas of the brain are involved in the fast defensive processing of nociceptive pain are also involved in the cognitive appraisal of pain, it is thought that a persons physical experience of pain is directly correlated to their emotional experience of pain.  Factors that affect this relationship are a person’s emotional context, and their expectation of pain.

 Dubner, Ronald, and Michael Gold. "The Neurobiology ofPain." PNAS 96 (1999): 7627-7630.

Lieberman, Matthew, and Naomi Eisenberger. "Pain andPleasures of Social Life." Science 5916th ser. 323 (2009): 890-91.

Blackburn-Munro, Gordon, and Ruth Blackburn-Munro. "Pain inthe brain: Are hormones to blame?" Trends in Endocrinology andMetabolism 14 (2003): 20-27.

Helms, Jennifer. "Physiology and Treatment of Pain."Critical Care Nurse 28 (2008): 38-49.