The Perception of Pain

kdillard's picture

 

                                                            ThePerception of Pain

            Ihave never met anyone who has not experienced pain, either physical oremotional.  However, while pain isindeed universal, it is also highly individualized.  While this individualized perception of physical pain makessome sense, it is harder to grasp the relationship between the emotional painthat a person experiences and the physical symptoms that the body produces inresponse to that emotional pain. This relationship is further complicated by the fact that these physicalresponses to emotional pain are highly individualized.  Looking at the perception andinterpretation of pain, both physical and emotional, helps to understand thedegree to which each nervous system is unique as well as the interconnectednessbetween the body and the mind.      

There are many differenttypes 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 anearly warning system.  It can alsomanifest in the temporary, inflammatory response that is used to protect aninjury from further damage (Munro). The second type of physical pain is neuropathic pain, which ischaracterized by damage to the nervous system and usually accompanies aspecific disease.  The third typeis classified as chronic pain, which is characterized as “joint and muscletenderness associated with pain disorders such as fibromyalgia or backpain" (Munro).  However it isalso marked by dispersed visceral pain that does not serve any biologicalpurpose and is not connected to any injury or damage of the nervoussystem.  Chronic pain is slightlyproblematic from a biological standpoint since it is not the result of anapparent injury of any kind.  Inaddition, most emotional pain manifests itself as dispersed pain, which makesits diagnosis and treatment even more difficult.

There are two maintheories 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 toincrease or decrease the flow of nerve impulses from the peripheral fibers tothe central nervous system.  Anopen gate allows for the flow of nerve impulses, allowing the brain to perceivepain.  A closed gate, on the otherhand, does not allow flow of nerve impulses, therefore decreasing theperception of pain (Helms, 2008). The second proposed theory, is the neuromatrix theory, which is acontinuation of the first, and states that each person has a geneticallybuilt-in network of neurons called the “body-self neuromatrix.”  Each person’s matrix of neurons isunique and is affected by the person’s physical, psychological, and cognitivemakeup, in addition to their own experiences.  This unique neuronal connectivity, in addition to individualexperiences, interacts to create an individuals personal sense of pain.  Therefore, there is not a directrelationship between tissue damage and pain (Helms, 2008). 

All three types of pain are initially detected by nociceptors, or painreceptors, which are free nerve endings that respond to painful stimuli.  In addition to their presence in mostbodily tissues, they transmit information back to the brain and are stimulatedby biological, electrical, thermal, mechanical, and chemical stimuli.  A person perceives pain when thesestimuli 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 andthen goes to the cerebral cortex, where the pain is interpreted (Helms,2008).  Although this pathway makessense for physical pain it is interesting to consider the pathway’simplications for the physical manifestation of emotional pain.  Since these fibers require some sort oftrigger, presumably a physical one, then does that mean that our emotional painis accompanied by a physical response? If so, then does that not also mean that all of our emotions producephysical responses?  It would seemthat we are no longer able to look at the mind and the body as two distinctentities but rather as one that experiences the world in two different ways,physically and emotionally, and turns information from both into a singleresponse.  

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

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

 

 

Comments

Paul Grobstein's picture

pain: physical and emotional?

"all of our emotions produce physical responses" because our emotions are theselves physical, ie patterns of activity in neurons?  If so, what exactly is the distinction between "physical" and "emotional" pain?

"these fibers require some sort of trigger, presumably a physical one"  But neurons can be active without an external trigger, no?  So perhaps not all pain originates in nociceptors? 

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