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Biology 202
2002 Second Paper
On Serendip

The Human Perception of Pain

Cass Barnes

There is more research surfacing supporting the notion that people can control their pain. What is left under-examined is the notion of whether the pain is mediated by the brain, mind, or both. We all know that pain is an instinctive "sense" if you will, necessary to the survival of all living beings. Without pain, it would go unrecognized and exacerbate to the point of death. Pain is a protective mechanism essential to survival. There are three important claims here: One is that pain is actually a perception. The second, is the brain mediates the suppression of pain through a "gate" in the spinal cord. Lastly, since pain is a perception, the mind may decide the degree to which the "gate" is open, which therefore influences to amount of pain reaching the brain. Recent research provides evidence that certain brain structures mediate the spinal cord gate. Still controversial is whether receptivity to pain is biological in origin and completely dependent on the brain, or whether the mind, the entity in an individual responsible for thought, and feelings, conscious or unconscious, controls the nervous system and in the end manipulates one's perception of pain.

Pain is defined by the International Association for the Study of Pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage" (1). When pain is described in these terms we can see that pain is a perception, sort of like seeing and hearing. When pain is processed there are a number of brain structures activated, commonly referred to as the "central pain matrix" (2). It may seem irrelevant to delve into pain signal activation in the brain since what we are talking about is the brain controlling pain, not receiving it. However, it is important to recognize that when there is an incoming stimulus, it goes to the brain and creates one's perception of pain. In a sense, this means that the brain creates the mental state or the percept of pain. It is also important to discuss the brain structures associated with the pain activation because these structures are essentially the means to the end state of what we call "pain".

The pain process starts out with a stimulus which activates somatosensory axons from the skin, muscles, or internal organs to enter the nervous system via spinal nerves. Axons that convey sharp localized information, like fine touch, ascend through the dorsal columns of the spinal cord, referred to as the fast pathway, to the nuclei in the lower medulla (3). From the medulla, the axons cross the brain and ascend through the medial lemniscus to the ventral posterior nuclei of the thalamus, the somatosensation receiver (bodily sensation). Axons from the thalamus project to the primary somatosensory cortex which are then relayed to the secondary somatosensory cortex. Conversely, axons that convey less localized information, like pain or temperature, ascend through the spinothalamic tract, the slow pathway, and terminate in the ventral posterior nuclei of the thalamus (3),(9). The end site for both of these pathways is in the somatosensory cortex.

These pathways also activate the anterior cingulate cortex, a region of limbic cortex on the medial side of cerebral hemispheres, which processes and understands pain. Studies show that this region is not involved with pure perception of pain, but with the emotional reaction that a painful stimulus can cause. That is, when activated, the aversiveness of pain increases (9). Still under investigation is whether the primary and secondary somatosensory cortex are involved in the perception of pain. A 1997 study produced pain sensations by having subjects put their hands in ice water. Under one condition, the subjects were hypnotized so as to reduce the pain. What they found was that the hypnosis worked in that the pain was not too unpleasant, although intense. The PET scan, a device for detecting brain activity, showed that the stimulus activated both the primary somatosensory cortex and the anterior cingulate cortex. Although the perception of pain remained high with activation of the somatosensory cortex, the anterior cingulate cortex in the hypnotized subject was less active than the others. Those hypnotized also reported less pain even though they could feel ice water. This offers that those who were hypnotized had less of an aversion to the pain although a high perception of pain. Therefore, this system "is activated when a harmful stimulus is potentially threatening to a person, which in turn activates a number of reactions and changes in affect and mood" (2). This change of mood suggests that the stimuli, be it internal or external, lead to the perception of pain. Yet, when a person is not fully conscious, the claim that less pain is produced or perceived, seems valid. In effect, this leads to the idea that the percept of pain may be psychologically induced or reduced. Although pain perception may always be activated with the appropriate stimuli, a person's level of consciousness or degree of interest in the pain may attribute to the intensity of the pain itself. All the while though, the biology of the nervous system seems to be activated first with a noxious stimulus, and with that, this model upholds that the brain creates the mind because the physical structures make the person conscious of perceiving the pain.

Ronald Melzack and Patrick Wall's research of the 1960's proposed the gate-control theory of pain explaining that "pain transmission is blocked from reaching higher centers necessary for perception of pain" (3). This theory holds that ascending and descending pain signals may be blocked in the dorsal horn at the base of the spinal cord therefore inhibiting these areas of the brain from perceiving the pain (3),(4). Essentially, the gate cuts off the ascending axons and disables them from getting to the brain, with the end result being the non-percept of pain. Perhaps the "gate" on those who were hypnotized was closed, therefore allowing less transmission through, and in the end inhibiting pain. However, the study showed that there was still perception of pain, with less aversion to the pain. This would mean that the signals were actually getting through. Therefore, in this case, being less conscious seemed effective in psychologically reducing the perception of pain. On the other hand, when we think about daily "painful" stimuli and how the same stimuli can affect two people differently, it makes one wonder whether the lack of pain perception in one person is a result of the gate closure. Speculatively, the ability to ignore the pain, or not perceive the pain, may be due to the conscious self being in control. This theory suggests that incoming pain is suppressed by certain areas of the midbrain, in particular the anterior cingulate cortex (9).

Perhaps the reason this is mind boggling is because the spinal gate is a hypothetical gate. The spinal gate theory pain is just that, a theory. But, there is still the question of why some people are tougher than others. Are some more susceptible to pain because of childhood rearing in that they never learned mind over matter and how to "close the gate"? What about an Army Ranger? Through disciplinary training he learns to be "tougher" and how to survive with essentially no food or rest, in addition to days of walking and trenching through difficult terrain. Is the ability to suppress the pain from walking for three weeks straight without falling to exhaustion, due to learned behavior, which changes the brain and thus the ability to close the gate to incoming pain? Does one learn to take conscious control of his body and therefore pain? This is where the mind-body connection comes into play.

The mind-body problem argues that there is a relationship of the mind to the body (or brain) and that mental processes affect the physical (5),(6). What the mind is, depends on one's philosophy, but the most common definition is as follows: the entity in an individual responsible for consciousness or unconsciousness, thought and feelings, having its origin in the brain (7),(8). Or, the mind may just be what we are conscious of and therefore in control of. Left unbeknownst, is if the mind makes a decision that leads to suppression of pain since the brain does. That is, a thought in the mind could transform into an action potential in the brain, which could then be sent down the spine to close the gate and inhibit the pain signals from coming through. There is no evidence for this kind of connection of the mind to the brain. However, this does not mean that the mind is not interconnected with the body and can affect certain feelings and sensations.

Previous studies on the other hand, provide us with clues to psychologically induced pain. For instance, Seligman and Buchanan at the University of Pennsylvania, found that those who were psychologically distressed had higher levels of chronic pain than those who were less distressed (5). Such findings would suggest that one's mind can influence the receptivity to pain. Perhaps the mind-body/brain problem, how mental processes affect the physical, is a similar way of saying that the mind controls the spinal gate. Perhaps the more one is in control of his pain, the less pain he has because his conscious mind communicates with the nervous system to close the gate. The hypnosis study, however, refutes the notion that the mind has power over pain since the subjects were unconscious while perceiving pain. Science has observed and supported the theory that the brain is involved in receptivity and activation of pain or the perception of pain, and that in fact may suppress pain. Indeed however, the power of positive thinking is more accepted, and supports the mind-body connection and is seemingly demonstrative of being in control of his ability to perceive or not perceive pain. Alas, there is no evidence that the mind controls the opening and closing of this spinal cord gate.

The truth of the matter, is that we will never really know what makes one "tougher" than another. All people are different and therefore their perceptions are different. This difference may be due to the fact that we each have different brains and perceive pain with more or less aversiveness than others do. There is strong scientific evidence in the study of pain supporting that certain brain parts are activated during painful stimuli and more interestingly, active during the aversiveness to pain. There are also meaningful observations suggesting the brain mediates the suppression of pain. This view of pain, we must remember is dependent on the notion that pain is a perception. Pain as a perception leaves the window open for discussion on the mind-body problem. If pain is one's own perception of a stimulus, then it follows that the mind may have conscious control of these perceptions. The scientific world is for the most part confident that the brain is involved in pain, in both suppressing it and receiving it. Still controversial, is which regions of the brain are in control of certain metacognitions of pain, such as perception and understanding. Especially one sided, is if the conscious self, the mind, can alter the nervous system and thus the perception of pain. Let it be known that there is still plenty of room for more observations and conclusions. In addition, we must note that this is also a very limited view of pain. For example, the body's endogenous opioid system was left out despite the increasing well supported belief that endorphins suppress pain as well. It is important to bear in mind that the brain has a role in allowing pain in and out through the theorized spinal gate. However, it is also worthwhile to consider the possibility that one's entire perception of pain may be conscious in origin and simply correlate to the mechanisms of the brain, rather than stem from just the brain entirely.


1) 1)Pain Anatomy

2) 2)The Human Perception of Pain

3) 3)Brain Pain Pathways

4) 4)Modification of pain within the spinal cord

5) 5)The Skeptics Dictionary

6) 6)Mind and Body Interactions

7) 7)Mind-Body-Medicine

8) 8)Mind and Body Wellness

9) 9) Carlson, Neil R., Physiology of Behavior. Needham Heights: A Pearson Education Company, 2001.

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