Pain on the Brain

            The nervous system has so many different tasks to do every day that it is a wonder that there are not more mishaps in the day-to-day function of humans.  Despite the fact that overall, our nervous systems allow us to make it through everyday without falling over or running into things, there are cases where somewhere wires get crossed and the usual predicted outcomes do not occur.  One of the easiest examples to observe is anything to do with sensory input, because so many different things in our environment go into a single experience every instant of our lives.  There are people with synesthesia who associate smells, tastes, or colors with certain words, or other kinds of sensory recombinations.  Another interesting example is that of how pain is experienced and interpreted by the nervous system.  As I thought about this function of the nervous system in relation to other senses, the phrase “blinding pain” entered my thoughts and would not go away.  I began a search of this phrase that does not really make sense upon further thought but is used so frequently in common discourse.

            I searched through psychological and biological journals as well as the internet as a whole for academic reference to “blinding pain”.  I could not find anything that described what exactly this meant, despite the fact that it was used to describe pain experienced by patients and study subjects.  I began to wonder where this phrase came from.  Obviously pain cannot cause a person to lose their sight on its own.  Pain might be caused by some medical problem that also affects the eyes, but the pain itself is not responsible for that.  I found this slightly distressing as it made no sense to me that this phrase is commonly accepted, but has no literal basis.  I presented my problem to fellow students, and we discussed the meaning behind “blinding pain”.

            After discussion, we came to the conclusion that the “blinding” refers not literally to affects on sight, but to the sensory system as a whole.  This makes more sense, in that if a person experiences intense pain, their nervous system cannot process other things because it is in sensory overload with whatever is causing the pain.  There are many definitions of blind that make the case for this explanation even stronger: 1) unwilling or unable to perceive or understand, 2) lacking all consciousness or awareness, 3) to deprive of discernment, reason, or judgment, 4) without guidance or forethought, 5) to an extreme or absolute degree; completely (1).  These various definitions further helped to convince me that “blinding pain” refers to a pain so intense that the brain can only process information to do with the pain, causing the rest of the sensory system to go “blind” until the pain is eased.  Thinking back to times of when I was in great pain, I realized that it is indeed true that in cases of severe pain, I remember not being able to really think about anything else for very long.

            Once this conundrum was more or less resolved to my satisfaction, some new questions arose.  Why is it that sometimes you can cut yourself and not know it, until you happen to see the wound, and then all of a sudden it starts to hurt?  Why should seeing an injury make a difference in the function of pain receptors? And why is it that this only occurs some of the time?  In my search for answers to these new questions I came across the account of a woman with chronic back pain who became involved in a study in which the subjects attempted to control their pain by watching their real-time brain functions on an fMRI screen (2).  While this was not exactly what I was looking for, it was related and intrigued me so I pursued this avenue of investigation.

            The study was conducted by Christopher deCharms, a neuroscientist, and Sean Mackey of Stanford University’s Pain Management Division.  For the woman with chronic back pain, the goal was for her to watch the parts of her brain that were activated during her pain (the anterior cingulate cortex and the insula) on a real-time fMRI and to use that visual to try and change the activity in those areas to control her pain (2).  The general idea is that the ability to control specific brain activity is like strengthening any muscle in your body.  The subjects practice concentrating on reducing the visible activity in their brains until they have more control over it, which is an example of the brain’s ability to change, which is also called neuro-plasticity (2). 

            The eight subjects of the study were put through three training runs of thirteen minutes each to practice increasing and decreasing their pain intensity to a stimulus.  The subjects were given strategies to help increase the pain (such as imagining the area was burning) as well as to help decrease the pain (such as imagining they were infusing a painkiller directly onto the area).  The first training run, the subjects felt no difference in intensity whether they were focusing on increasing or decreasing their pain.  By the last run however, the subjects reported higher pain intensities when they were focusing on increasing the brain activity in the areas responsible for pain, and they reported less pain intensity during the times when they were focusing on decreasing the brain activity (3).  The experimental group had greater changes in pain intensity than any of the four control groups (group 1 had extended practice but no training with the real-time fMRI, group 2 had double the amount of time of training for focusing attention away from the pain, group 3 had training with the real-time fMRI, but from an area of the brain not related to pain, and group 4 had real-time fMRI training but with an MRI taken from another subject) (3).  The study also had eight subjects who suffered from chronic pain go through the training and the experiment with no extra pain stimulus and they reported decreases in their baseline pain levels when they focused on decreasing the activity in the pain areas of the brain.  These subjects reported a decrease in pain by 44%-64%, which was up to three times as much as the control groups (3).

            While my original questions on how visual input affects pain perception, were not clearly answered anywhere in my research, this study on fMRI training to reduce pain still showed that there is a significant link between pain and other sensory input, in this case, it is visual.  It seems that perhaps the situation of not having an injury hurt until one sees it could be interpreted as the brain having an untrained response that is similar to the trained responses of the study subjects.  Those people were able to eventually increase or decrease brain activity in pain areas, allowing them to have a measure of control over their pain experience.  So perhaps when a person suddenly feels pain when they see a cut for the first time, it hurts so much because the added visual input increases their brain activity in pain areas.  If a person went through training to learn how to decrease that activity, then perhaps upon seeing an injury one did not know they had, after the initial increase in activity, one could put into practice the training and in fact decrease their pain even though they are now aware of the injury.  I find it comforting to know that after all the evidence that points to the fact that humans might not have very much control over what they do, that this seems to point in the opposite direction, giving us hope that we have some form of control over our experiences.

WWW Sources

1)      http://www.dictionary.com; online dictionary resource

2)      http://www.technologyreview.com/Biotech/17058/; personal story on website, technology review by MIT

 3)   http://www.pnas.org/cgi/content/full/102/51/18626?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=1&author1=deCharms%2C+Christopher&author2=Mackey% 2C+Sean&andorexacttitle=and&andorexacttitleabs=and&andorexactfulltext=and&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT; “Control over brain activation and pain learned by using real-time functional MRI”, online journal of the Proceedings of the National Academy of Sciences of the United States of America.