Chronic Pain Alters DNA

The team of researchers led by Prof. Laura Stone at McGill University recently found that 6 months after inflicting nerve injuries on mice, the mice still displayed signs of skin hypersensitivity and motor impairment. This was associated with epigenetic changes in the amygdala and prefrontal cortex of the brain. Epigenetics explains how genes can be switched on and off. It’s the study of mechanisms by which the environment controls gene activity. Interestingly, the DNA changes were reversed by placing the mice in a more stimulating environment (three mice per cage, a running wheel mounted on a plastic hut and marbles). Whereas, placing the mice in an impoverished environment (one mouse per cage in the absence of a running wheel, marbles or any other forms of enrichment) didn’t restore normal DNA. DNA changes were found to correlate to hypersensitivity. In other words, placing the mice in a stimulating environment helped decrease their pain.

Long-term Use Of Opioids Lowers Testosterone Levels

A recent study by Rubinstein et al. published in The Clinical Journal of Pain has shown that long-term use of opioid painkillers by men is associated with lower levels of testosterone. This effect is much more prevalent when using long-acting opioids. Low testosterone or hypogonadism, as it’s also known, has been linked with decreases in muscle mass, bone density, cognition, mood, sex drive and general quality of life.

Pain And Emotion

Although mainly about the effects of emotion on reason, ‘Descartes’ Error‘ by Antonio Damasio contains a few fascinating nuggets on pain. He distinguishes 2 components to pain:

• Sensory perception from skin, mucosa, muscle, organ, etc. – the nerve endings stimulated in an area of the body lead to a ‘pain image’, a temporary representation  of body change in the brain. This is no different from any other kind of body perception and if it were all, we would not be inconvenienced.
• Emotion and feeling – it’s from these body-state changes that the unpleasant feeling of suffering is formed. “Suffering puts us on notice and offers us the best protection for survival, since it increases the probability that individuals will heed pain signals and act to avert their source or correct their consequences.“

Damasio’s views on emotion/feeling and pain are probably the result of his experience with the eminent Portuguese neurosurgeon Almeida Lima. Lima worked closely with Portuguese neurologist Egas Moniz. Together they developed prefrontal leucotomies, later known as lobotomies, during the 1930s. In 1949 Moniz received the Nobel Prize in medicine for his work. Damasio recalls following Lima on a pre-operative visit of a patient with trigeminal neuralgia, a condition that causes severe facial pain. “He was crouched in profound suffering, almost immobile, afraid of triggering further pain. Two days after the operation, when Lima and I visited on rounds, he was a different person. He looked relaxed, like anyone else, and was happily absorbed in a game of cards with a companion in his hospital room. Lima asked him about the pain. The man looked up and said cheerfully “Oh, the pains are the same, but I feel fine now, thank you.” Clearly, what the operation seemed to have done, then, was abolish the emotional reaction that is part of what we call pain. It had ended the man’s suffering.”

Obviously, lobotomies are extreme measures and they can cause serious side effects. This is certainly the reason fewer and fewer operations are being performed. Nowadays these operations are called psychosurgery and they have become much more precise. The important point is Damasio’s view on the link between pain and emotion. It corroborates a lot of the research being done on chronic pain. Hence, the importance of addressing the emotional part. Fortunately, there are now safer more humane ways of doing it, like relaxation, meditation, cognitive behavioural therapy, neuro-linguistic programming and hypnosis.

Mindfulness Changes Pain

I read an interesting passage in ‘Mindfulness’, Ellen Langer’s insightful book on social psychology.

“Patients are often certain that pain is inevitable in a hospital. Caught in such a mindset, they assume that, without the help of medication, pain cannot be controlled. In our experiment, we tried to learn whether people could control their experience of pain by putting it in a different, more optimistic context.

Patients who were about to undergo major surgery were taught to imagine themselves in one of two situations: playing football or preparing for a dinner party. In the midst of a rough skirmish on the football field, bruises are hardly noticed. Similarly, cutting oneself while rushing to prepare dinner for ten people who will be arriving any minute might also be something one would hardly notice. In contrast, a paper cut suffered whilst reading a dull magazine article quickly becomes the focus of attention. Through examples of this sort, participants in the study were taught that, rather than being inevitable, much pain we experience appears to be context-dependent.

Hospital staff, unaware of our hypothesis, monitored the use of medication and the length of stay for the participating patients in the experimental group and in the control groups. Those patients who were taught to reinterpret the hospital experience in nonthreatening ways took fewer pain relievers and sedatives and tended to leave the hospital sooner than the untrained patients. The same hospital experience seen through psychologically different eyes is not the same experience, and the difference could be measured in lower doses of medication and quicker recoveries. This reappraisal technique effectively loosened the hospital mindset and, by showing that pain was not a certainty, gave the participants more control over their convalescence.”

This experiment clearly demonstrates that changing our mindset can change our experience of pain!

Chronic Pain And Emotion

Professor Apkarian has studied chronic pain for over 20 years. In a recent study looking into people with recent back pain, he was able to predict with 85% accuracy those that would go on to develop chronic back pain! How? By noticing an increased level of cross-talk between two specific parts of the brain…suggesting that the more emotionally the brain reacts to the injury…the greater the likelihood of developing chronic pain. The researchers also found that the subjects that developed chronic back pain lost grey matter density…this is in accord with earlier studies that have measured brain atrophy in people with chronic pain. These changes can be compared to those that occur with aging.

BBC Horizon’s Secret World Of Pain

Last year BBC Horizon created a documentary entitled ‘The Secret World of Pain‘. I watched it on YouTube a week ago, thought it was really well put together and so decided to share the most salient points.

Pain is one of our most ancient survival mechanisms and it protects and alerts us to danger. The SCN9A gene is responsible for regulating electrical signals that send pain sensation to the brain. Certain rare genetic disorders can prevent people from feeling pain…these unfortunate people are much more susceptible to burns and other injuries…this underlines just how crucial the sensation of pain is to us.

Pain can alert us to injury or potential injury, but why doesn’t it reflect the extent of injury…and why is it so subjective? There are a couple of possible reasons for this. Key experiences in early life have been found to be as important to pain perception as genetics. Early life is crucial for the formation of pain pathways which are shaped in response to touch. For example, premature babies are exposed to a lot more painful procedures and this alters the normal development of their pain pathways…the overdevelopment of pain pathways makes them hypersensitive and much more likely to experience pain in the future.

Pain and pleasure are both perceptions…psychological constructs…and so environment, context, decision-making, attention, distraction, motivation, emotion, etc can change how signals are processed and hence influence pain. There is a limit to how much information the brain can process at any one time…focussing attention on something pleasant (distraction) decreases the brain’s ability to process pain signals.

Subjects in an experiment were shown a triangle and exposed to a low temperature which they rated as 3/10 on a pain scale…this was repeated several times…they were then shown a square and exposed to a high temperature which they rated as 7/10 on a pain scale…this was repeated several times…they were then shown the square but exposed to the low temperature instead…surprisingly they rated the pain as 5/10. The researchers concluded that anxiety had affected their sensation of pain. I would add that expectation and conditioning may also have played a part.

Chronic pain is pain that persists long after an injury has healed…and therefore serves no purpose. It affects 1 in 5 people and is one of the biggest medical health problems. It can become an enormous burden on the brain and leads to chemical and structural changes. MRI scanning has revealed that people with chronic pain have less grey matter in the pre-frontal cortex. The answer to chronic pain may lie in reversing these changes. Encouragingly, electromagnetic impulses to the brain cortex have helped to normalise changes and to decrease pain, albeit temporarily. Research into this sort of treatment is extremely promising but still in its infancy.

Pain: how much is in the mind?

A study by Luis Buenaver and colleagues published in the June edition of Pain has shown some fascinating links between pain, thinking and sleep. It’s already known that about 80% of people with chronic pain experience troubled sleep and that poor sleep increases pain sensitivity. It is also known that pain catastrophizing is a contributor to chronic pain. Catastrophizing is a combination of rumination and negative thinking. What Buenaver and his colleagues discovered was a direct link between pain catastrophizing, poor sleep and worsening pain…a vicious cycle…the more often you think negatively about your pain experience…the more your sleep is disrupted…the worse your pain becomes…which in turn adversely affects your thoughts, etc.

Another piece of research published in this month’s Current Biology by Christian Sprenger et al. demonstrates that mental distraction techniques can decrease pain sensations by inhibiting incoming pain signals in the spinal cord. The effect was found to be partly mediated by endorphins.

In essence, people with chronic pain can improve their sleep and comfort by choosing to focus on pleasant activities or goals rather than brood gloomily over their pain.

To change the way we feel we must change the way we think!

Pain And Perception

I read an interesting article in BBC News Health a couple of weeks ago. It reviewed 2 recent studies on pain. The first was published in The Journal of Pain by Atsuo Yoshino et al. Subjects were shocked with an electric current whilst they were shown pictures of sad, happy or neutral faces. Photos of an emotional face usually provoke the same emotional response in the person viewing the picture. Although the electrical stimulation was the same in all cases, subjects felt more pain when looking at sad faces.

The second study was conducted by Marion Hofle et al. in Pain. The researchers asked the subjects to place one of their hands under a screen. On the screen, they played a video of a hand being pricked by a needle, poked by a cotton bud or just left alone. The subjects perceived the hand on the screen as their own.  A painful or non-painful stimuli was applied simultaneously to the video. Viewing the needle prick increased the unpleasantness ratings of the stimulus.

As these studies have shown, negative emotional states and negative expectation seem to increase pain and so the mind plays an important role in the experience of pain. As a physiotherapist, dealing with pain is a daily occurrence and I can remember qualifying as an acupuncturist over 10 years ago…I was desperately keen to use my new skill on anyone that was willing to try and worked hard at convincing anyone that was hesitant to try! With those that were initially hesistant…possibly due to a slight needle aversion, I quickly noticed their exaggerated responses to acupuncture. I can remember several occasions when I would gently touch them with a finger or with the plastic guide tube that surrounds the needle and they would jump and shout “ouch”…to which I would reply “relax, we haven’t started yet!” I’ve now learnt from those experiences and no longer feel the need to convince everyone to have acupuncture…no matter how great I think it is!

John Milton was right in Paradise Lost…“The mind is its own place, and in itself can make a heaven of hell, a hell of heaven.”