Why does pain exist, how does it work, what can go wrong and how is it treated?

My name is Dr. Ewan St. John Smith. I'm a reader in Nociception in the Department of Pharmacology in the University of Cambridge, and today we'll be talking about: why does pain exist? How does it work? What can go wrong and how is it treated?

So, the talk will be split into four parts. We'll look at, firstly, what pain really is and how it works. Obviously, there could be a lot of detail here to go into, but we're just going to give an overview of how the system is setup. Then, we'll look at why does pain exists because some people think that a life without pain would be far simpler. Then, we'll look at what can go wrong with pain. We all know what pain feels like, but there are symptoms and syndromes that are particularly bad. In the last part, we will look at how pain is treated. Again, there are lots of different treatments currently available, some being in trials, still. We're just going to cover some of the main treatments that are used. So, let's begin then by looking at: what is pain and how does it work?

So, in terms of what is pain, internationally there are scientists, clinicians, nurses, physios, and so on that work on pain, and if we're going to have this word, we need to have an agreement about what is really meant by pain. So, for this, the International Association for the Study of Pain, which are taxonomy committee, they have defined pain as follows: an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Most people think of just the unpleasant sensory nature of pain. If you pick up a hot cup of coffee that's too hot you go ouch, you put it down again. We don't think of it being an emotional experience. We'll come back to what that really is in a second. So, a hot coffee cup that's associated with actual or potential tissue damage. If you don't put the hot coffee cup down, you'll injure your tissues. In terms of describing such damage, we need that part in there to take into account, for example, people who have phantom limb pain. These could be individuals who've had a limb amputated, and then complained about pain in parts of the body they no longer have. So, either this could be all in the brain and they're making it up, or there could be a good biological explanation for why they're complaining of pain in parts of the body that's no longer there. We now know there is a good biological explanation. Things are complicated. We know the pain is real, and that's why I have to have it described in terms of such damage. Symptoms are emotional experiences that lots of people don't think about. We need to look another word as well, and that word is nociception. This is a neural process of encoding noxious stimulus, noxious something, unpleasant and this is the nerve process. Going back to our coffee cup example, if I pick up a hot cup of coffee and it's too hot, my nerve will be activated by the noxious stimulus, the heat. That neural processes will send the signal to my central nervous system, and I respond by putting the hot coffee cup down. What I learned from that is that hot coffee cups are something I shouldn't pick up very easily, and I should have to wait longer for my coffee to cool down before picking up a mug. So, it's a protective function. But, there is no emotional component. I don't walk away from a cup of coffee, and get anxious about ever touching a cup of coffee ever again. By contrast, if we consider someone who is living with a chronic pain syndrome, for example, osteoarthritis; this person may be experiencing pain in many of their joints, let's say both knee joints, so everything they do causes some discomfort and pain. Walking is painful. Getting out of bed is painful. Therefore, these people become anxious because everything they're doing is making them feel worse. In turn, they are also not able to live their previously normally active lives to the same extent. Life can be quite depressing if you're not able to live it to what the extent you would wish to. Therefore, we can have this negative emotional experience. So, pain, in its truest form, encompasses both sensory and an emotional component. Indeed, we can look at people experiencing chronic pain and observe; there are much higher levels of anxiety and depression in this population than in a non-pain population. Also, preclinical research uses rodent models of pain; and really, here, we're measuring nociception, because we can't communicate to the rodent the same way as you can with a human. We could infer that the rodents might be depressed because it's not an active today as it was yesterday, but we don't know for sure. So, pain scientists like myself working with preclinical models with pain, often use the words nociception and pain interchangeably. Really, when we're studying pain, we're quite often studying nociception. We're measuring how an animal's behavior changes in response to a stimulus, so measuring nociception, from that we can infer things about pain. So, if we think about nociception and pain, we need to put these in a bigger context of how the sensory nervous system works. In the 1600s,