Max
07-31-2008, 05:56 PM
How the brain is wired for pain
The winning entry for a competition that gives PhD students funded by the Medical Research Council the opportunity to explain the relevance of their research
Michael Lee
The Guardian (http://www.guardian.co.uk/theguardian),
Tuesday July 29 2008
Article history (http://sci.rutgers.edu/forum/) http://image.guim.co.uk/sys-images/Football/Pix/pictures/2008/07/28/ronaldo4.jpg Portuguese footballer Cristiano Ronaldo writhes in pain. Photograph: Daniel Dal Zennaro/EPA
You slip on ice and land heavily on your hand. The pain is instant. Soon, your wrist reddens and swells. It becomes painful to the touch. You rush to the A&E department of the nearest hospital and get an X-ray. Luckily, you haven't broken anything - merely sprained your wrist. It should get better in a few days. In the meantime, your wrist hurts and you wear a wrist guard to protect it from further strain. A week later, your wrist is back to normal. You soon forget that you were ever in pain.
What if the pain doesn't go away, though? Months pass. Your wrist gets worse. Now your whole hand hurts. Washing up and getting dressed become difficult. You start to worry and can't sleep properly. Doctors and painkillers become a part of your life. The pain is always there, but your doctor can't find anything wrong. No one quite understands. You feel depressed. People seem to think you're making a big fuss. Maybe the pain is all "in your head".
The initial injury might have been different, but this story will be familiar to many chronic pain patients. Their pain persists long after the injury is healed. Without any injury to protect, such pain serves no purpose, and becomes crippling. Chronic pain is more common than we think. About a fifth of the world's population is believed to suffer from chronic pain. In Europe, chronic pain accounts for nearly 500m lost working days and costs the European economy more than €34bn (£28bn) every year.
Patients with chronic pain often complain of pain in areas where doctors find very little physical injury. These patients also suffer from anxiety and depression, both of which complicate and contribute to pain. This makes the study of any one cause of chronic pain very difficult. To get around that difficulty, some researchers simulate the symptoms that chronic pain patients feel in otherwise healthy volunteers.
I use capsaicin to increase pain sensitivity temporarily in research volunteers. Capsaicin is a chemical that comes from the chilli pepper. When applied to the skin, it activates heat sensors found on nerve endings under the skin. These nerves generate signals that pass like electricity along a wire, up through the spinal cord and brainstem before entering the brain. As a result, pain is experienced. A large area of skin around the spot where capsaicin has been applied also becomes sensitive. More pain than usual is experienced when a pin pricks the skin. Even a gentle caress can be painful.
What causes this increased pain sensitivity? One theory is that the nervous activity caused by capsaicin or by real life injury is not just transmitted from the spinal cord to the brain, where it is felt as pain, but also changes the nerve circuits through which it passes. These circuits are rewired as amplifiers and increase nerve activity so that more pain is experienced.
Brain scans can help locate these pain-amplifying circuits. Functional magnetic resonance imaging is a type of brain scan used in research. FMRI detects changes in magnetic fields that are related to brain activity. The big advantage FMRI has over other types of brain scans is that it does not involve radiation. I used FMRI to scan the brains of research volunteers whose skin had been sensitised by capsaicin and found increased activity in their brainstems. So perhaps the brainstem is an area where nerves get rewired to amplify pain.
http://www.guardian.co.uk/education/2008/jul/29/research.highereducation
The winning entry for a competition that gives PhD students funded by the Medical Research Council the opportunity to explain the relevance of their research
Michael Lee
The Guardian (http://www.guardian.co.uk/theguardian),
Tuesday July 29 2008
Article history (http://sci.rutgers.edu/forum/) http://image.guim.co.uk/sys-images/Football/Pix/pictures/2008/07/28/ronaldo4.jpg Portuguese footballer Cristiano Ronaldo writhes in pain. Photograph: Daniel Dal Zennaro/EPA
You slip on ice and land heavily on your hand. The pain is instant. Soon, your wrist reddens and swells. It becomes painful to the touch. You rush to the A&E department of the nearest hospital and get an X-ray. Luckily, you haven't broken anything - merely sprained your wrist. It should get better in a few days. In the meantime, your wrist hurts and you wear a wrist guard to protect it from further strain. A week later, your wrist is back to normal. You soon forget that you were ever in pain.
What if the pain doesn't go away, though? Months pass. Your wrist gets worse. Now your whole hand hurts. Washing up and getting dressed become difficult. You start to worry and can't sleep properly. Doctors and painkillers become a part of your life. The pain is always there, but your doctor can't find anything wrong. No one quite understands. You feel depressed. People seem to think you're making a big fuss. Maybe the pain is all "in your head".
The initial injury might have been different, but this story will be familiar to many chronic pain patients. Their pain persists long after the injury is healed. Without any injury to protect, such pain serves no purpose, and becomes crippling. Chronic pain is more common than we think. About a fifth of the world's population is believed to suffer from chronic pain. In Europe, chronic pain accounts for nearly 500m lost working days and costs the European economy more than €34bn (£28bn) every year.
Patients with chronic pain often complain of pain in areas where doctors find very little physical injury. These patients also suffer from anxiety and depression, both of which complicate and contribute to pain. This makes the study of any one cause of chronic pain very difficult. To get around that difficulty, some researchers simulate the symptoms that chronic pain patients feel in otherwise healthy volunteers.
I use capsaicin to increase pain sensitivity temporarily in research volunteers. Capsaicin is a chemical that comes from the chilli pepper. When applied to the skin, it activates heat sensors found on nerve endings under the skin. These nerves generate signals that pass like electricity along a wire, up through the spinal cord and brainstem before entering the brain. As a result, pain is experienced. A large area of skin around the spot where capsaicin has been applied also becomes sensitive. More pain than usual is experienced when a pin pricks the skin. Even a gentle caress can be painful.
What causes this increased pain sensitivity? One theory is that the nervous activity caused by capsaicin or by real life injury is not just transmitted from the spinal cord to the brain, where it is felt as pain, but also changes the nerve circuits through which it passes. These circuits are rewired as amplifiers and increase nerve activity so that more pain is experienced.
Brain scans can help locate these pain-amplifying circuits. Functional magnetic resonance imaging is a type of brain scan used in research. FMRI detects changes in magnetic fields that are related to brain activity. The big advantage FMRI has over other types of brain scans is that it does not involve radiation. I used FMRI to scan the brains of research volunteers whose skin had been sensitised by capsaicin and found increased activity in their brainstems. So perhaps the brainstem is an area where nerves get rewired to amplify pain.
http://www.guardian.co.uk/education/2008/jul/29/research.highereducation