Scientists inflict tennis elbow in the name of science
Volunteers were deliberately inflicted with elbow pain in an experiment that tries to understand the causes of chronic pain.
One in ten of us will be diagnosed with chronic pain this year, yet scientists have no clear answer as to how and why chronic pain develops.
Now, a team of scientists believe they have found an important piece of the puzzle. By giving a group of healthy subjects temporary tennis elbow, they have mapped how muscle pain in the elbow affects one part of the brain.
"The area of the brain that controls a painful muscle expands when you've had pain for a long time. This makes it hard for the brain to control the muscles,” says co-author Professor Thomas Graven-Nielsen from the Center for Neuroplasticity and Pain (CNAP) at Aalborg University, Denmark.
“This can lead to persistent pain over time as it causes other muscles to become overworked," he says.
Areas of the brain expand
A series of healthy volunteers took part in an experiment where they received an injection to the elbow which induced a harmless elbow pain for a few days.
The scientists then measured the parts of the brain responsible for activating the painful muscle around the elbow.
After four days, they could see that the area of the brain had significantly expanded, and the muscle nervous system had reorganised itself.
"Basically it's the first time anyone has shown that pain causes the muscle nervous system to reorganise itself over time. Before it has been thought that it took much longer before these changes in the brain happened, but our experiment shows that it only takes a few days," says Graven-Nielsen.
The brain is like plastic
The brain is a flexible instrument, allowing certain areas to expand and reorganise its ability to control these painful muscles.
Graven-Nielsen compares it to bending a piece of plastic. If you bend it a little over a short period, the plastic will return to its original shape. But bending it hard enough and long enough may be change its shape forever.
Clinical Professor Troels Staehelin Jensen from the Danish Pain Research Center at the University of Aarhus says it is important to see if the results of the study can be replicated in a group of people already suffering from chronic pain.
"It’d be interesting to see if this pain adaptation in the brain also occurs in people living with a pre-existing pain condition. I think we must try to see if the results are repeated when studying a chronic pain condition," says Jensen.
Graven-Nielsen admits that the results do not provide the definitive explanation of why the pain is persistent. He believes, however, that the discovery could nudge scientists closer to this goal.
"We do not yet know what why some patients only experience temporary pains, while others feel it more permanently, but we know that the plasticity effect plays a role," he says.
Translated by: Catherine Jex
- 'Motor Cortex Reorganization and Impaired Function in the Transition to Sustained Muscle Pain', 2015, Cerebral Cortex, DOI: 10.1093/cercor/bhu319