An American study has shown that neurons in the sensory cortex of the brain influence the sensitivity to touch. Explanation.
A study by the Boston Children's Hospital and the National Institute of Mental Health (NIMH) could open new possibilities for the treatment of neuropathic pain. This type of chronic pain is difficult to treat, especially because of damage to the nervous system, which can make even the slightest touch extremely painful.
In their report, scientists, led by Zhi Gang and Clifford Woolf (Boston Children's F.M. Kirby Neurobiology Center), demonstrate that neurons that originate in the brain's cortex influence the sensitivity of the touch. This circuit could help explain why "mind-body techniques" designed to control pain help many people.
A control of the volume of the pain in the brain
"We know that the mental activities of the upper brain - cognition, memory, fear, anxiety - can cause more or less pain," argues Clifford Woolf. "We have now confirmed a physiological pathway that could be responsible for the magnitude of the pain, we have identified a control of the volume of pain in the brain, and now we have to learn how to extinguish it."
Previously, it was thought that the sensation of pain came from the neurons of the spinal cord, which received sensory information from the body and transmitted it to the brain. This new study revealed that a small group of neurons in the cortex can amplify the tactile sensation, sending projections to the same parts of the spinal cord, which receive tactile sensory information from the body.
"The anatomy of this circuit has been known for a while, but no one had ever looked at it before," says Clifford Woolf.
"Under normal conditions, the tactile and painful layers of the spinal cord are strongly separated by inhibitory neurons", describes Alban Latremoliere, co-author of the research. "After nerve damage, this inhibition is lost, leading to tactile information activating the neurons of pain.When the neurons of the spine, which are supposed to be painful, send this information to the brain, we feel the pain. "
Break the chain of reactions
The team believes that the cortical neurons it has identified may be a potential target for the treatment of the tactile component of neuropathic pain, via drugs or cerebral electrical stimulation. The goal would be to break the chain of reactions that introduces and exaggerates the response of pain to normally painless touch.
When the team turned off these neurons, the test mice stopped moving backwards with soft contact, such as stroking a brush on a paw. Animals, on the other hand, maintained their sensitivity to truly painful stimuli by removing their legs when exposed to heat, cold, or pinpricks.
"We now have the ability to silence or activate whole groups of neurons and imagine their electrical ignition patterns with single-neuron resolution, none of which was possible 10 years ago." , concludes Clifford Woolf.