Scientists identify neurons that can dampen pain from touch
Researchers at Boston Children's Hospital have found a mind-body pathway to treat neuropathic pain, a difficult-to-treat type of chronic pain due to damage to the nervous system.
The study published on Wednesday in the journal Nature demonstrated that neurons which originated in the brain's cortex influence sensitivity to touch. It explained why mind-body techniques to control pain seemed to help many people.
"We know that mental activities of the higher brain -- cognition, memory, fear, anxiety -- can cause you to feel more or less pain," said Clifford Woolf at Boston Children's. "Now we've confirmed a physiological pathway that may be responsible for the extent of the pain. We have identified a volume control in the brain for pain -- now we need to learn how to switch it off."
Pain sensation was previously believed to originate with neurons in the spinal cord receiving sensory information from the body and relaying it on to the brain. The new study found that a small group of neurons in the cortex can amplify touch sensation, sending projections to the same parts of the spinal cord that receive tactile sensory information from the body.
"The anatomy of this circuit has been known for some time, but no one actually looked at its function before," said He Zhigang from Boston Children's who led the study.
In normal conditions, the touch and pain layers of the spinal cord are strongly separated by inhibitory neurons, but after nerve injury, the inhibition is lost, leading to touch information activating pain neurons, according to the study.
They suggested that these cortical neurons could be a potential target for treating the tactile component of neuropathic pain, via drugs or possibly brain electrical stimulation, breaking a feedback loop that introduced and exaggerated the pain response to normally non-painful touch.
When the team severed these neurons or silenced them genetically in a mouse model of neuropathic pain, the mice stopped recoiling from light, innocuous touches, such as stroking with a soft paintbrush or placement of a bit of tape on the bottom of a foot.
But the mice retained their sensitivity to truly painful stimuli, reflexively withdrawing their paws when exposed to heat, cold or pinpricks, according to the study.