Where's Your Pain? New Insights Into How The Brain Processes Pain Location

Spatial aspects of pain are a common problem in diagnosis, said Robert Coghill, Ph.D., senior researcher on the study and a neuroscientist at Wake Forest University School of Medicine. Patients cannot always distinguish pain from indigestion and pain from a heart attack, for example. Pain from a nerve injury is often felt at sites other than at the injury. And, in some cases, an injury on one side of the body results in pain on both sides.

"The scientific understanding of spatial aspects of pain is so limited that patients with widespread pain may get sent to a psychiatrist rather than a pain clinic," said Coghill.

"This study expands our notion of where in the brain the 'where' component of pain is processed -- it's not as simple as we thought," said Coghill. "Brain mechanisms that process the location of pain now appear to be highly similar to those that process the location for hearing and vision."

The new finding published this week in the Journal of Neuroscience -- that multiple regions of the brain are involved in determining pain location -- was achieved with functional magnetic resonance imaging (MRI), a technique that shows brain activity while a task is being performed.

The study involved 12 healthy volunteers from ages 22 to 39. Two thermal stimulators were placed between 1.5 and 6 inches apart on each participant's lower leg. While participants were undergoing a functional MRI, one of the stimulators was activated at a temperature between 95 and 120 degrees. Then, after a 30-second rest period, one of stimulators was activated. Participants were told to push a button to indicate whether the second activation was in the same or a different location from the first.

According to conventional wisdom, a few brain regions, including the primary somatosensory cortex, are involved in determining pain location, said lead author Yoshitetsu Oshiro, M.D., Ph.D. But the MRI testing showed that other areas, known as the medial pain system and thought to be involved in the emotional aspects of pain, were also used.

"This was very surprising," said Oshiro. "Pain isn't well understood and better treatments are needed. This shift in direction will be important to move research and treatments in the right direction."

Coghill agreed. "A whole network of brain areas were lighting up while subjects were evaluating the spatial location of the stimulus," he said. "We're showing something very new and different: areas thought historically to be involved in processing the emotional aspects of pain were involved in determining pain location. It gives us a whole new conceptual framework for thinking about spatial aspects of pain."

He said the study suggests that a lot of our sensory experiences are built by comparing incoming information with previously experienced information. "That convergence of information gives us a full sensory experience of the information coming in from our nervous systems."

The study was funded by the National Institutes of Health.

Other researchers were Alexandre Quevedo, D.D.S., John McHaffie, Ph.D., Robert Kraft, Ph.D., all from Wake Forest.