By Pat Anson, Editor
Many chronic pain sufferers resent being told their pain is “all in your head” or that they’re being too emotional about their pain.
But tests conducted by German researchers suggest that the human brain begins to shift from sensory to emotional processing of pain after just a few minutes of painful stimuli.
Scientists at Technische Universität München (TUM) in Munich enrolled 41 people in a study to measure brain activity as they were exposed to painful heat stimulation of a hand. Participants wore a cap with 64 electrodes that measured nerve cell activity in the brain throughout the experiment. The electroencephalograms (EEGs) made it possible to pinpoint which nerve cells respond to pain.
Participants were then given painful heat stimuli to the hand for ten minutes, with the intensity of the heat varying throughout the experiment. The test subjects were asked to continuously assess the level of their pain on a scale of one to a hundred with the other hand using a slider.
"We were absolutely amazed by the results. After just a few minutes, the subjective perception of pain changed. For example, the subjects felt changes in pain when the objective stimulus remained unchanged. The sensation of pain became detached from the objective stimulus after just a few minutes," said Markus Ploner, MD, a professor for human pain research at the TUM School of Medicine.
Previous studies have shown that brief pain stimulation is predominantly processed by sensory areas of the brain that process signals from nerves in the skin. However, in the heat experiment with longer-lasting pain, the EEGs showed that emotional areas of the brain became active.
"If pain persists over a prolonged period of time, the associated brain activity shows that it changes from a pure perception process to a more emotional process. This realization is extremely interesting for the diagnosis and treatment of chronic pain where pain persists for months and years," explained Ploner.
A second experiment showed that it is not just the duration, but also the anticipation of pain that affects perception. Twenty test subjects were given different intensities of painful laser pulses on two areas of the back of the hand. The participants then verbally rated how strong they perceived the pain to be.
In a second round of testing, the subjects were again given the same stimuli, but this time with two creams applied to both hand areas. Although neither cream contained an analgesic, the subjects were told that one of the creams had a pain-relieving effect.
Researchers found the cream had a placebo effect.
"The subjects assessed the pain on the skin area with the allegedly pain-relieving cream as significantly lower than on the other area of skin," said Ploner.
In addition to feeling less pain, the EEGs showed that nerve cells triggered a different pattern of brain activity.
"Our results show how differently our brain processes the same pain stimuli. Systematically mapping and better understanding this complex neurological phenomenon of 'pain' in the brain is a big challenge, but is absolutely essential for improving therapeutic options for pain patients," added Ploner.