It’s sometimes hard to imagine pain as a good thing but it is. Short, sudden pain signals trauma and commands action: quickly escape whatever it is that’s causing the pain. Pain that lasts longer than a warning signal can be exhausting and cause one’s mood to be less than hospitable sometimes. There’s a reason for that. A new study indicates the brain processes pain in different ways: short, sudden pain is processed as a physical sensation but chronic, long-term pain is processed in the brain’s emotion-processing areas.
Professor Markus Ploner, a professor of human pain research at the Technische Universität München in Munich, Germany, enlisted 41 volunteers to test his theory that long-term pain is felt emotionally rather than physically. Volunteers were all healthy young adults, 20 to 32 years of age. Twenty-two were women.
To record their brain activity during experiments, each study participant was fitted with a 64-point electrode cap which produced an electroencephalogram (EEG) of activity at 64 points of the brain. One hand of each volunteer served as the site of the stimulus the EEG would record. With their other hand, they were instructed to gauge the pain throughout the course of each experiment. Pain was measured on a scale of zero (no pain) to 100 (worst tolerable pain). Unbeknownst to the volunteers, stimulus intensity never went higher than the individual’s tolerance for pain at their own self-determined 70 mark on the scale.
10-Minute Tonic (Slow) Experiment
A steady degree of heat was applied to the test hand of each participant for 10 minutes. They adjusted the scale according to pain intensity. Their EEG readings indicated that pain at the beginning of the experiment was processed in the sensory areas of the brain, where signals from the senses, including touch, are processed.
As the stimulus continued, brain activity changed, with the emotional processing areas becoming active and the sensory areas returning to a resting stage.
Pain Anticipation and Placebo Effect Experiment
In a second experiment, 20 volunteers were subjected to pulses of pain-causing stimulation on the backs of one hand. They verbally rated the pain using the 0-to-100 scale.
After multiple rounds of pulsating stimulation, the researchers applied two creams to the volunteers’ hands; the creams were described as pain-relieving ointments although neither cream actually contained any active ingredients.
The pain ratings were lower after the creams were applied although the intensity of the stimulus was the same as it had been before the creams were applied.
The EEG readings revealed the anticipation of pain triggered activity in areas of the brain different than the areas that process sudden onset of pain. The EEGs also revealed activity in different areas of the brain before and after application of the placebo creams.
“Our results show how differently our brain processes the same pain stimuli,” said Ploner. His brain mapping experiments demonstrate how complex and challenging it is to treat chronic pain but EEG mapping “is absolutely essential for improving therapeutic options for pain patients.”
- Ploner, Markus, et al. "Prefrontal Gamma Oscillations Encode Tonic Pain in Humans." Cerebral Cortex. Oxford University Press, 8 Mar. 2015. Oxford Index. Web. 18 Mar. 2015.