Pain is the body’s protective mechanism and a complex neurological phenomenon. Moreover, ongoing pain in the sense of chronic pain can be a disease. Scientists from Technische Universität München (TUM) have now demonstrated that already during a few minutes of ongoing pain, the underlying brain activity changes by shifting from sensory to emotional processes. The opensource study is published in the journal Cerebral Cortex.
In the current study the team investigated pain perception, they wanted to investigate how the duration of pain or the action of a placebo affect activities in the brain. For their measurements they used electroencephalograms (EEGs). The test subject wore a cap with 64 electrodes that can measure nerve cell activity in the brain throughout the experiment. This method makes it possible to chronologically pinpoint which signals nerve cells use to respond to a pain stimulus.
In the current study 41 participants were given painful heat stimuli to the hand for ten minutes which varied in intensity throughout the duration of the experiment. The participants 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.
The team state that after just a few minutes the subjective perception of pain changed according to the participants. For example, the subjects felt changes in pain when the objective stimulus remained unchanged with the sensation of pain became detached from the objective stimulus after just a few minutes.
Previous studies showed that brief pain stimuli are predominantly processed by sensory areas of the brain that process the signals from the sensory organs such as the skin. However, in the current study with longer-lasting ongoing pain, the EEGs gave the scientists a different picture, in this case, emotional areas of the brain became active. The team observed that 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.
A second experiment in the study showed that it is not just the duration, but also the anticipation of a pain stimulus that affects perception. Twenty participants were initially given different intensities of painful laser pulses on two areas of the back of the hand. The participants then rated verbally how strong they perceived the pain stimuli. As the experiments progressed, the subjects were once again given the same stimuli, the difference this time being that two creams had previously been applied to both areas. Although neither cream contained an active substance, the subjects were told that one of the creams had a pain-relieving 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. The scientists were further able to demonstrate how the brain implements this placebo effect, although the subjects were given the same pain stimuli, the nerve cells in the second experiment triggered a different pattern of brain activity.
The team summise that the results show how differently the human 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.