How differently do we perceive pain? And how does the duration of pain – or a placebo – affect our brain activities? Scientists have taken a look inside the human brain and shown that after just a few minutes of ongoing pain, the underlying brain activity shifts from sensory to emotional processes.
A momentary lapse of concentration is all it takes for a finger to become trapped, to receive a bump on the head or sprain an ankle – and it hurts. Pain is the body’s indispensable protective mechanism, and at the same time, a complex neurological phenomenon that’s affected by a number of factors. Ongoing pain in the sense of chronic pain can even be a disease in its own right.
A team of scientists from the Technische Universität München (TUM) has put pain perception to the test and uncovered how the duration of pain or the action of a placebo affects activities in the brain.
Pain influences emotion
The researchers used electroencephalograms (EEGs) to chronologically pinpoint which signals nerve cells use to respond to a pain stimulus. Volunteer test subjects wore a cap with 64 electrodes that measured nerve cell activity in the brain throughout the experiment.
The 41 study participants were given painful heat stimuli to the hand over a period of ten minutes, with varying intensity during 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.
“We were absolutely amazed by the results,” says neuroscience expert Markus Ploner, who spearheaded the research.
“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.”
Previous studies have shown 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. But in this experiment with longer-lasting pain, the EEGs gave the scientists a different picture: in this case, 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,” explains Ploner. “This realisation is extremely interesting for the diagnosis and treatment of chronic pain where pain persists for months and years.”
Placebos change the perception of pain
A second experiment showed that it’s not just the duration, but also the anticipation of a pain stimulus that affects perception. Twenty test subjects 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 both creams were placebos – lacking any active substance – the subjects were told that one of the creams had a pain-relieving effect.
And the result? “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,” Ploner says. The scientists were 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 run 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,” says Ploner.
Adapted from article by Vera Siegler, TUM Research News