Brain waves may help doctors to understand who is more susceptible to pain.
Pain is a strange phenomenon. How painful a particular injury is can differ from person to person, even if the wound is the same.
For instance, if we expect something to hurt, it is more likely to be painful than if we expect it to be painless.
Because pain is so varied, estimating how much pain a person may feel following a medical procedure is impossible to gauge.
Recently, scientists from the University of Birmingham in the United Kingdom teamed up with those from the University of Maryland in College Park. They looked for clues about pain sensitivity hidden in brain waves.
To investigate, they introduced capsaicin paste to the forearms of 21 participants. Capsaicin is the compound that gives chilies their heat and, when placed on the skin, it induces "robust thermal hyperalgesia."
In other words, it feels hot and painful. The participants endured the burn for 1 hour.
Before and during the exposure, the team assessed brain activity with an electroencephalogram (EEG). An EEG is a non-invasive test wherein small metal discs are attached to the scalp. These detect voltage fluctuations, giving a general picture of brain activity.
The scientists were particularly interested in a type of brain wave called alpha waves. Originating in the occipital lobe — or the visual processing area toward the back of the skull — alpha waves are more prominent when relaxing with closed eyes, and they are reduced with open eyes, when drowsy, and during sleep.
The results were fascinating. Alpha wave frequency appeared to predict pain sensitivity.
Participants whose alpha brain wave frequency was slower before the capsaicin was introduced reported feeling much more pain than those who had a faster frequency of alpha waves before.
Also, those whose alpha waves increased during the pain reported less pain than those whose alpha waves dropped off.
The implications for chronic pain
As co-senior study author Dr. Ali Mazaheri, from the University of Birmingham's Center for Human Brain Health, explains, "Here, we observe that an individual's alpha frequency can be used as a measure of an individual's predisposition to developing pain."
"This," he adds, "has a direct relevance to understanding what makes an individual prone to chronic pain after a medical intervention, such as surgery or chemotherapy."
Understanding which individuals might be more susceptible to pain could be very useful for the medical community. The findings were published recently in the journal Neuroimage.
"Potentially this means we could be able to identify which individuals are more likely to develop pain as a result of a medical procedure and take steps early on in formulating treatment strategies in patients likely to be predisposed to developing chronic pain."
Dr. Ali Mazaheri
Alpha waves have been implicated in pain perception before. According to Andrew Furman, of the University of Maryland, "Alpha frequency has been found to be slower in individuals who have experienced chronic pain."
"So," he continues, "the fact we observed that the slowing down of alpha activity as a result of pain correlated with the intensity of an individual's pain report was not that unexpected."
However, the fact that alpha waves might offer some predictive power is unexpected. Furman goes on, saying, "What was very surprising though, was that prior to the pain — that is, pain-free alpha frequency — [we] could predict how much pain individuals would experience."
"This would suggest," he adds, "that it could be that the slowing of alpha activity in the chronic pain patients isn't because of the pain, but rather these individuals had slow alpha frequency to begin with, and, as such, were more prone or vulnerable to developing pain."
Adding to our knowledge of this topic, these results will help to develop a better understanding of which individuals might be more susceptible to chronic pain. They may also help us to understand how pain works in the brain.