- Pain occurs when nerve cells detect damage and transmit signals to the brain for interpretation.
- Everyone feels pain differently, which makes it challenging for doctors to define and treat.
- A new study, using brain scans, has found that gamma oscillations — brain waves linked to pain perception — have different timing, frequency, and location in different people.
- This finding could lead to pain treatments based on these individual “pain fingerprints.”
People feel pain when nerve endings in the skin called nociceptors detect damage and transmit signals to the brain. The pain may be acute — sudden onset and usually short-lived and treatable by dealing with the source of the pain — or chronic, lasting for much longer and harder to treat.
But not everyone feels pain in the same way, and it can be hard for doctors to determine the severity of a person’s pain.
Often, they use a numerical scale, with the pain described from zero for no pain at all, to 10 for the worst pain imaginable. Other methods include:
- verbal descriptor scale — the doctor asks different descriptive questions to narrow down the type of pain
- brief pain inventory —a written questionnaire helps doctors judge the effect of a person’s pain and assess changes in pain to detect patterns
- McGill Pain Questionnaire (MPQ) — respondents choose from three major classes of word descriptors (sensory, affective, and evaluative) to specify subjective pain experience
- faces scale — this is mainly used for children; the doctor shows a range of expressive faces, from distressed to happy, which the child uses to indicate their pain levels.
However, all of these methods are subjective, depending on the individual’s perception of their pain.
Now, a study led by the University of Essex, United Kingdom, has used brain scans to assess gamma oscillations, which are linked to pain perception.
The researchers found that individuals show distinct gamma responses, which they refer to as “pain fingerprints.” They suggest this finding may allow tailored pain treatments directed by an individual’s gamma response.
The study is published in the Journal of Neurophysiology.
Pain gamma oscillations unique
Lead author Dr. Elia Valentini, a senior lecturer in the Department of Psychology and Centre for Brain Science, University of Essex, told Medical News Today:
“Past work indicated that the perception of pain may be mediated by these fast neural oscillations we call gamma. Our work demonstrates that, even if we feel the pain as similarly intense, some of us will display these gamma oscillations triggered by painful stimuli whereas others won’t.”
“In a nutshell, we suggest that gamma oscillations are not required for pain, but when present, they are a stable and replicable feature of the individual,” he added.
Brain waves measured
The researchers tested pain responses in 70 people. All those involved in the study were healthy and young, with a mean age of 24 years. The majority were male.
They recorded results from two different experiments. The first had 22 participants, the second 48.
In the first, participants were given repeated pain stimuli and touch stimuli to the back of the right hand on two occasions, two weeks apart. The pain stimulus was produced by a Tm:YAG laser. The participants scored both stimuli from zero to 10.
In the second experiment, participants received high- and low-intensity pain stimuli from an Nd:YAG laser. Each person received 80 high and 80 low-intensity stimuli. They were asked to rate them from zero for no pain to 100 for maximum tolerable pain.
In both experiments, participants wore an electrode cap during the stimuli to produce electroencephalogram (EEG) data from which the researchers analyzed the gamma responses.
Toward an objective measurement of pain
Dr. Vernon Williams, a sports neurologist, pain management specialist, and founding director of the Center for Sports Neurology and Pain Medicine at Cedars-Sinai Kerlan-Jobe Institute in Los Angeles, not involved in this study, explained to Medical News Today:
“Pain is defined as an unpleasant sensory and emotional experience associated with, or resembling that associated with actual or potential tissue damage. It is not a ‘sensation,’ it is an ‘experience’. As such, it is always personal and individual, and subjective. So, it is not surprising that the gamma oscillations vary significantly from person to person.”
Not only did the pattern of gamma oscillations differ between different individuals, but the researchers found that, for each individual doing the repeat experiment, the pattern remained constant.
Dr. Valentini explained: “Our work clearly demonstrates that there is a remarkable stability: Participants with high/no gamma activity and high/no pain ratings in the former recording had high/no gamma activity and high/no pain ratings two weeks later.”
According to Dr. Williams, this could be useful for pain management: “It is interesting that the findings are reproducible within an individual, and that may have future implications regarding objective measures of pain and objective measures to assess pain interventions/treatments — particularly in the short term.”
However, Dr. Valentini added a note of caution: “Our study highlights that the importance of gamma oscillations for pain processing may be highly overstated. [It] acts as a timely reminder that even when a strong group-level correlation is replicated by several studies we may still be fooled in drawing causal interpretations.”
Do the findings have clinical relevance?
“In a nutshell, we suggest that gamma oscillations are not required for pain, but when present, they are a stable and replicable feature of the individual,” said Dr. Valentini
Their findings could lead to more personalized pain management, as Dr. Valentini went on to explain: “Our work resonates with the idea of personalized medicine whereby clinicians may focus on the specific individual’s biological patterns as to achieve faster and better diagnosis or treatment.”
“Thus, whilst our findings have no immediate clinical implication, they pave the way to a more precise assessment of neural responses mediating the experience of pain,” he told us.
Dr. Williams agreed that there were grounds for optimism. “In the studies, ‘reproducible’ meant that individuals had similar findings when tested two weeks apart,“ he told us.
“That may not be true if tested 2 months apart or 2 years apart, [or] if there are changes in biological, psychological, or social conditions between tests. If changes occur under different conditions, that might mean that the person’s ‘fingerprint’ can change over time (or if circumstances change), as well,” added Dr. Williams.
“That provides reason for optimism, because that would mean their experience (the pain they feel) can be reduced, improved, or eliminated with the right combination of interventions. Chronic pain does not have to be ‘for ever’,” he noted.
Dr. Valentini plans further research: “Together with my collaborators, we feel that gamma and other brain oscillations are a crucial field of investigation for pain neuroscience. […] Perhaps, some of us will be able to replicate these analyses in chronic pain patients or patients with acute pain, thus addressing more directly the clinical relevance of our investigation.”
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