Colchester (UK): Every individual's experience of pain is unique but that makes it harder to treat. The experience of pain remains impenetrable to scientists because it is so variable. So researchers and clinicians still rely on subjective ratings, such as asking patients to rate their pain on a scale of zero to ten. But my recent work, in collaboration with my colleague Enrico Schulz and his team, showed new insights into a type of brainwave called gamma oscillations that scientists think may be linked to pain perception.
For the first time, we showed that gamma oscillations differ greatly between people, but that people's response pattern to pain stayed the same over time. In other words, people who show no waves when in pain will probably not show them in a subsequent recording (when experiencing pain again), whereas those who show a large response will probably show it again. Pain is variable by definition: the International Association for the Study of Pain defines it as a personal, unpleasant sensory and emotional experience that is influenced by biological, psychological and social factors.
Pain is often different in quality (dull, sharp, shocking, throbbing) and it may be hard to remember properly. To complicate matters, although nociception (the unconscious processing of unpleasant stimuli) usually leads to pain, research shows that one can exist without the other. An objective marker of pain would bypass the distortions caused by cognitive and social factors. And it would help patients who cannot communicate (such as those in a vegetative state) as well as young children and babies.
The long search for a pain gauge:Over the past few decades, technological advancements gave researchers the opportunity to finally start developing an objective measurement of pain. In the early 1990s, neuroimaging techniques such as PET scans and fMRIs became a popular way to study pain. This led to a focus on physiological measures of brain activity.
Scientists became excited by the idea of identifying some sort of pain centre or pain network within the brain. However, studies of the brain activation during pain experiments showed that even innocuous stimuli (for example, warmth, touch or vibration when participants weren't expecting it) can activate the brain similarly to painful stimuli.
Studies have also shown that the brain's response to painful heat is strongly influenced by the person's level of alertness and attention. Both your brain response and your conscious perception of pain are influenced by how much attention you pay to it. There is growing evidence that brain response to pain doesn't always have a meaningful relationship to the level of pain a person is experiencing heightened brain activity doesn't always mean heightened pain.
Contextual factors, study methodology and biological differences between people can all affect brain activity. So, it became clear that technology alone wouldn't give us an objective measure of pain. Researchers needed to understand more about the brain's response to stimulation.