New research suggests that witnessing extreme pain – such as the injury or death of a comrade on the battlefield – has a lasting effect on how the brain processes potentially painful situations. The research team, chiefly from Bar-Ilan University and headed up by Moranne Eidelman-Rothman, investigated the brain using magnetoencephalography (MEG). Like more widely used fMRI (functional magnetic resonance imaging), MEG localises which parts of the brain are more active during a particular mental activity, but it offers more fine-grained information about when this activity is occurring. This sensitivity helped the researchers detect subtle anomalies in how pain is perceived.
Eidelman-Rothman’s participants were veterans of the Israeli Defence Force, 28 with battlefield experience, all of whom had been exposed to at least one event where a comrade was killed or seriously injured, and a control group of 16 veterans from noncombat units. The researchers scanned the participants’ brain activity while they viewed photographs of human hands and feet depicted in painful and non-painful situations, such as an axe directly striking the foot or striking a log a few inches away.
The results, published in Cognitive, Affective, & Behavioural Neuroscience, revealed an important difference in the neural activation patterns in the veterans and the noncombatants. Among the controls, brain activity specific to observing pain was seen within 220 miliseconds in right sensorimotor cortex and left posterior cingulate cortex (PCC) – these regions are part of what’s known as the brain’s “pain matrix”, which processes aversive stimuli – and later in a range of further areas, including the insula and right PCC, also part of the pain matrix. Crucially, among the battle veterans, this “pain effect” was absent from the PCC. It’s not that their response to the painful stimuli was subdued in the PCC compared with the control participants, but that their PCC response to the non-painful stimuli was enhanced, as if they were evaluating the potential for the situation to become suddenly painful – that the axe close to the foot was an injury waiting to happen. This was despite the fact that subjectively the two groups rated the photo types no differently, in terms of their unpleasantness.
Further work will be important to exclude the possibility that this neural hyper-vigilance to the potential for pain is purely driven by other factors, for instance, undiagnosed PTSD. But if it is the case that prior exposure to pain enduringly modifies our pain perception system, this has important implications for how we care for people – veterans, as well as survivors of accidents and natural disaster.