Chronic lower back pain: study reveals why treatments do not always work – the brain ‘misinterprets’ pain

The WHO makes this very clear. Low back pain, pain localised in the lower back, is the leading cause of disability worldwide and is often ‘triggered’ by movement. When the pain persists for more than 12 weeks, it becomes chronic, with the pain itself effectively escaping the body’s control and becoming a separate condition in its own right. These are undoubtedly the most complex cases to tackle, not least because traditional treatments do not always prove successful. In such cases, perhaps, we need to study the brain in detail, particularly if the pain flares up in response to movement. And to focus on its ‘sense of identity’: over time, episodes of pain could in fact mistakenly trigger reactions in specific populations of neurons, leading to unexpected responses that render traditionally used drugs ineffective. A study conducted by experts at the University of California, San Diego, published in the *British Journal of Anaesthesia*, links neurology and personality in the response to chronic pain. It suggests that persistent back pain may be deeply intertwined with a person’s sense of identity, potentially helping to explain why conventional pain treatments often offer only limited relief.

Experts have identified an unexpected response from a particular neural circuit, involving the brain’s default mode network (DMN), also known as the ‘self-network’. This structure is made up of interconnected regions in the frontal, parietal and temporal lobes. These areas are particularly active when our attention turns inwards, for example when we reflect on personal experiences, think about our identity or consider our thoughts and emotions. Conversely, the network generally becomes less active when we direct our attention towards something happening around us. According to the study, sudden back pain triggers a response that is diametrically opposed to what might be expected. In practice, rather than deactivating the network, it stimulates it, with a reaction that goes far beyond physical sensations, to the extent that it suggests that, in some cases, brain systems involved in people’s perception of themselves may be involved. “It is now well-established knowledge amongst us researchers in the field, thanks above all to the studies of Vania Apkarian, that chronic pain, whatever its cause, is associated with the activation of specific networks (i.e. neural connections in the brain), which ‘enrich and complement’ physical pain with psycho-emotional content,” comments Arturo Cuomo, former Head of the Department of Anaesthesia, Resuscitation and Pain Management at the IRCCS Pascale in Naples and President of the Partenos Association. Among these networks, particular attention is paid to the Default Mode Network (DMN), which under normal conditions is activated only during introspective thought but, in patients with persistent pain, is continuously activated, causing their brains to focus solely on pain through obsessive and continuous rumination, which, over time, leads to functional disability with a strong psychosocial component”.

The study examined 114 patients with chronic lower back pain who underwent the ‘straight leg raise test’, which can trigger lower back pain. During the examination, changes in blood flow in the brain were assessed using a special type of functional magnetic resonance imaging (fMRI), alongside the participants’ response to another stimulus, such as a burning sensation in the calf.

When movement triggered a flare-up of chronic back pain, the DMN (default mode network) became more active, whereas this did not occur following a thermal stimulus. Not only that: patients with more severe chronic back pain showed stronger connections between the DMN and the primary somatosensory cortex, the brain region responsible for processing physical sensations, including signals from the back, and when pain intensity was higher during the leg-raising test, greater activity was observed in the brain regions involved in sensation and movement, accompanied by an increase in heart rate. In short: it appears that flare-ups of chronic pain involve brain processes associated with personal identity, not just the physical experience of pain. Movement-related chronic back pain, therefore, produces the opposite effect to acute pain. “In every study on pain, when pain is felt, the DMN deactivates” – this is the comment by the corresponding author Fadel Zeidan in a note from the Californian university. “We are demonstrating for the very first time that, when pain flares up, the DMN becomes active. One begins to identify the experience with one’s own identity.”

In short, the study reveals that pain somehow ‘takes hold’ of the brain to such an extent that it becomes linked to personal memories, expectations and emotional experiences. All of this leads to an extension (in duration and intensity) of the pain sensation, linked to memories of previous episodes and the fear of a relapse. Above all, the research paves the way for treatments that do not merely aim to suppress pain stimuli – given that these may not work perfectly in cases of lower back pain – but rather seek to intervene on the DMN. For example, in some patients it may be necessary to go beyond the use of drugs such as opioids, which act primarily on pain signalling but may not adequately target the brain networks involved in the emotional and personal dimensions of persistent pain.