What the Study Found
- A leg lift that set off a back pain flare made pain feel about 23% stronger and 26% more unpleasant, across 114 adults with chronic pain.
- During the flare, blood flow rose in two brain areas tied to thinking about yourself.
- A hot probe on the calf of the unmoved leg quieted one of those areas instead, the usual brain response to sharp pain.
- A faster heartbeat during the flare went with stronger pain, but only loosely, and breathing showed no link to pain.
IN a brain imaging study of adults with chronic lower back pain, a movement that provoked a flare of pain caused higher blood flow in two parts of the brain in the midline regions of the default mode network (DMN), a system linked to thinking about yourself that has typically been found to see less activity during episodes of sharp pain.
The test was simple: participants laid flat on a scanner bed while a researcher slowly lifted one of their legs until back pain climbed by two points on a 0 to 10 scale and then held it there for a full 10 seconds before repeating a second time. The test was designed to provoke a flare of pain on demand rather than waiting for one, a strategy earlier blood flow imaging of back pain had also used.
The team, led by Fadel Zeidan at the University of California San Diego, scanned 114 people aged between 21 and 65 who had lived with back pain for at least 3 months. Blood flow maps were usable for 99 of them. Across the two leg raises, pain intensity ratings rose about 23 percent on average, and unpleasantness rose about 26 percent. These ratings alone were fairly predictable, but what was not was how the DMN region lit up when normally this area becomes less active during sharp pain.
A Hot Probe Told a Different Story
The test established this expected pain response by pressing a hot probe (48 degrees Celsius, 118.4 Fahrenheit) to the calf of the subject’s unmoved leg in a heat pain test used as an exploratory reference. In response to the heat, frontal regions of the brain, including the medial prefrontal cortex – one of the key locations of the DMN – showed lower activity, which is the expected textbook pattern for sharp, salient pain.
The default mode network that lit up during back pain flares caused by lifting the leg is usually described as the brain’s idling mode, typically busiest when attention drifts inward to memory, worry and the self. Zeidan said the leg raise flipped the script on what has previously been understood about brain activity and pain.
“In every pain study, when you’re experiencing pain, the DMN deactivates,” said Zeidan, of the University of California San Diego School of Medicine. “What we show for the first time ever is that when you have a pain flare, it turns on instead. You start to identify the experience with who you are.”
The paper itself adds more caveats, calling the heat test a reference condition, not a control. Heat, it points out, was also scanned with a different signal from the blood flow maps, so the two conditions are not a clean like-for-like comparison. The idea of this being a first is narrower than it sounds as well: earlier work had already tied default mode regions to back pain getting worse.
Where the Back Lives in the Brain
After the leg raise, blood flow was higher in the medial prefrontal cortex and the posterior cingulate than when people lay supine. Both sit on the brain’s midline and belong to the default mode network. A resting scan of all 114 also linked the network’s connectivity to weekly pain severity, though that finding concerns everyday chronic pain, not the flare itself.
Heart rate did rise slightly along with pain intensity, but breathing remained unaffected.
What the Scans Cannot Say
Nobody without back pain took the test
and nobody did a painless movement for comparison, so the scans cannot separate pain from the leg lift or the posture itself. Positive leg raise responses were also a condition of joining, which means these results may not hold for people whose back pain does not respond that way, and the authors call for replication across pain subtypes. Interpreting the blood flow readings of default mode activity as self-focused thinking is also an inference, not something the scanner measures directly.
Then there is the question of treatment. Zeidan said mind-body and psychedelic approaches such as mindfulness and psilocybin target the whole person, not only the pain. The paper did not test any treatment, including psilocybin. Its own clinical suggestion is smaller: movement-evoked pain may need its own trials, because it engages systems unlike those behind pain at rest.
Reference
Gianola, M., Dean, J., Chen, C., Barrows, D., Riegner, G., Liu, T., & Zeidan, F. (2026). Brain mechanisms supporting movement-evoked chronic low back pain: an observational brain imaging study. British Journal of Anaesthesia. https://doi.org/10.1016/j.bja.2026.08.010
- Study type: Observational brain imaging study, a secondary analysis of the baseline visit of a randomised, placebo-controlled trial. Peer-reviewed, British Journal of Anaesthesia (In Press, Corrected Proof, online 5 October 2026).
- Sample size: 114 adults with chronic low back pain (aged 21–65, mean 45.9 years; 58 male, 56 female). Blood flow maps were analysed from 99.
- Exposure: Leg raise to a 2-point pain increase, held 10 seconds, performed twice during perfusion MRI (arterial spin labelling).
- Comparison group: The same participants lying supine. No group without back pain. Noxious heat (48°C) on the unaffected calf served as an exploratory reference.
- Follow-up: Single baseline visit, no follow-up.
- Funding / conflicts of interest: NIH National Center for Complementary and Integrative Health (R01AT009693) and the UC San Diego Sanford Institute for Empathy and Compassion. Authors declare no conflict of interest.
- Data availability: Not reported.
- Preregistration: Parent trial registered (NCT03354585). Registration of this secondary analysis not reported.
- Main limitation: Positive leg raise response was an inclusion criterion, so results may not generalise to leg-raise-negative patients (author-stated). Not author-stated: no pain-free or painless-movement comparison, so pain cannot be separated from movement.
FAQ
Does this mean mindfulness or psilocybin could ease back pain flares?
Mindfulness or psilocybin easing back pain flares is not something this study tested. The researchers tested no treatment, and psilocybin does not appear in the paper at all. Zeidan’s comments about whole-person approaches are his interpretation, and the paper’s own suggestion is narrower: movement-evoked pain may deserve its own place in trials of pain relief.
Why did the researchers lift a leg instead of waiting for a flare?
The researchers lifted a leg because a leg raise can provoke a flare on demand while a person lies in a scanner. The leg was raised until pain climbed by two points on a 0 to 10 scale and then held for 10 seconds. Waiting for a spontaneous flare would be unpredictable and hard to scan.
Can a faster heartbeat tell you how bad a back pain flare is?
A faster heartbeat tracked pain intensity during the leg raise, but only loosely. The correlation was r=0.26, and heart rate added about 7 percent in explained variance. A press release called it a reliable indicator, which is stronger than the numbers support.
Why can’t the scans prove that pain switched on the default mode network?
The scans cannot prove pain switched on the default mode network because no one without back pain took the test and no one did a painless movement. Blood flow changes could therefore reflect the leg lift or the posture as much as the pain. The study is observational, so it shows what travelled together, not what caused what.
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