Chronic back pain may activate an unexpected brain network, study finds

For people with chronic back pain, everyday movements like bending down to tie their shoes or picking up a grocery bag can trigger painful flare-ups.

Now, scientists have made a surprising discovery: These episodes may activate a brain network that's associated with our sense of self.

In a new study, the researchers found that movement-induced chronic back pain was tied to increased activity in the brain's default mode network , a group of connected brain regions that lights up during self-reflection and mind wandering.

This finding was unexpected because the network typically becomes less active during acute pain, such as transient pain triggered from touching a hot stove or banging your knee on a table.

The new study, published Oct.

5 in the British Journal of Anaesthesia , suggests that chronic-pain flare-ups may involve brain processes beyond those responsible for detecting painful sensations.

How the brain responds to chronic pain Chronic lower back pain , defined as lasting at least three months, is a leading cause of disability worldwide.

It's thought that when chronic pain first begins, a network of regions in the brain called the " pain neuromatrix " becomes sensitized so that the pain persists even after the painful stimulus is gone.

Although scientists know that chronic pain is associated with changes in brain activity , they don't fully understand what happens when movements trigger sudden increases in that ongoing pain.

To investigate, researchers recruited 114 adults with chronic lower back pain and used functional magnetic resonance imaging (fMRI) to examine their brain activity. fMRI measures changes in blood flow, which acts as an indirect measure of brain activity.

After an initial scan, a researcher helped lift each participant's leg until their back pain increased, held it in position for 10 seconds, and then lowered it.

The researchers scanned the participants' brains immediately after this pain-inducing leg movement and compared the results with scans collected beforehand.

On average, the test increased the participants' reported pain intensity by 23%.

As expected, during the leg movement, the researchers observed increased blood flow in brain regions involved in processing pain and movement.