Pain produces memory gain

Pain can sear memories into the brain, a new study finds. A full year after viewing a picture of a random, neutral object, people could remember it better if they had been feeling painful heat when they first saw it.

“The results are fun, they are interesting and they are provocative,” says neuroscientist A. Vania Apkarian of Northwestern University in Chicago. The findings “speak to the idea that pain really engages memory.”

Neuroscientists G. Elliott Wimmer and Christian Büchel of University Medical Center Hamburg-Eppendorf in Germany reported the results in a paper online at BioRxiv.org first posted December 24 and revised January 6. The findings are under review at a journal, and Wimmer declined to comment on the study until it is accepted for publication. 

Wimmer and Büchel recruited 31 brave souls who agreed to feel pain delivered by a heat-delivering thermode on their left forearms. Each person’s pain sensitivity was used to calibrate the amount of heat they received in the experiment, which was either not painful (a 2 on an 8-point scale) or the highest a person could endure multiple times (a full 8). While undergoing a functional MRI scan, participants looked at a series of pictures of unremarkable household objects, such as a camera, sometimes feeling pain and sometimes not.

Right after seeing the images, the people took a pop quiz in which they answered whether an object was familiar. Pain didn’t influence memory right away. Right after their ordeal, participants remembered about three-quarters of the previously seen objects, regardless of whether pain was present, the researchers found.

But a year later, pain reigned supreme. People had a better memory for objects viewed while experiencing an 8 on the pain scale than objects viewed while feeling a 2.

The results suggest that pain “somehow amplifies or stamps in the memories so that they are stored more robustly,” says neuroscientist Ben Seymour of the University of Cambridge in England. By showing that pain can preserve memories for at least a year, the study highlights the power of pain to sculpt behavior, he says. And the experiment probably doesn’t capture the full extent of many painful experiences. As gruesome as 8-out-of-8 heat pain sounds, that’s probably nowhere near what someone might feel during a medical procedure or a nasty accident, Seymour says.

Based on fMRI brain scans, pain’s memory boost appeared linked to activity in a part of the insula, a brain area involved in bodily sensations and emotions. Other studies have found that emotionally charged memories seem to be particularly durable.

Apkarian cautions that other parts of the brain, particularly those in the medial temporal lobe that have known roles in memory, are likely to be involved.

Finding that pain can provide a memory jolt agrees with a mountain of animal data, Apkarian points out. Scientists know that one of the quickest ways to make a mouse learn something is to shock it. But “the human component of that is badly missing,” he says. “I would consider this a first step,” he says.