Injured Squids Teach the Purpose of Pain

The behavior of injured squids provides real-time insight into why intense pain can often persist long after an injury has been inflicted, a new study suggests.

The study, recently published in the peer-reviewed journal Current Biology,  details how squids that experience the pain of an injury are far more likely to become extra vigilant for sources of harm, directly resulting in a higher chance of survival day-by-day.

Researchers working out of the Marine Biological Laboratory at Woods Hole, Mass., were able to determine this after studying the behavior of injured squids (Doryteuthis pealeii) in a tank with their natural predator, the black sea bass.

According to the study, researchers found that a minor injury to one of a squid's arms did not do much to inhibit free movement around the tank. However, the injury still promoted the sea bass to target the injured squid more often than uninjured squid. In this type of environment, it was naturally beneficial for injured squids to be more alert of their surroundings, and to travel around the tank in a highly defensive manner.

To show that persistent pain after an injury was directly associated with this increased alertness, the researchers briefly treated some injured squids with a light anesthetic that prevented them from feeling their injuries . The researchers observed that squids who could not feel their pain continued to act like the uninjured squids in the tank and tended to survive significantly shorter periods of time, compared to squids left to feel their injury's persistent pain.

So what does this teach us? While the persistent pain of something like a paper-cut seems like nothing more than a nuisance to modern-day humans, it may have been a vital defensive trait that kept our evolutionary ancestors alive.

According to first author of the study, Robyn Cook, understanding pain sensitivity in an evolutionary context is an important step towards other applications of pain study.

"If we can understand more about what the natural, 'intended' purpose of nociceptive sensitization is, we might be in a better position to find new ways to treat its pathological expression in humans," Crook said in an accompanying press release.

The study was published in Current Biology, a Cell publication, on May 8.