BEIJING, May 9 (Xinhuanet) -- For many of us, the unpleasantness of being in pain often goes beyond the agony of the injury. If we are in excruciating discomfort, suddenly it seems everything bothers us -- sounds are too loud, lights are too bright, and even a gentle touch can be uncomfortable.
A new study involving injured squid and hungry sea bass may help explain why we are so grumpy and irritable when we are in pain, according to media reports.
"One of the effects of pain is the peripheral sensory system becomes hyperactive," said Edgar T. Walters, who studies pain and neural plasticity at the University of Texas Medical School at Houston. "People in pain are very easily irritated and we found that this fits in with a primitive pattern designed for an animal to be extra-vigilant."
The researchers put four injured squid in a tank with four squid predators -- in this case, sea bass. Then they compared the injured squids' behavior to four non-injured squid who were put in the same predator-heavy conditions.
The injury was subtle enough that it didn't affect the squid's ability to swim or maneuver in the water. However, the researchers found it did affect the behavior of the squid.
The researchers also noticed that the sea bass were much more likely to hunt the injured squid. Even though the researchers could not discern any difference in the swimming ability of the injured and non-injured squid, the sea bass clearly could.
"Obviously the fish are evolved to detect the most vulnerable prey, which goes to show just how costly a really minor injury can be to an animal," Crook said.
In another experiment, the researchers anesthetized the squid before snipping its arm. These squid were not hyper vigilant, but they were still more attractive to the sea bass, and therefore, they were more likely to be eaten than the injured squid who had not been anesthetized and were super sensitive to any perceived threat.
It seemed the hyper vigilance of the injured squid served a useful purpose, leading the researchers to conclude that there is an evolutionary benefit to that hypersensitive sensory state we often find ourselves in after an injury.