St. Louis

IN the 35 years since Peter Singer’s book “Animal Liberation” was published, jump-starting the animal rights movement in the United States, the number of animals used in cosmetics testing and scientific research has dropped significantly, and the number of dogs and cats killed in shelters has fallen by more than half. Nevertheless, because the amount of red meat that Americans eat per capita has held steady at more than 100 pounds a year as the population has increased, more animals than ever suffer from injuries and stress on factory farms.

Veal calves and gestating sows are so confined as to suffer painful bone and joint problems. The unnatural high-grain diets provided in feedlots cause severe gastric distress in many animals. And faulty or improperly used stun guns cause the painful deaths of thousands of cows and pigs a year.

We are most likely stuck with factory farms, given that they produce most of the beef and pork Americans consume. But it is still possible to reduce the animals’ discomfort  through neuroscience. Recent advances suggest it may soon be possible to genetically engineer livestock so that they suffer much less.

This prospect stems from a new understanding of how mammals sense pain. The brain, it turns out, has two separate pathways for perceiving pain: a sensory pathway that registers its location, quality (sharp, dull or burning, for example) and intensity, and a so-called affective pathway that senses the pain’s unpleasantness. This second pathway appears to be associated with activation of the brain’s anterior cingulate cortex, because people who have suffered damage to this part of the brain still feel pain but no longer find it unpleasant. (The same is true of people who are given morphine, because there are more receptors for opiates in the affective pain pathway than in the sensory pain pathway.)