Friday, February 19, 2010

Pain and suffering

This op-ed piece discusses how animals (presumably including humans) experience pain. It says that there are two components to pain: sensation and suffering. It is possible to turn off the suffering without turning off the sensation. (This is important so that an animal can feel a stimulus that it should avoid, such as a hot surface, even if the stimulus does not cause what we traditionally think of as pain.)

It then argues that since we can engineer animals so that they do not suffer when subjected to the conditions common factory farms, we should do it—not change the farms but change the animals so that they don't feel bad.

Seems like a very strange argument. Whether or not factory farms are ethical ways to treat animals, the argument seems to be saying that torture is ok as long as the victim doesn't suffer.

Along the way the claim is made that morphine works because it competes with the part of the brain that feels bad about pain, i.e., the part of the brain that suffers. When the suffering receptors are blocked by morphine, they are unable to respond to pain—hence no suffering.

The whole thing is an interesting description of how the brain works. I was unaware of it. Nor did I know we were so certain about this mechanism. It's strange to learn about it in such a strange op-ed piece, though.

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.)

Neuroscientists have found that by damaging a laboratory rat’s anterior cingulate cortex, or by injecting the rat with morphine, they can likewise block its affective perception of pain. The rat reacts to a heated cage floor by withdrawing its paws, but it doesn’t bother avoiding the places in its cage where it has learned the floor is likely to be heated up.

Recently, scientists have learned to genetically engineer animals so that they lack certain proteins that are important to the operation of the anterior cingulate cortex. Prof. Min Zhuo and his colleagues at the University of Toronto, for example, have bred mice lacking enzymes that operate in affective pain pathways. When these mice encounter a painful stimulus, they withdraw their paws normally, but they do not become hypersensitive to a subsequent painful stimulus, as ordinary mice do.

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