See Carl Zimmer's new ebook, Brain Cuttings, available at Amazon, Barnes and Noble, and carlzimmer.com.
This month’s column is a tale of two rats. One rat got lots of attention from its mother when it was young; she licked its fur many times a day. The other rat had a different experience. Its mother hardly licked its fur at all. The two rats grew up and turned out to be very different. The neglected rat was easily startled by noises. It was reluctant to explore new places. When it experienced stress, it churned out lots of hormones. Meanwhile, the rat that had gotten more attention from its mother was not so easily startled, was more curious, and did not suffer surges of stress hormones.
The same basic tale has repeated itself hundreds of times in a number of labs. The experiences rats had when they were young altered their behavior as adults. We all intuit that this holds true for people, too, if you replace fur-licking with school, television, family troubles, and all the other experiences that children have. But there’s a major puzzle lurking underneath this seemingly obvious fact of life. Our brains develop according to a recipe encoded in our genes. Each of our brain cells contains the same set of genes we were born with and uses those genes to build proteins and other molecules throughout its life. The sequence of DNA in those genes is pretty much fixed. For experiences to produce long-term changes in how we behave, they must be somehow able to reach into our brains and alter how those genes work.
