From an interview with Minksy:

Pleasure, like pain, is thought of as being a sort of simple, absolute, innate, basic thing, but as far as I can see, pleasure is a piece of machinery for turning off various parts of the brain. It’s like sleep. I suspect that pleasure is mainly used to turn off parts of the brain so you can keep fresh the memories of things you’re trying to learn. It protects the short-term memory buffers. That’s one theory of pleasure. However, it has a bug, which is, if you gain control of it, you’ll keep doing it: If you can control your pleasure center, then you can turn off your brain. That’s a very serious bug, and it causes addiction. That’s what I think the football fans are doing—and the pop music fans and the television watchers, and so forth. They’re suppressing their regular goals and doing something else. It can be a very serious bug, as we’re starting to see in the young people who play computer games until they get fat.