I have no clue. You'd have to find a chinchilla psychologist!
I have heard that squirrels can have Downs syndrome and act retarded though. In those cases there are usually physical abnormalities as well and can only survive in captivity because they have no sense of fear. I remember having a few farm animals with issues in the past. There was a dog I had that was really stupid and got killed by a horse. Its offspring were stupid too. It had a puppy that had to be an indoor pet. One day they (our friends who adopted it) took it out hiking in the desert and he ate a cactus bigger than his mouth and it had to extricated by a veterinarian. Oddly enough that dog lived long enough to die of natural causes. I remember a couple of chickens and ducks that were like that too but they weren't as fortunate because they had to live outside. It's not very common but it does happen.
