There's a simple cognitive test that humans tend to fail— at least, they fail when their performance is compared to the performance of rats. Why? Because our brains screw us up. But a specific brain injury can bring us up to rat-level.
First let's imagine a simple game, with potentially great rewards. You will see a series of cards put up in front of you. Each successive card will be either red or green. You will try to guess which color it is beforehand. If you guess correctly, you get a little reward. Obviously, at first, your guesses will be completely random, but observing the sequence of cards should help you figure out a strategy to use.
I'll spare you the actual sequence of the game, but the best strategy is pretty simple — always pick green. The cards are randomly drawn from a deck that is 75% green. Most people don't understand this. They keep assuming that there is a pattern to the drawn cards, and if they can only find it, they will be able to reap the rewards on every card. They try to match their red guesses to when a red card "should" show up, never quite getting that "should" isn't part of the game. Rats, on the other hand, do as well as it is possible to do on the game. They are willing to work for nothing 25% of the time for a 75% gain. Or perhaps they're not tortured by the idea that there is a pattern that they're somehow not guessing. When it comes to this test, humans are either straight-up foolish, or so smart that we make ourselves dumb.
There's one group of people who perform as well as rats, but they only do it about half the time; they're known as split-brain patients. Either through injury or surgical intervention, the connections between the two halves of their brain are severed, so the two halves of the brain can't communicate. If something happens to the side of their body that the right half of the brain controls, but the left half of the brain has to deal with it (for example, only the hand controlled by the left hand of the brain is free), they literally can't cope. For example, the right hand can't write down or draw the image the left side of the body is seeing.
These people are the subject of frequent experiments, and in time, researchers got around to trying out this experiment, too. It appears the our problems with the test come from letting that pesky left hemisphere of the brain take over the good sense we hear from the right hemisphere. When the people "decided" with only the left hemisphere of their brain, they tried to guess the pattern of red and green every time. When they used only the right hemisphere of their brain, they went with the more-frequent color and reaped the higher rewards. Our right brain is as smart as a rat! The left brain? Not so much.
[Via The Drunkard's Walk]