How your brain could trick you into lying without knowing it, and other odd brain disorders

Author Sam Kean was sure that the scientists had got it wrong. He'd just read an account of a woman who suffered a brain injury that left her unable to speak. But somehow, she continued to sing. And when provoked, she'd swear. Yet another scientific paper discussed patients who woke up unable to recognise animals after they recovered from an attack of the herpes virus. A shoe? Yep. A maple tree? No problem. But the family's pet cat left them bewildered and at a loss.

"These papers were about brain damage that was so specific that I thought they could not possibly be true," says Kean, 36, of Washington. "I thought that the authors had made an error. I set out to prove them wrong, and I found that, of course, it was I who was wrong. I found these cases funny and kind of cool. I thought it would be interesting to find out how the brain works. That's when a light bulb went off in my head."

The result is the engaging and accessible history of the human brain, which travels back and forth between the 1500s to the present. Some case histories are extremely rare - a few gifted blind people can "see" through their tongues - while others provide insight into everyday questions, such as why some people struggle to remember faces. Kean spoke to about his new book .

It's like having someone else's hand attached to your body. The hand is yours, but on some level you're not controlling it. It's grabbing and doing things that you're not consciously willing it to do. It can be dangerous if it grabs the steering wheel or pulls a pot off the stove. Sometimes, it's more humorous. You might be pulling up your pants with one hand and pulling them down with the other.

What's going on is that the conscious part of most people's brains sends out a signal to one hand to do something, and to the other hand to inhibit it from doing that thing. If an apple is sitting in front of you, a healthy brain will send a signal to one hand to grab it. The other hand will get an inhibition signal saying, "OK, just cool it. The dominant hand is going to take care of this." If a passageway called the corpus callosum is broken or damaged or not working right, the other hand doesn't get the signal to stop, and reaches out and flails on its own.