SANDI THURBER, GRAYSON, GEORGIA: My name is Sandi Thurber. And I'm from Grayson, Georgia. And I'd like to ask CNN a question: Why does the left side of the brain control the right side of the body?</s>DR. SANJAY GUPTA, CNN MEDICAL CORRESPONDENT: Nobody knows why the left side of the brain controls the right side of the body. But being a neurosurgeon, this is a particular interest of mine. And this is how it happens: There are several fibers or tracks that originate in the brain. They're responsible for your movement and your pain and temperature sensations. They pass down from various centers in the brain and end up in the spinal cord. But here's the neat thing: Most of them actually cross before getting there. Some cross right at the top of the spinal cord and some much lower down. The end result: When you lift your right hand, that signal came from the left side of your brain.
Ask CNN: Why Does the Left Side of the Brain Control the Right Side of the Body?