It Takes Two Hemispheres to Talk

Katja Heuer and Roberto Toro

Close your right eye. Now read this sentence out loud. If that was easy, you can thank the thick red band of braided neurons in the image above. The left eye sends what it sees to the right side of the brain, but reading and speaking take place largely on the left side, so the corpus callosum lets the two work together.

If the corpus callosum is severed — sometimes done to treat severe epilepsy — each side of the brain can act independently. For example, someone whose corpus callosum was severed might be aware of an animal jumping around the tree outside their window, but they would be unable to recognize it as a squirrel, because those functions rely on different sides of the brain. They can also perform multitasking feats like simultaneously copying a square with the right hand and a circle with the left.

About the Author

Charlie Wood

Charlie Wood is a science writer with a bachelor’s degree in physics from Brown University and a master’s degree in science journalism from New York University. In previous lives he taught physics in Mozambique and English in Japan, but these days he freelances from his home in New York.