Illustration of cerebrum
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The cerebrum is the largest part of your brain. It's what you probably visualize when you think of brains in general. The outermost layer of the cerebrum is the cerebral cortex, the "gray matter" of the brain. Deep folds and wrinkles in the brain increase the surface area of the gray matter, so more information can be processed.

The cerebrum is divided into two halves (hemispheres) by a deep fissure. The hemispheres communicate with each other through a thick tract of nerves, called the corpus callosum, at the base of the fissure. In fact, messages to and from one side of the body are usually handled by the opposite side of the brain.