Brain
To dream of a brain represents intellectual capability or the ability to think. It reflects problem solving, brainstorming, creativity, and insight.
To dream of the brain being eaten, attacked, or taken over represents factors in your life that have a powerful effect on your thinking.
To dream of brain surgery represents a significant change to the way you think. A person or situation that's motivating you to eliminate a longstanding block to your creativity, communication, or success.
The brain differs from the whole head as a symbol in that the head is more about personality, attitude, and perspective. The brain is more about processing and figuring things out.
Example: A woman dreamed of her brain being used by other people to do drugs and never being able to get it back. In waking life she was recovering from meth addiction while her boyfriend was still an addict.