: always in one's thoughts I've had pizza on the brain all day. He's got sex on the brain.

What is the idiom on the brain in a sentence?

to not be able to stop thinking or talking about one particular thing: You've got cars on the brain.

What is the brain simple definition?

1 : the part of the nervous system that is inside the skull, consists of grayish nerve cells and whitish nerve fibers, and is the organ of thought and the central control point for the nervous system. 2 : the ability to think : intelligence. 3 : someone who is very smart.