Doctors can measure activity in her brain.
The accident left him with permanent brain damage.
His wife died from a brain tumour.
He said the Martians opened his head and [did] experi[ments] with his brain. (Preliminary English Test; B1; Spanish)
That can't possibly be the right way to do it - use your brain!
He's got brains but he's too lazy to use them.
The whole [of] Western society already seems to be founded on computers and relying on chips, which to a certain extent has taken away our own abilities of using our brains. (Certificate in Advanced English; C1; Dutch)