No man can use his brain to think for another.
If so, four and a half years ago he had not used his brain much.
But if he used his brain, that would be enough.
He'd have to start using his brain again, at least.
It was the first time I had used my brain.
So she had to use her brain, such as it was.
"Now I am beginning to learn to use my brain."
When people have stopped to use their brain, there's not much you can do.
They make you use your brain to come up with different strategies.
"If you want to live through this, you'd better start using your brain."