Idiom: to study one’s brains out

Context #1:

Jim:  How did you do on the grammar test?
Sam: I got 100%.  I studied my brains out for that test.
Jim:  Nice job!

Context #2:

Chrissy: Are you preparing for the GRE exam?
Tammy: Yeah, I’ve been studying my brains out for the last 6 months.
Chrissy:  Well I’m sure you’ll do great!

Meaning: to study one’s brains out means to study extremely hard for something.