How do they know what chemicals your brain is producing in response to certain stimuli when it should involve opening your head to watch it?

Question

They say that the brain releases dopamine when X happens, or releases oxytocin when X happens, etc. How do we know that’s happening inside somebody’s head without cracking their skull open?

In: Biology

Answer 1

well with rats, you do that. You gave them stimuli, then decapitate and measure contents.
(or do it live)

then we use that data and assume it happens similiar in other brains