How exactly do you think scientists investigate which areas of animal (and human) brains are responsible for which functional area ? With humans it comes from

How exactly do you think scientists investigate which areas of animal (and human) brains are responsible for which functional area ? With humans it comes from papers describing the treatment of "brain trauma". Within animals, where the majority of research is done, depending on the animal, they just nail them to a board, or nail a board or a wire into their skull, cut out half the brain, insert some sensors, and record data in the few hours that the pain does not totally immobilise the animals, usually while making the animal perform some trick, like navigating a maze, or looking at prey, or ...