Initially the outermost portion of that brain is what people test and see. There are deeper areas of the brain that are called subcortical areas. These are the areas that are designed for processing information and having different parts of the brain communicate with other parts. Sometimes injuries to these subcortical sections do not show up until more complicated or complex tasks are done. After an injury, one obviously does not perform strenuous tasks. Medical personnel, friends, and family help you with regular tasks. It is only after a person returns home and everyone feels that they are back to "normal" that a person is expected to resume their normal day-to-day living. A complicated task might be something as simple as balancing a checkbook or even tying shoes or remembering where your keys were.
Other complex tasks that require different parts of the brain to operate together at any point in time. These can be things such as balancing complicated hand activities involving dexterity, writing, engaging in conversations, and discussing what you did the other day. There are also more complicated tests that involve memory perception and analysis.