neurological testing

There was a good discussion on testing of Wernicke’s area and how to go about validating the damage.

http://theness.com/neurologicablog/?p=3164
But it is impossible to completely isolate one subsystem within the brain, and so other functions can interfere with our testing, and we have to tease this out by using multiple tasks and then triangulating to the common element that seems to be causing trouble. This is most true for cognitive function.

For example, if I want to test Wernicke’s area (in the superior posterior temporal lobe) I will give the patient several verbal commands (without non-verbal cues) and see if they can interpret them. Wernicke’s area translates ideas into words and words into ideas, and so we test its function by testing verbal comprehension. However, in order to test this one piece of the brain, the patient also needs to be able to attend to the exam (they need to be alert and attentive), then need to be able to hear and get that information to Wernicke’s area, they need to have the general cognitive ability to understand what is happening and that they are expected to do something, and they need to be able to move to execute whatever command I gave them. And they may decide just to be uncooperative with the exam, for whatever reason. So many parts of the brain and nervous system need to work together to perform even a simple task.
We isolate Wernicke’s function, and other functions, by controlling for variables. So I will give the patient many commands, some easier for Wernicke’s area to interpret, and others more challenging – but with all other variables being equal. If commands that are difficult from a language comprehension point of view are what give the patient the most difficulty, then that is probably the part of the brain that is not working.

Wernicke’s area is mapped on lots of brain maps so the neurologist should be able to tell from the beginning on the 3d MRI if that area was directly affected. And use that same MRI to see how much of the white area underlying it was damaged or dead. By starting from this point the trial and error method could become a lot more scientific. Please any neurologists reading this, educate us survivors on why this wouldn't work.