One of the first assessments of brain function and brain disorders involve the physiological and behavioral changes in a person. Since the brain controls a lot of our responses, we can assume that certain abnormal responses might be the result of different kinds of brain damage or problems with the brain function.
Now, these can be very obvious and profound differences. For instance, stroke patients might have noticeable difficulty moving or speaking, though they can also have more subtle signs.
A neurological soft sign is a term used for minor signs of nonspecific sorts of brain disorders. These are symptoms that might not normally be noticed by others, but psychologists are more trained to recognize and understand them as signs of neurological problems.
Besides noticing the outward behaviors that people might show as results of neurological problems, the brain structure itself can be analyzed. There are specific tools that scientists and psychologists use to measure the brain and its function. These tools either map or model the brain, generally in 3D.
Essentially, the computed tomography (CT) scan is a specialized x-ray device. It takes x-rays of the brain, taking multiple images, and then creates a 3D model of the brain from those multiple images. They can show some of the internal structures just like x-rays normally do.
Here is a CT scan of the brain:
A magnetic resonance imaging (MRI) device uses magnetic fields to provide more internal images of the structures of the brain in 3D. It doesn't use any radiation, like an x-ray device or CT scan. In that way, it's a bit safer for the person who's using it.
This is a tool that measures the brain's function itself, meaning that it doesn't just take a map or a picture, but rather shows how the brain is active over time through different sorts of behaviors. It is used to show which areas of the brain are related to certain kinds of thoughts and actions. In this way, it's a bit more comprehensive than some of the other brain structure tools.
Here is an MRI of the side view of the head. You can see the nose, lips, eye socket, brain, and lips.
On the other hand, a functional MRI (fMRI) will show blood flow to areas over a lapsed period of time.
EXAMPLEIf you wanted to see which areas of the brain were active when a person is dreaming, you would use a functioning tool, or fMRI.
An EEG or electroencephalograph is a device that places electrodes on a person's brain--therefore not very invasive--to amplify and measure all of the brain's different electrical activity in certain areas of the brain.
It can show the brain waves of specific areas of the brain, but they're very simple, and they don't actually show much of a concrete image--generally, just little lines on a piece of paper.
To actually get a picture, a positron emission tomography (PET) scan would be used. The PET scan resembles a tunnel. An individual is injected with a radioactive fluid, called a tracer. Once the tracer has been injected into the blood, the individual conducts behavior or thinks about certain kinds of things. The radioactive tracer travels to those specific areas that are active.
The PET scan shows the areas where the blood flow is most prominent; they light up in the PET scan, indicating that those are the areas being used for that certain type of behavior.
The image below shows a PET scan of a human brain with Alzheimer's disease.