What Is A Quantitative EEG?
Quantitative electroencephalography (QEEG) began in the 1970's as a way of using computers to extract more information from raw brain wave data than was possible by the traditional approach of looking at brain wave tracings on paper. Although many abnormal patterns of brain wave activity are readily apparent during visual inspection, such as the "spike and wave" associated with epileptic seizures, others can be seen by a computer in ways not possible with the human eye. Your digitized brain wave data can be compared to a normative database to determine if your EEG contains activity that is significantly different from what is normal for someone of your age. That information is then used to formulate an individualized neurofeedback treatment plan to help you return your brain to a normal and efficient mode of functioning.
What Does A QEEG Tell You About
Your Brain?
A QEEG will give you information
on a number of aspects of your brain wave functioning:
| 1) Relative power is an indication of the amount of activity in one of the major brain waves bands (beta, alpha, theta, and delta) as compared to activity in the other bands. Activity in each band is compared to the other bands at 16 locations in the brain. It is common to find excesses in relative power that are indicative of problems. For example, increased relative alpha power in the front of the brain is often seen in persons with attention problems. Alpha is typically strongest in the back of the brain. |
| 2) Coherence is a measure of how much activity is shared between different parts of your brain. High coherence between two locations means that they are working too closely together. Low coherence means that they are not working together enough. Both indicate that the brain is working inefficiently. High coherence is often seen in persons who have suffered a traumatic brain injury. |
| 3) Phase is a measure of the speed with which signals travel through your brain. Negative phase reflects an increase in speed, while positive phase means that signals are traveling too slowly. Both impair a person's ability to efficiently process information. The speed of information moving through your brain can be compared to trying to hit a baseball. A ball that comes at you at medium speed is easy to hit. If the pitcher throws a fastball, the ball may have passed you before your bat can touch it. A slow, high pitch can also be hard to hit. |
| 4) Eyes closed versus eyes open activity. Your brain works differently when your eyes are open as compared to when they are closed. For example, alpha activity in the back of your brain should go down significantly when you open your eyes. In general, the speed at which the brain operates should increase when the eyes are open. QEEG's in persons with ADD/ADHD often show that their brains do not speed up or actually slow down when they open their eyes and concentrate on a task such as reading. |
Digitized EEG data can also be used to perform a discriminant analysis, which is the use of a mathematical formula to separate people into diagnostic groups based on specific characteristics of their EEG. A frequently used QEEG discriminant function has been shown to be 90 percent accurate in distinguishing between persons with a common form of ADHD and those who don't have it. Discriminant analysis, in conjunction with other information about a patient, is used to assist in diagnosis of ADD/ADHD, traumatic brain injury, depression, and other disorders.
How Is A QEEG Performed?
A QEEG is performed while you are
awake and sitting in a comfortable chair. The first 30 to 45 minutes of
the QEEG session is devoted to placement of the EEG sensors on your head.
Until relatively recently, each of the 19 scalp electrodes had to be individually
glued on. However, the development of an electrode cap has made the process
much easier. The cap, which looks like a mesh fabric shower cap, has the
electrodes implanted in it. It is placed on your head and conductive paste
is squirted into the electrodes to assure that they make a good connection
with your scalp. Two other electrodes, which look like clip-on earrings,
are attached to your ears. Most people find that the cap and ear clip electrodes
cause very little discomfort.
Once the cap and ear electrodes are in place and their connections have been checked, ten minutes of eyes closed and eyes open brain wave activity is recorded. You will be asked to sit with your eyes closed and remain as still as possible and then sit with your eyes fixed on a particular spot to help reduce eye movement. The brain functions differently with the eyes open versus eyes closed, so seeing how your brain is working in both conditions is important. In some instances another ten minutes of brain wave activity is recorded during performance of a task, such as reading or doing mathematics.
If you or your child have a hard time sitting still for long periods of time, that will not be a problem. The QEEG unit collects data in 315 two-second periods. Analysis of the data can be performed with as little as 25 movement-free periods and they don't have to be consecutive.