Electroencephalography (EEG) is the measurement of electrical patterns at the surface of the scalp, which reflect cortical activity, and are commonly referred to as “brainwaves”.
Quantitative EEG (QEEG) is the analysis of the digitized EEG, and is sometimes referred to as “Brain Mapping”. The QEEG is an extension of the analysis of the visual EEG interpretation that may assist and even augment our understanding of the EEG and brain function.
Starting in the 1970s it became possible to store the EEG signals on computer media for later analysis. As computers and electronic amplifiers became smaller and faster, and as mathematical methods developed, it has become possible to store 19 or more channels of EEG data on a laptop computer using an amplifier the size of a hardback book. Often the sensors are attached to the inner surface of a cloth or mesh cap. The caps come in various sizes so that the sensors will be accurately placed on any size head.
The computer is capable of recognizing many more and subtle patterns among the brain waves in various locations than the eye can normally see. These patterns are then graphically displayed as colored brain maps, tables, and charts. Despite the impressive ability to detect subtle significant patterns, the raw EEG must always be analyzed by a trained eye in order to avoid misinterpretation or ambiguity in the QEEG.
A very special feature of modern QEEG is that all the data from a client's recording can be compared to several databases of 'normal' individual’s brainwaves. This makes it much easier to spot statistically significant deviations. These deviations may or not be clinically significant. It is important to consider them in light of any complaints or conditions the client might have in order to better appreciate their significance if any.
Much of the groundbreaking work in neurofeedback was done without the aid of QEEG. Many practitioners still use protocols that are generally but not always safe and provide the ability for most brains to develop flexibility and increased control. Studies (references to come) have suggested that for some populations QEEG-driven neurofeedback is more effective. The differences between what are commonly called EEG and QEEG is that EEG reading always involves deep attention to the raw EEG and perhaps a few quantified metrics such as peak frequency.
This is the form most commonly used in hospitals and neurology practices. Neurofeedback and research have a particular interest in maps and charts that are completely made from mathematical measurements on the raw EEG. These so-called QEEG brain maps are often used in developing strategies for neuromodulation.
The client's head is measured to determine which size sensor cap will be used. The caps are comfortable and it is easy and quick to prepare them to record a high-quality signal. The cap is plugged into a 32 channel Mitsar amplifier which is controlled by the WinEEG software www.novatecheeg.com. The sensors in the cap are optically isolated from the power to avoid any risk of shock. Once the EEG is obtained it can be analyzed further with the WinEEG software and the Human Brain Index database www.mitsar-medical.com or exported to be analyzed with the Neuroguide database www.appliedneuroscience.com or the Sterman-Kaiser SKIL database www.skiltopo.com.
The cap and its sensors must be positioned according to the International 10-20 system; the sensors must be prepped with special conductive gel and the connection of each sensor with the scalp must be tested; the client must be comfortable and watched for any unnecessary movements of body or hardware. Sometime after capturing the EEG recording, it must be carefully examined by eye in order to judge its quality and any gross indicators of problems.
If the goal is to compare complex measurements of the client’s EEG with those of a database of expected values, then it will be necessary to carefully isolate just those sections of the recording that are free of “artifacts”. An artifact refers to a signal embedded in the scalp recording that comes from movement or the environment or is otherwise not related to brain electrical produced by a non-drowsy brain in a resting state. Usually, such recordings include one or more taken with