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OVERVIEW AND HISTORICAL

DEVELOPMENT OF QEEG

Definition:Quantitative EEG, also known as neurometrics or brainmapping, is a method of measuring and analyzing brain electrical activity that can be used to estimate the probability that the quantitative features reflect dysfunction or deviation from normal (Senf, 1988).

Historical Background: Interest in gaining clinically useful information from brain electrical activity began shortly after Berger’s discovery of the Alpha rhythm about 75 years ago.QEEG is an extension of electroencephalography; but unlike traditional EEG which is done only by visual inspection of the record, qEEG allows EEG records to be quantitatively analyzed.The new analysis was made possible by advances in electronics, microcomputers, and mathematics. Years of standard visual EEG analysis of brainwave activity by neurologists and electroencephalographers failed to yield reliably valid information about clinical phenomena that were obviously related to brain function, such as depression, brain injury, and learning disabilities. Mathematical analysis of brain electrical activity was pioneered in the 1950’s by Grey Walter.Instrumentation to measure the electrical energy contained in various frequency bands was developed in the late 1960’s by Matousek.

Description:QEEG provides a methodology for the measurement of electrical energy contained in various frequency or Hertz bands (delta, theta, alpha, beta).It uses sampling methods to perform analogue to digital conversion of raw EEG signals that in turn enable computerized mathematical analysis of various characteristics of the EEG activity.Gradations of electrical activity across bands can be displayed by color coded topographical displays of variations in the electrical activity under different conditions and organism states.

Digitized EEG data can be subjected to mathematical manipulations to produce several variables descriptive of the overall, or average, EEG activity, in a person’s record.These variables can be used to compare an individual’s EEG record to those of persons of similar age to determine how the individual’s activity differs from normality.

Standard variables generated through QEEG mathematical calculations of digitized EEG data include:

1.absolute power – the electrical energy measured at each electrode site, measuredin microvolts squared

2.relative power –the distribution of the power within each frequency band at each site

3.power asymmetry – the symmetry of power between right and left hemispheres at each electrode site

4.coherence – the coordination of the electrical signal, irrespective of its power, between homologous sites in the left and right hemispheres

QEEG Normative Databases:The clinical validity and dependability ofa reference comparison system such as qEEG is dependent upon the quality of the various databases being used.The rules of the mathematics applied in such analytical systems must be carefully adhered to, i.e. respect for the strictures of the normal curve and probability theory.

Research and development of normal and diagnostic discriminant function EEG databases began with federal funding assistance in the 1970’s (E. Roy John, Neurometrics/NXLink) and 1980’s (Frank Duffy, BEAM).Robert Thatcher’s NeuroGuide in the 1980’s and William Hudspeth’s NeuroRep program in the 1990’s built on the work of John and Duffy.In the late 1990’s, Barry Sterman’s and David Kaiser’s SKIL database was released, and most recently, 2004, the NovaTech database developed by Marco Congo and Leslie Sherlin.

All qEEG databases continue to be somewhat controversial because of various perceived flaws their technical development. While some hardcore skeptics still consider qEEG or neurometric methods not yet “ready for prime time”, the expanding literature on its development and clinical use over the past 30 years has provided increasing evidence of its research, clinical and diagnostic utility.

Current Applications of qEEG:By the early 2000’s, qEEG technology is being applied in numerous research and clinical settings.A few examples include the growing number of qEEG studies ofeffects ofphysical and emotional trauma on brain electrical activity, the continued identification of neurometric subgroups of attentional and affective disorders, the use of qEEG normative databases to increase efficiency ofprescribingpsychotropic medications, and the use ofindividual brainmaps to select neurotherapy treatment protocols.

QEEG Administration: The EEG data used in qEET analysis uses the same EEG signals recorded in any professional EEG laboratory, using the International 10 – 20 Electrode Placement System (Jasper, 1958). Both standard visual analysis of the raw EEG record as well as the mathematical analysis of the digitized record are done in qEEG.Any measurement of electrical potential requires two sites. It is the differential between the two sites that constitutes the EEG measurement.The two linked ears provide the reference site for the 19 –21 head locations used in the standard brainmap.Each site is examined relative to the linked ears to determine the relative amount of power in each of the four frequency bands.

While there is no single agreed upon qEEG test battery, most of the existing databases were collected in an eyes closed, resting state as the baseline condition because it is the easiest state in which to assure good intra-subject reliability that can be compared to a norm group.However, some disorders show up only under mental challenge or when eyes are open. Therefore, more norms are needed for these conditions in the future.

Conclusions based on qEEG records are only as good as the quality of the data collected!

 
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