What is qEEG?
qEEG, or quantitative EEG, began in the 1970s and early 80s as an attempt to extract from brain electrical activity more information than the normal visual inspection of EEG, which Neurologists analyse. Thus a qEEG should be viewed as an extension of and not a replacement for traditional EEG. Because results may be graphically displayed on a schematic map of the head, the procedure is often called a “Brain Map” Both resting (EEG) and stimulated (EP) data are recorded and are analysed by Professor Kropotov of The Institute for Human Brain Potential. All aspects of brain activity are statistically compared to a database of brain electrical activity recorded on normal healthy children and adults. Other special groups such as Dyslexia, Attention Deficit Disorder, Dysgraphia, Depression etc., have also been grouped in the data base to show particular patterns associated with the problem. Age is important as certain processes (for example Evoked Potentials) show typical slowing in processing of stimuli in many types of Specific Learning Disability as well as aging and memory loss. Special Evoked Potential activation stimuli are available to suit special issues (e.g., Dyslexia or ageing).
Another area where qEEG techniques have been applied is to the long latency sensory evoked potentials. EEG represents the brain’s ambient, spontaneously ongoing electrical activity. Evoked potentials (EPs) are the brain’s transient response to externally applied stimuli – such as light flashes and auditory clicks. These stimuli form, respectively, the visual evoked response or potential (VEP), auditory EP (AEP) Classic neurophysiology employs a few EP channels and evaluates the short latency response (e.g., under 30 milliseconds).
When obtained these signals are seen to arise from specific deep brain structures and allow for assessment of structures within the brain stem and thalamus. When longer latencies (longer times from stimulation) are evaluated, signals appear to be coming from the cortical mantle.
Unfortunately the complex waveform morphologies from a large set of such long latency EPs can be very difficult to analyse by unaided visual inspection. However with the use of normative databases clinically important abnormality can be delineated within the complex combined spatial-temporal information collected by Evoked Potentials. Thus developmental delay or intellectual decline (suspected dementia); emotional instability/illness or learning disability and/or attentional deficit disorder can be better diagnosed than using subjective interviews or inconclusive psychometric testing..
But it is not only diagnosis that the qEEG is useful for. When it varies from the normal brain activity (decided from 1. the data base and 2. Professor Kropotov’s experience in deciding which is the brain activity of most relevance to the particular client) the aim is to normalise the brainwaves and their interactions by Neurofeedback. This is not always as simple as up or down training aberrant brain waves.
Clinical judgements are made according to the clients previous history, their personality, which area, frequency and amplitude would be most efficient to train for that particular abnormality.
A qEEG records brain activity in time so is a closer approximation of real time activity than brain imaging based on spatial information – i.e. where a particular lesion or injury may be in the brain, such as a PET or SPECT scan. It is an interaction of cortical and subcortical brain activity Usually a person with a specific learning or emotional disability will not have any brain area dysfunction but they may show their difficulty in terms of lack of interaction of brain waves, or insufficient power in their brain waves when they prepare for a particular task, such as reading or maths.
To assist in the estimation of EEG spectral content (one of the most difficult tasks by visual inspection), EEG data are entered into a computer, and spectral content is determined by the use of techniques of mathematical signal analysis (typically by the FFT or Fast Fourier Transform algorithm). One of the first problems was how to visualize results since qEEG typically uses more channels than EEG. The solution was to map the results using coloured grey scaling on schematic maps of the head. To some, such brain electrical activity mapping or simply “mapping” is taken as synonymous with qEEG. However mapping is only a display technique and only the first step. The heart of qEEG lies with the underlying computerized analytic and statistical techniques. Spectral Coherence
A special results of spectral analysis is the measure of coherence between two electrodes. It assesses the similarity of spectral content of two electrodes over time and is usually taken to reflect a measure of “coupling” between brain regions. It is virtually impossible to estimate coherence by visual EEG inspection. Some illnesses may begin with abnormalities of cortical coupling. Several clinicians have reported such abnormalities in Alzheimer’s disease and others have found abnormality of coherence as the best discriminator of mild closed head.