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300 Longwood Avenue
Boston, MA 02115
(617) 355-6000
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My Child Has:
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Quantitative EEG
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A qEEG, or quantitative EEG, adds modern computer and statistical analyses to traditional EEG and EP studies.
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An EEG is an important test used worldwide to detect neurological abnormalities. It is primarily used to evaluate epilepsy, but may be recommended for other neurological problems such as headaches, behavioral disturbances, attention disorders, learning problems, language delay, developmental delay, and fainting spells. EEGs for children were first developed and used at Children's Hospital Boston.
An EEG, also referred to as a "brain wave" test, records the ever-present, ongoing electrical activity generated by the neurons in the brain EEG and EP studies both measure brain activity. (EEG measures the brain while a child is resting or sleeping, whereas EP studies measure brain activity when different parts of the brain are stimulated.) Abnormal signals in these tests include little electrical "explosions" such as the spikes, spike and wave, and sharp waves that are common in epilepsy even when children are not in the midst of a clinical seizure.
Normally, doctors evaluate EEGs just by looking at the pattern of spikes and waves. However, a qEEG can provide a more detailed analysis in measuring brain waves. Because results may be graphically displayed on a schematic map of the head, the procedure is often called Brain Electrical Activity Mapping (BEAM) or simply "mapping." In that sense, qEEG should be viewed as an extension of (not a replacement for) traditional EEG. Patients undergoing a qEEG also have a traditional EEG taken, since the human eye is still superior to the computer in many aspects of brain signal analysis.
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From the patient's perspective, the procedure is nearly identical to the EEG and EP. Electrodes are painlessly placed on scalp in order to measure electrical activity. For a qEEG, about 50 percent more electrodes are applied than for an EEG or EP. The extra electrodes help define in more detail the different parts of the brain, and they collect about twice as much data as a traditional EEG. This makes it possible to analyze the brain waves more comprehensively.
A patient has both resting (EEG) and stimulated (EP) brain activity monitored. The results are first read traditionally, by visual inspection. Afterward, computers can perform a variety of statistical analyses and compare a patient's results to a database of brain electrical activity.
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Doctors often request a qEEG when they believe that a patient's brain function is abnormal but have trouble defining the cause. Typical referrals include patients of all ages (newborns to adults) with:
- seizures
- epilepsy (especially to better determine the epileptic source)
- Landau-Kleffner Syndrome (when treatment is being considered)
- unexplained developmental delay or intellectual decline (suspected dementia)
- learning disability and/or attentional deficit disorder (to better determine the cause)
- behavioral dysfunction or emotional illness (including unremitting headaches) when a biological cause is suspected
- chronic fatigue syndrome
- whenever the EEG would be expected to show something but does not
Often, a qEEG helps doctors make a diagnosis and evaluation because it can analyze data more complexly than visual inspection can. The following are some analyses that quantitative EEGs have made possible.
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One of the most useful applications of a qEEG is spectral analysis and mapping, where the different levels of electrical activity in the brain are "mapped" using colored 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.
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Some illnesses may begin with abnormalities of cortical coupling, the correlation in brain activity between cortexes of the brain. Researchers have linked such abnormalities to disorders such as Alzheimer's disease and even closed head injuries.
By mapping brain activity (called spectral analysis), a qEEG can measure the coherence between two electrodes. It assesses the similarity of brain activity of two electrodes over time, a measure of "coupling" between brain regions. This type of analysis (spectral coherence) is virtually impossible to estimate by visual EEG inspection.
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Statistical probability maps (SPM) help determine if spectral data are outside of the normal bounds for a patient's age. By detecting abnormal spectral data from a qEEG, a qEEG can map not only a patient's brain activity, but how much it deviates from what is considered "normal." These images of deviancy are referred to as SPM (statistical or significance probability maps). With these maps, doctors can identify the areas of a patient's brain that are causing the issue by identifying abnormal regions on the SPM.
QEEG techniques like SPM make it much easier to detect subtle changes or abnormalities in brain activity. For example, a qEEG can show if a patient's brain is "encephalopathic," which means that it has excessive EEG slowing. QEEG techniques can determine whether behavioral disturbance in an adult is due to early dementia (increased slowing) or otherwise uncomplicated depression (no increase of slowing). Although developed first for qEEG analyses, the SPM technique has been widely adapted for use with other neuroimaging techniques.
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Another area where qEEG techniques have been applied is to the long latency sensory evoked potentials. Normally, an EEG measures the brain's ongoing electrical activity while the patient is resting. However, doctors can also assess the brain's response to externally applied stimuli - such as light flashes, auditory clicks, and mild electrical shocks -- with "evoked potentials" (EPs). EP data is used to test for many common conditions, when doctors suspect that the cause is in the patient's brain cortex. For example, EP data is often used in evaluating dyslexia, schizophrenia, Alzheimer's disease, and epilepsy.
For EP testing, a patient is not constantly exposed to stimuli (a sound, light flash, etc.), but also has periods of "waiting time" in between the exposures. Therefore, EP data (when the brain is exposed to stimuli) is mixed in with intervals of EEG data (when the brain is just resting). One difficulty of evaluating a patient's response to stimuli is separating these two types of data, especially when the stimulus exposure is long. With a qEEG, however, statistical analysis can "sift out" the EP data.
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Discriminant analysis is used to asses whether or not data belongs to a statistical "population." When it is applied to qEEG data, discriminant analysis can help determine if a patient has a specific disorder (e.g., head injured or not, dyslexia or not, bipolar vs. monopolar depression, etc). However, these tests are more widely used for psychiatric than neurologic issues.
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One of the most effective treatments for patients with epilepsy is surgical removal of the part of the brain causing seizures, called the "epileptic focus." If the focus is properly located and removed, seizures will stop and patients can continue a normal life without any loss of brain function. For epilepsy patients, a qEEG can calculate, from simple scalp recorded segments containing epileptic spikes, the location of the epileptic focus.
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The information on this website should not be taken as medical advice,
which can only be given to you by your personal health care professional. |
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Copyright © Children's Hospital Boston. All rights reserved. |
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