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QEEG

A QEEG is a computer analysis of the raw EEG signal which is recorded using 19 or more channels simultaneously. The quantitative EEG (qEEG) applies sophisticated mathematical- and statistical analysis to highlight specific waveform components and to compare them to age and gender-controlled databases (compiled from the EEGs of individuals with no known brain dysfunction).

The processed EEG is converted into coloured brain maps or topographical maps which can also be called a functional EEG as seen below. Topographical maps provide a convenient schematic representation of the results of the spectral analysis of a report from an EEG signal. 

The EEG is transformed to a functional qEEG and the process is illustrated below:

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The QEEG metrics derived from the EEG signal includes:

  • Absolute Power: The actual power (voltage) in the client’s EEG and its distribution across the brain. Delta: 1 – 3 Hz Theta: 4 – 7 Hz Alpha: 8 – 12 Hz Beta: 13– 25 Hz ; Hibeta > 25Hz.

  • Frequency Ratios (such as Theta/Beta; Alpha/Theta; etc.): They can be slow-to-fast relationship measurements or fast-to-slow.

  • Relative Power: The percentage of power in any band compared with the total power in the client’s EEG (e.g., “relative theta” is the percentage of theta of the combined sum of delta, theta, alpha, and beta).

  • Z Scores of the power: The Z score value indicates how “deviant” a client’s score is from the norm and indicates whether there is deficient or excessive activity in each frequency for a given electrode site.

 

  • Coherence: Communication, coordination, and connection between two cortical areas of the brain. Coherence focuses on Hyper (excessive) or Hypo (too little) connectivity between two sites.

 

  • Phase:  A measure of the temporal relationship between two signals. It reflects the speed of information sharing between sites. The speed of communication may be too slow (increased phase lag) or too fast (reduced phase lag).

 

  • Peak frequencies of the EEG within a frequency band. For example, the alpha band is defined as 8 – 12 Hz. The frequency measure indicates whether the patient’s alpha frequency is slow (closer to 8 Hz.) or fast (closer to 12 Hz.).

  • Symmetry: The right-left and front-back balance in power of the raw EEG signal.

Depending on the specific database, metrics available to the QEEG practitioner may vary.

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The reasons for requesting a QEEG may include, but are not limited to:

  • Identifying patterns of brain wave dysfunction that may be related to a variety of problems, such as learning and behavioural issues, emotional disorders, brain injury, and many others.  

  • Facilitating sensor placement and treatment protocol choices for brain training modalities for instance  Neurofeedback training and other brain-based modalities such as transcranial magnetic stimulation, vielight etc. to facilitate learning and self-regulation.

  • Guiding clients who are involved in a process of brain regulation through their journey by providing pre-and-post QEEG assessment information of changes in brainwave activity.

  • Supporting qualified healthcare practitioners like medical doctors, functional and integrative practitioners, Occupational therapists as well as other health-based disciplines to make informed decisions about psychotherapy, medication, functional medicine, supplements, forensic investigation, etc.

Frequently asked questions are related to the interaction and interplay between the EEG, Neurofeedback, and QEEG fields.

  • Commonalities between an EEG and a functional QEEG:

  • The physiological bases of these disciplines rely on common ground. All practitioners agree that the scalp EEG is produced by the postsynaptic membrane polarization of pyramidal cells. A standard electroencephalogram (EEG) records electrical activity or brainwaves that are representative of underlying cortical brain activity. Both the EEG and qEEG provide valuable information about real-time functioning within the brain at the time of evaluation.

  • Differences between an EEG and a functional QEEG:

  • Clinical electroencephalography (EEG) and quantitative EEG (QEEG), despite their common underpinnings in electrophysiology and instrumentation, have different origins, histories, and priorities. These differences are exemplified in practice by the fact that generally, EEG practitioners (Neurologists, Neurophysiologists) do not use QEEG (and may not even be aware of it). They use an EEG for diagnostic purposes. A QEEG on the other hand is used to compare functionality from various perspectives to a normed database, often to provide recommendations for Neurofeedback training.

Confusion in this domain is easily explained in the diagram below.

Summary:

 

The fields of EEG, QEEG, and Neurofeedback exist as 3 separate disciplines, although there are overlaps between these fields.  In the world of practitioners, these three worlds can be applied individually or used as two methods together, while only a small number of practitioners are competent in and use all 3 areas.

Clinical EEG and Neuroscience 2021, Vol. 52(2) 79–81 © EEG and Clinical Neuroscience Society (ECNS) 2021 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1550059421993957 journals.sagepub.com/home/eeg.

 

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