Think of a cardiac assessment. When a doctor performs an ECG (electrocardiogram), they record the heart’s electrical activity — not a structural image of the heart, but its electrical function. QEEG works on the same principle, with the brain as the subject.

What Is QEEG?

QEEG — Quantitative Electroencephalography — is the recording and quantitative analysis of the brain’s electrical activity. The assessment uses 19 to 32 electrodes attached to the scalp via a specialised cap and conductive gel. These electrodes do not transmit any electrical current to the brain — they only read the signals that neurons naturally produce.

What distinguishes QEEG from conventional EEG is its quantification. A standard EEG is interpreted visually by a clinician looking for abnormal patterns such as epileptiform discharges. QEEG takes an additional step: signals are subjected to mathematical transformation (Fast Fourier Transform) to measure the relative strength of different brain-wave frequencies at each recording point.

Brain Waves: What Is Actually Being Measured?

The brain produces electrical signals across a range of frequencies, classified into frequency bands:

Band	Range	Clinical Associations
Delta	0.5–4 Hz	Deep sleep; excess when awake: indicator of damage or dysfunction
Theta	4–8 Hz	Drowsiness, memory; excess cortical theta: associated with ADHD, slow cognition
Alpha	8–13 Hz	Relaxed alertness, cortical idling; alpha deficits: anxiety, trauma
Low Beta	13–18 Hz	Active focus, decision-making
High Beta	18–30 Hz	High alertness; excess: stress, anxiety, rumination
Gamma	>30 Hz	High-level sensory processing, perceptual binding

QEEG produces topographic maps — colour-coded representations of each band’s distribution across the scalp surface. This allows identification of areas showing activity outside normative limits.

Coherence: Connectivity Between Brain Regions

Beyond frequency power, QEEG also measures coherence — how coordinated the activity is between two different brain locations. Coherence that is too low indicates areas working too independently (weak functional connectivity). Coherence that is too high can indicate maladaptive hypersynchronisation.

Abnormal coherence patterns have been identified in various neurological and psychiatric conditions, including autism, ADHD, brain trauma, and post-stroke recovery (Newson & Thiagarajan, 2019; Thatcher et al., 2015).

How Is the Assessment Performed?

Preparation: clean, dry hair (no conditioner or hairspray)
Setup: EEG cap with electrodes placed on the scalp using conductive gel. This takes 10–15 minutes.
Recording: You sit comfortably, eyes open for a few minutes then closed. Total recording time is approximately 20–30 minutes.
Analysis: Raw data is processed computationally to extract power spectra and coherence values.
Interpretation: Results are compared against a normative database to identify clinically meaningful deviations.

The assessment is completely painless and involves no radiation or magnetic fields.

QEEG’s Role in Guiding Neuromodulation

This is where QEEG’s clinical value is most significant. Without an objective brain-activity map, neuromodulation protocols (such as transcranial electrical stimulation or neurofeedback) must be based on assumptions or general guidelines derived from diagnosis alone.

With QEEG:

Stimulation targets can be determined individually, based on specific dysfunction patterns
Neurofeedback protocols can be designed to train the frequencies and locations genuinely relevant for that patient
Progress can be tracked objectively — not relying solely on subjective patient reports

Like a navigator planning a route from an accurate map, QEEG provides data-driven guidance for more precise interventions.

Who Might Benefit from QEEG?

QEEG is most relevant for:

Patients preparing to begin a neuromodulation programme (neurofeedback, TES)
Post-stroke recovery with persistent cognitive or motor deficits
Mild cognitive impairment (MCI) and early-stage dementia assessment
Attention and learning difficulties that have not responded to standard interventions
Epilepsy as a complement to conventional EEG evaluation

Note: This article is educational and does not constitute a medical service offer. Please consult a qualified physician regarding your specific assessment needs.

References:

Thatcher RW et al. (2015). Normative QEEG databases and clinical applications. Clinical EEG and Neuroscience, 46(2), 71-72.
Newson JJ & Thiagarajan TC (2019). EEG frequency bands in psychiatric disorders: a review of resting state studies. Frontiers in Human Neuroscience, 12, 521.
Salinsky MC et al. (2020). Quantitative EEG in neurological practice: a review. Epilepsia, 61(4), 614-626.