What Does an ADHD Brain Scan Actually Show You?

You've booked a brain screening. Or you're thinking about it. Either way, the question is the same: what will the report actually tell you?

The honest answer is that it tells you quite a lot — but only if you understand what the numbers mean. A theta/beta ratio of 4.2 with a z-score of 2.1 at Cz is powerful clinical data. It's also completely meaningless if nobody explains it.

This article walks through every section of the report in plain English. No jargon without explanation. No numbers without context. By the end, you'll be able to read your own report — or anyone else's — and understand exactly what the brain data is saying.

The report at a glance

Your professional PDF report contains four main sections, each answering a different question about your brain:

Resting-state EEG data — what is your brain doing when you're sitting quietly? This captures your baseline brain activity across five frequency bands at four electrode sites. It reveals whether your brain's electrical signature matches the patterns seen in published ADHD research.

Theta/beta ratio analysis — is your brain under-aroused? This is the headline number — the single most-studied EEG biomarker for ADHD, measured at the same cortical site (Cz) referenced by the FDA. It's the ratio that started the entire field of quantitative EEG assessment for ADHD.

Go/No-Go attention task results — how does your brain perform under cognitive load? This 3-minute computerised task measures sustained attention, impulse control, and response consistency. It captures the behavioural side of ADHD in quantified, comparable data.

Normative comparison — how do you compare against published research? Every measurement is expressed as a z-score against age-matched data from 311 research subjects across six peer-reviewed studies. This is what makes the data clinically meaningful — it's not "your brain activity" in isolation, it's "your brain activity compared to what's expected for your age."

Where we measure: the four electrode sites

The brain is not uniform. Different regions handle different functions, and ADHD affects some regions more than others. We measure at four carefully chosen sites on the international 10-20 system — the standardised electrode placement framework used in clinical neuroscience worldwide.

These four sites capture the cortical regions most relevant to ADHD neuroscience. More electrodes would add resolution but not fundamentally change the clinical picture — the theta/beta ratio at Cz alone carries the strongest research backing for ADHD screening.

The five frequency bands

Your brain produces electrical activity across a continuous spectrum of frequencies. Neuroscientists divide this spectrum into five named bands, each associated with different brain states:

Your report shows the absolute and relative power in each band at each of the four electrode sites. Absolute power tells you the raw amplitude of activity. Relative power tells you what proportion of total brain activity falls in each band. Both are clinically informative, and both are compared against published norms.

The theta/beta ratio — the headline number

The theta/beta ratio (TBR) is the single most important number in the report. It's calculated by dividing theta power by beta power at Cz — the central vertex, directly over the sensorimotor cortex.

A higher TBR means relatively more slow-wave (unfocused) activity compared to fast-wave (focused) activity. In ADHD, the TBR is consistently elevated across hundreds of independent studies spanning three decades. The brain is producing too much theta and not enough beta — the neural circuitry that supports sustained attention is under-powered.

The TBR varies naturally by age — children have higher ratios than adults because the brain matures over time, producing relatively less theta as it develops. This is why age-matched comparison is essential. A TBR of 4.5 might be elevated for a 35-year-old but perfectly normal for a 7-year-old. Our report compares your TBR against published norms for your specific age group, ensuring the comparison is meaningful.

Z-scores: what the numbers actually mean

Every key measurement in the report is expressed as a z-score — a statistical measure that tells you how far your result sits from the average for a reference population. Z-scores are the universal language of clinical measurement. They're used in blood tests, growth charts, IQ scores, and every other domain where individual measurements need to be compared against population norms.

A z-score of 0 means your measurement is exactly at the average for your age group. A z-score of 1.0 means you're one standard deviation above average — higher than about 84% of the reference population. A z-score of 2.0 means you're two standard deviations above average — higher than about 98% of the reference population. This is generally considered the threshold for clinical significance.

When your GP sees a z-score of 2.3 on your theta/beta ratio, they don't need to understand qEEG methodology. They understand z-scores — it's the same framework they use every day for blood work and developmental milestones. A number that sits 2.3 standard deviations above the mean is noteworthy in any clinical context.

The Go/No-Go attention task

While the resting-state EEG captures what your brain does at baseline, the Go/No-Go task captures what it does under cognitive load. This 3-minute computerised test presents a rapid series of stimuli — green circles (press the button) and red squares (don't press) — and measures four key metrics:

These four metrics are quantified, comparable, and clinically meaningful. They capture the same constructs that ADHD questionnaires try to assess through subjective observation, but they measure them directly. A miss rate of 34% is more informative than a teacher ticking "often fails to give close attention to details."

Common patterns and what they suggest

Most reports show one of several recognisable patterns:

Classic ADHD pattern

Elevated theta, reduced beta, high TBR at Cz. This is the textbook ADHD profile — cortical under-arousal at the vertex. The Go/No-Go task typically shows elevated miss rates and high reaction time variability. This pattern is the most robustly supported by published research and the most responsive to stimulant medication.

ADHD with anxiety

Elevated theta AND elevated alpha. The theta indicates ADHD-pattern cortical under-arousal. The alpha indicates concurrent anxiety or rumination. This co-occurring pattern is extremely common — particularly in women and girls — and is clinically important because it affects treatment decisions. Stimulants may help the attention deficit but could initially increase anxiety.

Predominantly inattentive

Elevated theta with normal or low false alarms on Go/No-Go. The brain is under-aroused (inattentive type) but impulse control is intact. These individuals are the daydreamers, not the disruptors. They're systematically missed by teacher questionnaires because they don't cause problems in class — they just silently fall behind.

Predominantly hyperactive-impulsive

High false alarm rate, high reaction time variability, with near-normal TBR. Less common in isolation. The brain data may show a different pattern — elevated frontal beta or asymmetric prefrontal activity. These cases benefit from clinical consultation to interpret the nuances.

Normal pattern

All z-scores within normal range. This happens. Not everyone who suspects ADHD has ADHD. A normal result is valuable information too — it redirects investigation toward other explanations (anxiety, sleep disorders, processing difficulties, burnout) and avoids unnecessary medication. Knowing you don't have an ADHD brain pattern is just as useful as knowing you do.

What the scan does NOT show

Transparency matters. Here's what the brain screening cannot do:

It does not diagnose ADHD. ADHD diagnosis requires a qualified clinician who considers brain data alongside developmental history, clinical interview, and behavioural observation. The screening provides one critical piece of the puzzle — the neurological evidence — but not the whole puzzle.

It does not detect structural abnormalities. Unlike an MRI, qEEG does not image brain structure. It measures function — electrical activity — not anatomy. It won't detect tumours, lesions, or structural differences.

It does not predict medication response. While elevated TBR is associated with positive stimulant response in research, individual medication decisions must be made by a prescribing clinician. The medication comparison scan can track whether medication has changed your brain activity, but the baseline scan alone cannot predict which medication will work.

It does not replace clinical judgment. The data is powerful, objective, and clinically meaningful. But it is data, not a diagnosis. The best outcomes come from brain data plus clinical expertise — which is why our comprehensive assessment includes a clinical consultation that contextualises the findings.

Common questions

Related: The full science · How the screening works · Results explained · qEEG vs questionnaire · Medication comparison scan