Patient guide · Clinical neurophysiology
Electroencephalogram (EEG), what to expect from your brain-wave test — standard, sleep-deprived, ambulatory and video.
The electroencephalogram (EEG) records the electrical activity of your brain from scalp electrodes. This detailed patient guide explains what to expect from each protocol — standard, sleep-deprived, ambulatory and video-EEG — and how results guide next steps.
Key facts
- 01
Definition
Scalp recording of cerebral electrical activity from surface electrodes.
- 02
Painless standard test
A routine EEG takes 30–60 minutes and involves no needles or radiation.
- 03
Sleep-deprived EEG
Increases diagnostic yield in suspected epilepsy by capturing drowsy and sleep states.
- 04
Ambulatory EEG
A 24–72 hour take-home recording, best when events are infrequent.
- 05
Video-EEG
Time-locked video and EEG — the reference standard for nocturnal and non-epileptic events.
- 06
Reported by a specialist
Every trace is read by a consultant clinical neurophysiologist.
Preparation and diagnosis pathway
From referral to report — what happens, in order.
The route is the same across the four EEG protocols — the differences are in how long you record for, and whether video is time-locked to the trace.
- 01
Before
Neurology consultation
A clinician confirms the clinical question — epilepsy work-up, encephalopathy, nocturnal events or prognostication — and chooses the right EEG protocol.
- 02
Before
Wash hair without conditioner
Clean, dry, product-free hair helps the electrodes make good contact and shortens set-up time.
- 03
Before
Sleep-deprived overnight if asked
For a sleep-deprived EEG you may be asked to stay awake all or part of the previous night — increases seizure detection.
- 04
On the day
Scalp electrodes applied
A physiologist places 20–25 electrodes using the international 10–20 system, secured with a mild paste.
- 05
On the day
Photic stimulation and hyperventilation
Standard activation procedures — a flashing strobe and 3 minutes of deep breathing — provoke and unmask abnormal patterns.
- 06
On the day
Video-EEG monitored if requested
Time-locked video allows the neurophysiologist to correlate any clinical event with the electrical trace.
- 07
After
Structured neurophysiology report
A consultant clinical neurophysiologist issues a written report with impression and recommended next step.
What it shows
What the EEG can — and can’t — answer.
The EEG is a functional test, not an anatomical one. It reads electrical activity in real time — well suited to epilepsy, encephalopathy and coma questions, and complementary to MRI.
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Epileptiform discharges
Spikes, sharp waves and spike-and-wave complexes that support a diagnosis of epilepsy.
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Focal or generalised slowing
A regional or diffuse slowing of background activity — a marker of structural or metabolic disturbance.
-
Encephalopathy pattern
Diffuse slow-wave activity or triphasic waves suggesting a systemic or toxic-metabolic cause.
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Photoconvulsive response
An abnormal response to photic stimulation — a hallmark of photosensitive epilepsy.
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Nocturnal seizure activity
Video-EEG captures events that occur only during sleep, distinguishing seizure from parasomnia.
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Non-epileptic events
Video-EEG can demonstrate that clinical events are not accompanied by ictal EEG change — a positive diagnosis.
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Coma prognostication
Background reactivity and burst-suppression inform prognosis after cardiac arrest or severe brain injury.
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Red flag: status epilepticus on EEG — urgent admission
Continuous ictal discharges are a neurological emergency — call 999.
Next steps
What the report unlocks.
The EEG is a step, not an endpoint. These are the pathways the report typically opens up — medication changes, longer recordings, imaging, and specialist review.
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Anti-seizure medication
Initiation, adjustment or switch based on epileptiform findings and event type.
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Video-EEG for pre-surgical evaluation
Prolonged inpatient recording to localise the seizure focus before epilepsy surgery.
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Sleep-medicine referral
When events look like a parasomnia rather than a seizure, formal sleep assessment is the next step.
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Ambulatory EEG for infrequent events
24–72 hour take-home recording to capture rare or nocturnal episodes.
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MRI brain
Structural imaging to look for a lesion that explains focal EEG change.
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Neurology follow-up
Consultant review to translate the report into a management plan.
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Multi-disciplinary team review
Complex or surgical cases discussed at a specialist epilepsy MDT.
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Driving-restrictions advice
Clear guidance on DVLA notification and driving restrictions after a seizure or suggestive EEG.
Red flags
When an EEG finding is urgent.
Some EEG patterns are neurological emergencies in their own right. These are the ones the reporting neurophysiologist will flag immediately.
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Status epilepticus
Continuous or rapidly recurring seizure activity — a neurological emergency requiring urgent admission.
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Non-convulsive status
Ongoing ictal EEG without overt convulsion — often presents as unexplained confusion or reduced consciousness.
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Sub-clinical seizures
Ictal discharges without a visible clinical event — common in critical care and after brain injury.
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Encephalitis pattern
Focal slowing with epileptiform discharges (e.g. temporal PLEDs) raising concern for herpes simplex or autoimmune encephalitis.
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Creutzfeldt–Jakob triphasic waves
Periodic sharp-wave complexes that, in the right clinical setting, prompt urgent prion-disease work-up.
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Coma with poor prognostic features
Burst-suppression, absent reactivity or alpha-coma patterns after hypoxic-ischaemic injury.
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SUDEP risk features
Frequent generalised tonic-clonic seizures and nocturnal events increase sudden-death risk — a driver for escalation.
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Autoimmune encephalitis
Extreme delta brush and other stereotyped patterns should prompt antibody testing and immunotherapy review.
-
New-onset focal seizures
A first focal seizure with an EEG correlate warrants urgent structural imaging and specialist review.
Reading your report
An EEG report can look intimidating. It isn’t.
Whatever the finding, the report keeps to the same four parts.
A quiet reminder
The report is written for your doctor, not for you — and that’s normal.
If you would like us to talk you through it before your follow-up, just ask.
- 01 Header
Clinical question and protocol
Your details, the referring question, and whether this is a standard, sleep-deprived, ambulatory or video-EEG.
- 02 Technique
Recording set-up and activation
Electrode montage, recording duration, and which activation procedures (photic stimulation, hyperventilation) were performed.
- 03 Findings
Background, transients and events
Description of background rhythms, any epileptiform or slow-wave abnormalities, and correlation with any clinical events on video.
- 04 Impression
The conclusion: read this first
Whether the EEG is normal or abnormal, the likely significance, and the concrete next step — read this first.
Frequently asked
Everything patients ask us about EEG.
Quick answers on protocol choice, medication, timing, and when video-EEG is needed instead of a standard recording.
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What can an EEG actually tell me — and when do I need one?
An EEG records the brain’s electrical activity from scalp electrodes and shows the background rhythm, any epileptiform spikes and sharp waves, and focal or generalised slowing that hints at a structural, epileptic or metabolic cause. In London it’s usually requested after a first seizure, unexplained blackouts or possible absence episodes, and we can typically arrange a consultant-reported study within 5–10 working days.
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What is the difference between a standard, sleep-deprived, ambulatory and video-EEG?
A standard EEG is a 30–60 minute recording in the department. A sleep-deprived EEG asks you to stay awake overnight to increase the chance of capturing abnormal activity. An ambulatory EEG is a 24–72 hour take-home recording for infrequent events. A video-EEG adds time-locked video and is the reference standard for nocturnal and non-epileptic events.
-
Is an EEG painful?
No. Electrodes are stuck to the scalp with a mild paste — there are no needles, no radiation and no electric current going into your head. The recording only reads the brain’s own signals.
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Do I need to stop my medication?
Do not stop anti-seizure medication without your neurologist’s explicit instruction. Some protocols ask for a temporary reduction to increase yield, but that decision belongs to the referring clinician.
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How quickly will I get results?
A written report from the reporting consultant clinical neurophysiologist is typically issued within 3–7 working days — sooner for urgent studies flagged by your neurologist.
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When is a video-EEG needed instead of a standard EEG?
Video-EEG is the right test when events happen mostly at night, when the diagnosis of epilepsy is uncertain, when non-epileptic attacks are suspected, or as part of a pre-surgical work-up. A standard EEG cannot answer those questions on its own.
Sources and further reading
Guidelines behind this page.
Reviewed 2026-07-30 · Next review 2027-07-30
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NICE. Epilepsies in children, young people and adults (NG217).
Visit source -
British Society for Clinical Neurophysiology. Guidelines and standards.
Visit source -
International League Against Epilepsy. Guidelines and classification.
Visit source -
American Clinical Neurophysiology Society. Guidelines for EEG.
Visit source
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In practice, in London
Where electroencephalogram EEG sits in a private London pathway
With electroencephalogram EEG, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. Waiting lists on the NHS for electroencephalogram EEG vary widely by borough and by how the GP letter reads. Privately in London, we can normally offer a slot inside the same week, sometimes within 48 hours if there’s a cancellation. The difference isn’t clinical quality — the consultants are frequently the same faces you’d see on the NHS — it’s the calendar.
Once you’re in the private system for electroencephalogram EEG, the pace picks up noticeably. Consultant slots run to time, imaging is usually available in the same building or a short walk away, and the report comes back typed and detailed. It’s the coordination that tends to feel different — one person on the other end of the phone, not a switchboard. For electroencephalogram EEG specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
We’re careful about what a private pathway for electroencephalogram EEG can and can’t promise. It can compress a wait, put you in front of a subspecialist quickly, and get a proper report in your hands within a week. It can’t rewrite what the imaging or the bloods say. Setting that expectation up front tends to make the whole experience less stressful.