5.1 Normal EEG Patterns

ABRET Registered EEG Technologist R.EEG.T.

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1 Introduction & R.EEG.T. Exam Overview

1.1 R.EEG.T. Exam Facts 1.2 Eligibility & Pathways 1.3 Content Outline & Study Strategy

2 Neurophysiology & Instrumentation

2.1 Neuroanatomy & Neurophysiology 2.2 Electronics & Instrumentation 2.3 Montages & Derivations

3 Pre-Study & Patient Preparation

3.1 Patient History, Assessment & Safety 3.2 Electrode Application & the 10-20 System 3.3 Equipment Setup & Calibration

4 Performing the Study

4.1 Recording Technique & Documentation 4.2 Activation Procedures 4.3 Special Studies & Populations

5 EEG Patterns, Artifacts & Recognition

5.1 Normal EEG Patterns 5.2 Abnormal Patterns 5.3 Artifact Recognition & Elimination

6 Clinical Correlation & Seizure Disorders

7.1 Seizures, Epilepsy & Syndromes 7.2 Neonatal & Pediatric EEG Patterns 7.3 Neurological Disorders & EEG Correlation

7 Post-Study Procedures & Professional Practice

8.1 Post-Study Procedures & Documentation 8.2 Ethics, Safety & Professional Issues

8 Final Review & Test-Day Strategy

6.1 High-Yield Recap 6.2 Localization & Pattern Drills 6.3 Test-Day Strategy & Pitfalls

5.1 Normal EEG Patterns

Key Takeaways Explain This Topic AI

The posterior dominant rhythm (PDR) in a normal awake adult is 8.5-13 Hz alpha, attenuates with eye opening, and should be symmetric within 1 Hz between hemispheres.

Sleep architecture markers in order of N2 onset are vertex sharp waves, sleep spindles (12-14 Hz), and K-complexes; POSTS appear in N1-N2 over the occipital region.

Mu rhythm is a 7-11 Hz centrally located arciform rhythm that reacts to contralateral movement, not to eye opening, distinguishing it from alpha.

Benign variants such as wicket spikes, RMTD, BETS/SREDA, and 14-and-6 positive bursts mimic epileptiform activity but have no clinical significance.

The PDR matures with age: roughly 4 Hz at 4 months, 6 Hz at 12 months, 8 Hz by age 3, and reaches the adult 9-10 Hz range by about 8 years.

Last updated: May 2026

Why Normal Patterns Matter for the R.EEG.T. Exam

The single most important skill tested under the Performing the Study domain (75% of the exam) is knowing what normal looks like. You cannot reliably flag an abnormality until you have internalized the normal background for the patient's age and state of consciousness. ABRET questions frequently present a described pattern and ask whether it is normal, a benign variant, or pathologic. A technologist who calls a wicket spike "epileptiform" or a vertex wave "a sharp transient" creates a record that can mislead the interpreting physician.

This section covers four areas: the awake background, the drowsy/sleep transition and its hallmark elements, the benign normal variants that mimic epileptiform activity, and how all of these change with age.

The Awake Background: Posterior Dominant Rhythm

The posterior dominant rhythm (PDR) is the foundation of every adult EEG read. In a relaxed, awake adult with eyes closed it is an alpha rhythm of 8.5-13 Hz , maximal over the occipital and parietal regions, and it attenuates (blocks) with eye opening and returns with eye closure.

PDR Property Normal Adult Finding Why It Matters
Frequency 8.5-13 Hz (>=8.5 Hz awake) <8 Hz awake suggests encephalopathy
Reactivity Attenuates with eye opening Loss of reactivity is abnormal
Symmetry Within ~1 Hz / ~50% amplitude side to side Persistent asymmetry suggests a focal lesion
Distribution Maximal posteriorly Anterior "alpha" may be alpha coma, not normal

A normal feature often mistaken for pathology is alpha squeak (a brief frequency rise of the PDR right after eye closure) and the normal slight amplitude asymmetry favoring the right occipital region (the left is commonly a few microvolts lower).

Beta, Theta, and Delta in the Normal Record

Low-amplitude beta activity (>13 Hz) over the frontocentral regions is normal and is markedly increased by benzodiazepines and barbiturates — a medication effect the technologist should note in the recording. Scattered low-amplitude theta (4 to <8 Hz) is normal in the awake young adult, especially frontocentrally and during drowsiness. Sustained delta (<4 Hz) is not normal in the awake adult but is the dominant frequency of deep sleep and of the normal young infant.

The Drowsy-to-Sleep Transition

As the patient becomes drowsy, the PDR slows and fragments, slow lateral eye movements appear, and theta increases. Recognizing this sequence prevents the technologist from mislabeling normal drowsy slowing as focal pathology.

Sleep Architecture and Its Hallmark Elements

Sleep Stage Hallmark EEG Features
N1 (light) PDR dropout, theta, slow rolling eye movements, vertex sharp waves , POSTS
N2 Sleep spindles (12-14 Hz) and K-complexes on a theta background
N3 (slow-wave) High-amplitude (>75 uV) delta occupying >=20% of the epoch
REM Low-voltage mixed frequency, sawtooth waves, rapid eye movements, muscle atonia

Key normal transients and their correct identification:

Vertex sharp waves (V waves): Sharply contoured negative transients maximal at the Cz electrode in N1-N2. They are symmetric and do not indicate epilepsy, though they can be sharply contoured in children.

K-complexes: A high-amplitude diphasic slow wave (initial sharp negativity followed by a slower positivity) maximal frontocentrally, often followed by a spindle. They define N2 and can be evoked by a sudden sound.

Sleep spindles: 12-14 Hz sinusoidal bursts, frontocentral, lasting >=0.5 s. They appear by ~2-3 months of age and should be roughly symmetric by ~2 years.

POSTS (Positive Occipital Sharp Transients of Sleep): Triangular, surface-positive, occipital transients in light sleep; benign and frequently mistaken for occipital sharp waves.

Benign Normal Variants That Mimic Epileptiform Activity

These are the highest-yield "trick" patterns on the exam because they look pathologic but are clinically insignificant. Document them accurately; never describe them as epileptiform.

Variant Description Why It Is Mistaken Significance

Mu rhythm 7-11 Hz arciform rhythm, central (C3/C4) Looks like alpha or focal slowing Normal; blocks with contralateral movement, not eye opening

Lambda waves Surface-positive occipital sharp transients in the alert, visually scanning patient Look like occipital spikes Normal response to visual exploration

Wicket spikes 6-11 Hz arciform temporal spikes, often in trains Resemble temporal sharp waves Benign; no slow-wave aftercoming, no disruption of background

RMTD Rhythmic Mid-Temporal Theta of Drowsiness; 5-7 Hz notched temporal trains Resemble temporal seizure activity Benign; does not evolve in frequency or spread

BETS / SREDA Benign Epileptiform Transients of Sleep (small sharp spikes); Subclinical Rhythmic Electrographic Discharge of Adults Mimic epileptiform spikes / electrographic seizure Benign; no clinical correlation

14-and-6 positive bursts Arciform positive bursts at 14 Hz and/or 6 Hz, posterotemporal, in drowsiness/sleep Look like epileptiform bursts Benign, mostly in adolescents

The defining rule for distinguishing a benign variant from a true epileptiform discharge: a true epileptiform discharge disrupts the background and is typically followed by a slow wave , whereas benign variants do not perturb the ongoing background and lack an after-coming slow wave.

Age-Related Normal Patterns

The normal EEG is age-dependent, and the technologist must not apply adult norms to an infant record. Maturation of the posterior dominant rhythm is the most testable progression.

Age Expected Posterior Dominant Rhythm
3-4 months ~3.5-4 Hz reactive posterior rhythm appears
6 months ~5 Hz
12 months ~6 Hz
3 years ~8 Hz (reaches adult lower limit)
8 years and older ~9-10 Hz (adult range)

Other normal age-related findings the technologist should expect rather than flag:

Neonatal patterns: discontinuous tracé alternant in quiet sleep of the term newborn and tracé discontinu in the premature infant are normal for age.

Hypnagogic hypersynchrony: high-amplitude rhythmic 3-5 Hz activity at drowsiness onset in children ages ~3 months to 12 years — normal, not a spike-wave burst.

Posterior slow waves of youth: delta intermixed with the PDR posteriorly in children and adolescents; suppresses with eye opening; benign.

Elderly: mild temporal theta and slight PDR slowing toward the lower alpha range can be a normal variant of aging if reactive and not focal.

Clinical Application

When you describe a record, anchor every statement to age and state: "awake, eyes closed, symmetric 10 Hz PDR that attenuates with eye opening; drowsiness with vertex waves and POSTS; benign wicket spikes in the left temporal region without background disruption." That phrasing demonstrates the exact pattern-recognition discipline ABRET tests.