Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants PDF

electroencephalography An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants Erik K. St. Louis, MD Mayo Clinic College of Medicine, Rochester, Minnesota Lauren C. Frey, MD University of Colorado, Denver, Colorado...

electroencephalography An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants Erik K. St. Louis, MD Mayo Clinic College of Medicine, Rochester, Minnesota Lauren C. Frey, MD University of Colorado, Denver, Colorado www.AESNET.org  Electroencephalography Electroencephalography (EEG): An Introductory Text and Atlas of Normal and Abnormal Findings in Adults, Children, and Infants Editors Erik K. St. Louis, MD Mayo Clinic College of Medicine, Rochester, Minnesota Lauren C. Frey, MD University of Colorado, Denver, Colorado Contributors Jeffrey W. Britton, MD Mayo Clinic College of Medicine, Rochester, Minnesota Lauren C. Frey, MD University of Colorado, Denver, Colorado Jennifer L. Hopp, MD University of Maryland, Baltimore, Maryland Pearce Korb, MD University of Colorado, Denver, Colorado Mohamad Z. Koubeissi, MD, FAAN, FANA George Washington University, Washington, District of Columbia William E. Lievens, MD University of Alabama, Birmingham, Alabama Elia M. Pestana-Knight, MD Cleveland Clinic Foundation, Cleveland, Ohio Erik K. St. Louis, MD Mayo Clinic College of Medicine, Rochester, Minnesota Staff Executive Director: Eileen M. Murray, MM, CAE Project Manager: Jessica A. Daniels, MNA Publishing Manager: David Burns, Allen Press, Inc, Lawrence, KS ISBN: 978-0-9979756-0-4 Copyright ©2016 by American Epilepsy Society 135 S. LaSalle St., Suite 2850, Chicago, IL 60603 Care has been taken to confirm the accuracy of the information presented and to describe generally accepted practices. However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, express or implied, with respect to the contents of the publication. This text is designed to assist clinicians by providing a framework for evaluating and treating patients. It is not intended to estab- lish a community standard of care, replace a clinician’s medical judgment, or establish a protocol for all patients. The clinical condi- tions contemplated by the text will not fit or work with all patients. Approaches not covered here may be appropriate. The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accordance with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precau- tions. This is particularly important when the recommended agent is a new or infrequently employed drug. Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice. 1 Electroencephalography License Except where indicated, this publication is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License (BY-NC-SA: http://creativecommons.org/licenses/by-nc-sa/4.0/legalcode). No permission is required from the editors, authors, or publisher to reuse or repurpose content, provided the original work is properly cited. Figures, tables, and images included in this work are also published under the CC BY-NC-SA license and should be properly cited when reused or repurposed. For any reuse or redistribution of a work, you must also make clear the license terms under which the work was published. You may not apply legal or technological measures that legally restrict others from doing anything the license permits. Using Content, Including Figures, Tables, and Images Notifications of re-use should be directed to [email protected]. Where indicated, image and figure re-use permission requests should be directed to the Mayo Foundation for Medical Education and Research. Attribution This publication is provided by the American Epilepsy Society (AES) for use by educators and students. Additional resources from AES are available to the medical and scientific community. Visit www.aesnet.org to find more. The following is an example of proper attribution for this work: St. Louis, EK, Frey, LC (Eds.). Electroencephalography (EEG): An introductory text and atlas of normal and abnormal findings in adults, children and infants. Chicago, IL: American Epilepsy Society; 2016. http://dx.doi.org/10.5698/978-0-9979756-0-4. About the American Epilepsy Society The American Epilepsy Society is a medical and scientific society whose members are engaged in research and clinical care for people with epilepsy. For more than 75 years, AES has provided a dynamic global forum where professionals from academia, private practice, not-for-profit, government, and industry can learn, share, and grow. Find out more at www.aesnet.org. The Society seeks to promote interdisciplinary communications, scientific investigation, and exchange of clinical information about epilepsy. This publication was produced through the volunteer efforts of the AES Council on Education, Student & Resident Education & Curriculum Committee, and the EEG Work Group. Correspondence American Epilepsy Society 135 S. LaSalle St., Suite 2850, Chicago, IL 60603 Phone: (312) 883-3800 | email: [email protected] | website: www.aesnet.org Erik K. St. Louis, MD - Ex Officio Work Group Chair, Primary Author & Editor Departments of Neurology and Medicine, Mayo Clinic 200 First Street SW, Rochester, MN 55905 Phone: (507) 266-7456 | email: [email protected] Lauren Frey, MD - Workgroup Chair & Editor Department of Neurology, University of Colorado Phone: (720) 848-8583 | email: [email protected] 2  Electroencephalography Table of Contents Introduction Brief History and Background An Orderly Approach to EEG Analysis: Visual Inspection of the Background and Pattern Recognition....................................................................................... 6 Calibration Orientation and Nomenclature Clinical Approach The Normal EEG............................................................................................. 8 The Background Provocation Techniques Drowsiness and Sleep The Developmental EEG: Premature, Neonatal, Infant, and Children....................... 20 Neonatal EEG Infant and Pediatric Developmental Changes in the EEG Benign Variants in the EEG.............................................................................. 42 The Abnormal EEG........................................................................................ 48 Focal and Generalized Slowing and Significance Encephalopathies/Delirium Dementias Coma Anesthetic Patterns EEG in the Epilepsies...................................................................................... 56 Routine Interictal EEG in Epilepsy and Spells Ictal EEG Applications and Formats Nonepileptic Spells Epileptic Seizure Classification and Types Long-term Video-EEG Monitoring With Intracranial Electrodes Urgent and Emergent EEG for Evaluation and Treatment of Acute Seizures............... 73 References.................................................................................................... 80 Additional Texts and Recommended Readings.................................................... 81 Appendix 1. The Scientific Basis of EEG: Neurophysiology of EEG Generation in the Brain...................................................................................................... 81 Appendix 2. Principles of Digital EEG................................................................. 81 EEG Signal Collection and Display Advantages of Digital EEG Appendix 3. Principles of Electrical Safety.......................................................... 83 Appendix 4. Common Artifacts During EEG Recording.......................................... 84 Eye Movements Tongue Movements, Talking, and Chewing Movement Artifacts Electrode Artifacts Sweat Artifact Appendix 5. EEG Standards and Examples for the Determination of Brain Death....... 94 Appendix 6. A Brief History of EEG.................................................................... 95 3  Electroencephalography Introduction Brief History and Background The first known neurophysiologic recordings of animals were performed by Richard Caton in 1875. The advent of recording the electrical activity of human beings took another half century to occur. Hans Berger, a German psychiatrist, pioneered the EEG in humans in 1924. The EEG is an electrophysiological technique for the recording of electrical activity arising from the human brain. Given its exquisite temporal sensitivity, the main utility of EEG is in the evaluation of dynamic cerebral functioning. EEG is particu- larly useful for evaluating patients with suspected seizures, epilepsy, and unusual spells. With certain exceptions, practically all patients with epilepsy will demonstrate characteristic EEG alterations during an epileptic seizure (ictal, or during-seizure, record- ings). Most epilepsy patients also show characteristic interictal (or between-seizure) epileptiform discharges (IEDs) termed spike (70 Hz). The term “ripples” (generally >100 Hz) are thought to reflect epileptiform discharges (see Figure 6). Clinical Approach There are different opinions as to whether one should review the clinical history prior to EEG interpretation. Some experts prefer to know the patient history prior to interpreting the EEG, so that the likelihood of a potential abnormality can be interpreted within its appropriate clinical context. Others think that knowing the history biases the interpretation and may lead to “overcall- ing” or “undercalling” questionable findings. There is potential value in both approaches, and one solution is to first read through the tracing without the history of the patient, and then take a second pass after reviewing the history. The Normal EEG The Background One of the initial goals for EEG interpretation is determination of the background. To gain a complete sense about the background EEG, one should employ a variety of different screening montages to enable several different perspectives of its chief frequencies, amplitude, and degree of synchrony. Figure 6. Ripples from intracranial EEG recordings. (Figure courtesy of Greg Worrell, MD, and Ben Brinkmann, PhD, Mayo Systems Electrophysiology Laboratory, Mayo Clinic Rochester). 8  Electroencephalography Common Physiological Artifacts Artifacts are common during the wakeful EEG, and one of the first hurdles of EEG interpretation is distinguishing these from cerebral signal. Most notable is the presence of low-amplitude, high-frequency activity arising from scalp muscles, often frontally dominant but seen throughout the tracing. Rapid eye movements (REMs), resulting from saccades and spontane- ous changes of gaze, may be seen as small, rapid deflections in frontal regions. Extremely large-voltage, diphasic potentials in frontal regions result from blinks. This occurs because the eye is a dipole, relatively positive at the corneal surface and negative at the retinal surface, and the eye moves characteristically upward during a blink according to Bell phenomenon, resulting in a moving charge and potential change. Since the positivity of the cornea rotates upward toward frontal electrode sites, a transient positivity, then negativity is recorded there. Another common artifact during the waking EEG is caused by swallowing and the related movement of the tongue, which similar to the eye is a dipole and causes a slow potential with superimposed muscle artifact. See Appendix 4 for representative common EEG artifacts seen during wakefulness. The Posterior Dominant Rhythm Healthy adults typically manifest relatively low-amplitude, mixed-frequency background rhythms, also termed desynchro- nized. When the patient is relaxed with eyes closed, the background is usually characterized by the posteriorly dominant alpha rhythm, also known simply as the posterior dominant rhythm. (Figure 7). The alpha rhythm, or alpha, is attenuated in ampli- tude and frequency and often completely ablated by eye opening. Alpha amplitude is usually highly symmetrical, although it may be of somewhat higher amplitude over the right than left posterior head regions (greater than 50% amplitude asym- metry is considered abnormal, with the abnormality usually on the side of the lower amplitude). Alpha frequency normally remains symmetrical, so if one side is slower than the other, an abnormality of cerebral functioning exists on the slower side. The alpha generator is thought to be located within the occipital lobes. While some normal patients lack well-formed alpha activity, the frequency, symmetry, and reactivity of alpha merits special attention and comment in any EEG report. There are several variants of the alpha rhythm, and they include temporal alpha, characterized by independent alpha activity over the temporal regions seen in older patients, frontal alpha, consisting of alpha activity over the anterior head regions, which may Figure 7. The posterior dominant alpha rhythm. The normal background EEG during wakefulness contains posteriorly dominant, symmetrical, and reactive alpha rhythm. Alpha activity is more prominent in amplitude during relaxed, eyes-closed wakefulness and demonstrates reactivity by decreas- ing in amplitude and presence during eye opening and mental alerting. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Erik K. St. Louis, MD. 9 Electroencephalography be related to drugs, anesthesia, or fol- lowing arousal from sleep (Note: When invariant and unreactive to any stimuli in a comatose patient, this variant is pathologi- cal and represents an alpha coma pattern.) or paradoxical alpha, which is a return of alpha activity with an alerting stimulus or eye opening. Other Features of the Normal Waking Back- ground The remainder of the normal waking EEG is usually composed of lower amplitude beta frequencies in the fronto-centro-temporal head regions (see Figure 8). Beta frequen- cies are generally over 13 Hz and of low Figure 8. Excess beta activity. In example (a), generalized excess beta activity is shown in a modified alternating bipolar montage. In example (b), a very prominent frontally maximal beta rhythm is noted in this slightly drowsy 32-year-old woman, very likely as a result of recent lorazepam ingestion for anxiety. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. (a) Generalized excess beta. Figure courtesy of Jeffrey W. Britton, MD. (b) Frontally predominant excess beta activity. Figure courtesy of Jennifer L. Hopp, MD, University of Maryland.v 10  Electroencephalography amplitude. Beta is often enhanced during drowsi- ness, seen in a precentral distribution, and felt to be related to the functions of the sensorimotor cortex. When beta is prominent in amplitude, either in the frontal or generalized dis- tribution, it is likely a result of the use of sedating drugs such as benzodiazepines or barbiturates. In this sense, it is a mild abnormality of the background and often referred to as “excess beta” (Figure 8). Sometimes, a promi- nent alpha-range fre- quency of 8 to 12 Hz is seen over the central head regions, termed the mu rhythm (Figure 9). Mu is seen in between 20 and 40 percent of normal adults, is characterized by arch- shaped (arciform) waves occurring either unilater- ally or bilaterally over the central regions, and is prominent during drowsi- ness. Mu is unrelated to eye opening or closure and reacts to movement, so- matosensory stimulus, or the thought of movement. It is thought to be gener- ated in the rolandic region of the frontal and parietal lobes in relation to func- tions of the sensorimotor cortices. The technologist should instruct the patient to wiggle their thumb to distinguish mu from alpha; mu will attenuate, whereas alpha is unchanged, by movement or intention to Figure 9. Mu rhythms. (a) A prominent Mu rhythm is seen over the right central region. Note the arciform waves of move. approximate alpha-range frequency of 8 to 12 Hz. Mu is reactive to movement or the thought of movement, unlike alpha activity, which is reactive instead to eye opening. Longitudinal bipolar montage. (b) Trains of asynchronous mu are seen over either central region during drowsiness. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. (a) Right central mu activity. Figure courtesy of Jeffrey W. Britton, MD. (b) Asynchronous mu, bilateral central regions. Courtesy Dr. Jennifer L. Hopp, MD, University of Maryland. 11 Electroencephalography Slower Background Rhythms Occasional slower theta (4–7 Hz) or even delta (1–3 Hz) frequencies transiently may be seen during normal wakefulness, but usually these slower activities only become prominent during drowsiness (Figure 10). In children, adolescents, young adults, and some elderly individuals, it is frequent and entirely normal for there to be “drowsy bursts” of generalized theta–delta frequency activity on the EEG (Figure 10). Intermittent or pervasive, focal or generalized, theta or delta frequency, range slowing of the background in a vigilant adult is abnormal and indicates either focal, regional, or generalized cerebral dysfunction (see section on Abnormal Background for further discussion on the significance of background slowing and for example Figures). Figure 10. Background in drowsiness. Normal EEG during drowsiness in an 8-year-old child, illustrating background theta and delta frequency slowing and a “drowsy burst” of frontally dominant theta activity in the third and fourth seconds. Such findings are normal in this age group and should not be overinterpreted as a sign of encephalopathy or seizure disorder. Longitudinal bipolar montage. Copyright 2013. Mayo Foundation for Medical Educa- tion and Research. All rights reserved. Figure courtesy of Jeffrey W. Britton, MD. 12  Electroencephalography An additional normal background phenomenon is the occurrence of lambda waves (Figure 11). Lambda is elicited by pattern viewing, having the configuration of the Greek letter lambda (Λ) and is a surface positive, occipitally predominant waveform. Figure 11. Lambda waves. Lambda waves over posterior head regions, elicited by complex pattern viewing. Note the surface positive waveforms over both occipital regions. Longitudinal bipolar montage. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Jeffrey W. Britton, MD. 13  Electroencephalography Provocation Techniques During the wakeful EEG recording, provocative maneuvers are usually administered in an effort to produce possible background or epileptiform abnormalities, including hyperventilation and photic stimulation. In adults, hyperventilation often produces minimal change, but in children, adolescents, and young adults, a prominent high-amplitude or hypersynchronous background- slowing phenomena termed “buildup” is often seen and is considered a normal finding in these age groups. The expected normal findings during photic stimulation are either no change in the background, or a symmetrical “photic driving” response, consist- ing of entrainment of the background alpha rhythm to the same or a harmonic frequency variant of the administered flashing lights (see Figure 12, below). A similar finding is sometimes seen over the frontal head regions induced by photic stimulation, but this represents instead evoked responses from retinal neurons, the electroretinogram (ERG), which is distinguished by its purely anterior (rather than posteriorly predominant photic stimulation) response (see Figure 13, below). See the section on Abnormal Background for further discussion concerning typical abnormalities induced by activating procedures during EEG. Figure 12. Photic stimulation. Photic stimulation responses include either no change in the background or, as shown below, symmetrical entrainment of the background posterior rhythms over the occipital region. Longitudinal bipolar montage. Photic stimulus marked by gray ticks at bottom of figure. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Jeffrey W. Britton, MD. 14  Electroencephalography Figure 13. Photic stimulation may also induce an anteriorly dominant frequency in the EEG, but this emanates from evoked retinal neuronal responses, the ERG. The ERG artifact is caused by retinal depolarization induced by photic stimulus shown in FP1 and FP2 derivations on a longitudinal Laplacian montage. The ocular source of waveforms was established by covering the right eye, which blocked stimulation of the right retina eliminating ERG in the FP2 derivation. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Jeffrey W. Britton, MD. 15 Electroencephalography Drowsiness and Sleep During drowsiness, the first discernible change is gradual loss of the frequent muscle and movement artifacts and reduction of blinks and rapid lateral eye movements. Instead, a very slow frequency of 0.25 to 1.0 Hz in the frontal and lateral frontal channels emerges. These are slow rolling eye movements, or SEMS (slow eye movements of sleep), which begin in drowsiness and persist through stage 1 sleep, until gradually being lost with deeper stages of non-rapid eye movement (NREM) sleep. The EEG during drowsiness contains slower, synchronous frequencies of theta and delta throughout the background (see Figure 14). Defining features of sleep stages are listed in Table 1. NREM sleep is classified as light NREM (stages 1–2; now termed N1–2) and deeper slow wave sleep (SWS, formerly known as stages 3–4; N3–4), as well as REM sleep. Typically, approximately 75% of the night is spent in NREM sleep and up to 25% in REM sleep. Stage 1 (N1) sleep is contiguous with drowsiness and is characterized by SEMS and slower theta and delta EEG frequencies of 1 to 7 Hz, with less than 50% alpha frequency activity in a 30-second epoch. It is easily marked by the appearance of vertex waves (V-waves); sharply contoured, fronto-centrally predominant waves (Figure 15). Figure 14. Example of drowsiness from a normal adult EEG recording. Note the prominent theta and delta activity, lack of eye movements or blinks, lack of muscle or movement artifact, and early suggestion of slow lateral rolling eye movements best seen in the F7 and F8 containing derivations. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Erik K. St. Louis, MD 16  Electroencephalography TABLE 1. Defining Features of Sleep Stages on the EEG State Frequency, Hz Amplitude Feature(s) Other Awake 8–13 Low Desynchronized Blinks, swallowing, muscle Drowsiness 3–7 Mixed More synchronized, SEMS Blinks, muscle drop out Stage 1 (N1) 3–7 Mixed V-waves, SEMS Rare POSTS Stage 2 (N2) 1–7 Moderate Synchronized, K-complexes, spindles, Delta power higher POSTS SWS 1–5 High Delta >20% K-complexes, spindles, and POSTs recede REM 4–8 Low Desynchronized, REMs, sawtooth waves Figure 15. Stage 1 (N1) sleep. Characterized by slow rolling eye movement artifacts, and slower theta and some delta frequencies in the EEG back- ground. V-waves (V) also typically occur. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Erik K. St. Louis, MD. 17 Electroencephalography During stage 2 (N2) sleep, more delta frequency background begins to emerge, and the defining features of sleep spindles, K-complexes, and posterior occipital sharp transients of sleep (POSTS) are seen (Figures 16, 17). Sleep spindles are thought Figure 16. Stage 2 (N2) sleep. Slower theta and some delta (by definition, less than 20% of background of delta range slowing) frequencies in the EEG background. K-complexes and sleep spindles are the hallmarks of N2 architecture. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Erik K. St. Louis, MD. 18  Electroencephalography Figure 17. Slow wave sleep (N3) contains greater than 20% high-voltage (>75 µV crest to crest) delta frequencies and fewer K-complexes and spindles. The figure below was taken from a full EEG recording during a polysomnogram, since N3 sleep is typically not recorded during laboratory daytime re- cordings unless there has been substantial sleep deprivation preceding the study. Note the high-voltage delta activity in the first half of this 15-second epoch, followed by a spontaneous arousal. The event following is actually an NREM parasomnia (a confusional arousal) in which the patient sat up and stared around the room, appearing confused. The patient was later amnestic for the event. High-voltage delta activity can be seen persisting behind the muscle and movement artifact as the patient sits up, which is often seen in NREM arousal disorders. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Erik K. St. Louis, MD. 19  Electroencephalography to reflect the synchronous activity mediated by thalamo-cortical neuronal networks. SWS (N3) has similar features, but less spindles, K-complexes, and POSTS are seen and even more delta frequency activity emerges (Figure 18). REM sleep was previously known as paradoxical sleep, because REM actually resembles the waking EEG more closely than NREM sleep, having a desynchronized, low-voltage background. There are also fronto-central, sharply contoured theta frequen- cies called sawtooth waves, as well as REM artifacts seen in lateral frontal sites (Figure 18). Proper sleep-staging criteria also require features of very low-voltage chin electromyography (EMG) and eye movements recorded by electrooculogram (EOG) channels, but these polysomnographic channels are not routinely recorded during outpatient EEGs. The Developmental EEG: Premature, Neonatal, Infant, and Children Neonatal EEG The neonatal EEG has some very different clinical considerations for recording and interpretation. Understanding certain clinical details, such as the conceptional (aka conceptual) age (CA) and the clinical state of the recorded patient, is essential for interpreta- tion of the neonatal EEG. The indications for the conventional neonatal EEG include assessment of age and maturity; identification of neonatal seizures and neonatal status epilepticus; evaluation of neonatal encephalopathy and focal abnormalities; and assessment of response to treatment or to aid neurologic prognosis. The conventional neonatal EEG is the gold standard for the diagnosis and confirmation of neonatal seizures and neonatal encephalopathy. Figure 18. REM sleep is characterized by a more typically wake-appearing, desynchronized, mixed-frequency background, which may contain alpha frequencies, characteristic centrally dominant sharply contoured sawtooth waves, and rapid eye movement artifacts in lateral frontal electrode sites. Copyright 2013. Mayo Foundation for Medical Education and Research. All rights reserved. Figure courtesy of Erik K. St. Louis, MD. 20  Electroencephalography There are also several specific technical considerations for neonatal EEG, beginning with the montage and electrode place- ment. The neonatal montage is used from the time of birth until the baby reaches full-term age. In some centers, the neonatal montage is used until the baby is 46 to 48 weeks gestational age (GA) or until sleep spindles are seen in the recording (around 46–48 weeks) (see Figure 19). Figure 19. The 10-20 System electrode placements modified for neo- nates. Most of the neonatal EEG activity is found in the central regions of the brain, therefore the neonatal montage should have sufficient cover- age of the centro-temporal regions. Figure courtesy of Elia M. Pestana- Knight, MD, Cleveland Clinic Foundation. A study from Tekgul and colleagues compared the sensitivity and specificity of the reduced (neonatal) montage versus a full 10-20 montage in neonates (4). They found that the neonatal montage had a sensitivity of 96.8% and specificity of 100%. An elec- trode cap is used in some institutions in which there is no 24-hour EEG technologist coverage, since a cap can be placed by nurses, residents, or fellows. Electrocaps are color coded and can be adjusted to fit different head sizes. Other polygraphic parameters or extracerebral channels that are included in the conventional neonatal EEG are the electrooculogram (EOC), electromyogram (EMG), electrocardiogram (ECG), pneumograph, and video. For the EOC, two EOC electrodes are placed near the outer canthus of the eyes, one above the eye and the other below the eye. EOC allows for identification of different behavioral stages, in particular awake and active sleep stages, where eye movements are seen. For EMG recordings, the EMG electrode is placed under the chin. EMG allows for the identification of different behavioral stages (awake and active sleep), since active sleep is often associated with relative muscle atonia. ECG leads are located on the chest to record variations of the heart rate and allow distinction of ECG artifact on the EEG. A pneumograph or respiratory belt also allows for the identification of behavioral stages. Synchronized video recording should also be used when possible, although a well-trained EEG technician or nurse annotating the EEG record can help substitute for track- ing behaviors of the patient or environmental issues that may generate EEG artifacts, such as patting or nurse manipulation; this is crucial since sometimes movements such as these may generate artifacts that almost precisely mimic seizure patterns on the neonatal EEG. Newborns, in particular preterm babies, have very thin and sensitive skin. Even when the recommendation is to keep the skin impedance (a measure of the quality of the connection between the skin and the recording electrode) at around 5 kΩ, an impedance of approximately 10 kΩ also may produce a technically adequate recording, while avoiding severe skin abrasions. The low-frequency filter is set lower in neonatal recordings than for EEG recordings in older children and adults to allow for the record- ing of slower frequencies at 0.005 to 0.01 Hz or 0.5 Hz, and the high-frequency filter setting is similar to adult recordings at 35 to 70 Hz. Neonatal EEG recording should last at least 2 to 3 hours to capture awake and all sleep stages. Neonatal EEG is typically displayed with a longer time interval on the screen (a faster “paper speed” of 15 mm/s) producing a more compressed-appearing recording. This compressed screen allows for better display of very slow activity, asymmetries, and asynchronies that are crucial to evaluate in neonatal recordings. 21 Electroencephalography Neonatal montages have some variations between institutions. The main variations are where the different channels are located on recording montages and how they are displayed on the screen or page (see Figure 20 for a typical neonatal montage display). To provide an accurate interpretation of the neonatal EEG, it is important to know the conceptional age (aka conceptual age) (CA) of the baby, the medications the baby is taking at the time of the recording, the different behavioral states of the baby, and any pertinent environmental changes. The CA is calculated by adding the estimated GA and the legal or chronologic age of the patient following birth. An example is a 4-week-old baby born at 30 weeks GA would have a CA of 34 weeks. Taking into account the CA, a neonate is a newborn infant with age