Technical aspects of EEG …

Epilepsy & Seizures

Updated 06.24.2025
Released 01.11.2018
Expires For CME 06.24.2028

Technical aspects of EEG

Authors: William O Tatum IV DO FACNS, Dawn Radford DO, Anteneh M Feyissa MD MSc

See Contributor Disclosures

Editor: John M Stern MD

Cite this article

Technical aspects of EEG

In This Article

Quick Link

Introduction

Overview

Since the first EEG recordings by Hans Berger in the 1920s, the electroencephalogram (EEG) has remained a pivotal diagnostic tool analyzing the brain’s 3-dimensional electrophysiological activity in a 2-dimensional format for interpretation. EEG graphically displays voltage differences between two sites of the brain to represent intrinsic function recorded over time. Because surface electrodes are routinely used to record EEG, the scalp, skull, and meninges serve as barriers to influence the EEG; therefore, features of the cortical waveforms may be altered. To ensure the accuracy of the recording where very low amplitude electrophysiological potentials are encountered, the technical aspects of recording are important to understand and maintain.

Interpreting EEG necessitates a baseline understanding of electrophysiology, biological aspects of recording, and physical principles to achieve accurate pattern recognition. Adherence to the 10 to 20 international system of electrode placement, principles underlying instrumentation and electrical safety, standardized digital recording, and applying crucial recording concepts throughout the performance of the EEG are a few important technical requirements and incorporate advances in technology over time. However, the technical challenge of recording interpretable EEG with little or no artifact has remained the same, though artifact reduction and elimination algorithms have helped limit “interference” with interpretation. Importantly, EEG must be run by an experienced and knowledgeable technologist capable of supervising the technical aspects of the recording, from electrode application to visual display for interpretation by a physician, as well as storing and archiving the data. In this article, the authors discuss important technical aspects of EEG that may influence the recording quality and, as a result, impact the clinical application of scalp EEG.

Key points

	• The EEG procedure begins with electrode placement using the international 10-20 system. Instrumentation includes all components that connect the patient to the EEG machine. With each component of a recording system, there is potential to encounter interference or noise from outside sources that produce artifactual signals capable of obscuring brain-generated waveforms.
	• The electrodes are a part of the recording system that are connected by leads to the EEG machine. Electrodes are the weakest link in ensuring the integrity of the EEG recording due to technical limitations predisposing to artifact. Silver-silver chloride and gold electrodes are applied after debridement of the skin surface using an adhesive paste as an electrical conduit (30). Interelectrode impedances up to 10 kilo-ohms (kOhms) are acceptable, but optimal recording still requires balanced impedances (18). New electrode technologies, including dry electrodes that do not require gel, electrode caps, and rapid EEG devices to reduce the delay in obtaining an EEG in acute neurologic settings, eliminate the need for trained EEG technologists to secure individual electrodes and save timely delays in recording (23).
	• The pins on the tip of the electrodes connect the electrode lead wires to the jack box. Electrode leads have a site-specific location on the jack box, reflecting the anatomical location where the electrode is attached to the head. The jack box is connected via an insulated input cable to the EEG machine, where amplification of the waveforms occurs. The EEG machine can arrange waveforms for visual display in a montage. The electrodes are compared by the differential amplifier to be arranged as pairs (bipolar) or as single (monopolar or referential) measurements. The montage then configures them in a “map,” which typically displays them for visual analysis using a left-over-right array for visual analysis (01).
	• Amplifiers are designed to increase the sensitivity of waveform detections recorded from the brain and filter the frequencies recorded. The EEG machine has a low-frequency filter (high pass), a high-frequency filter (low pass), and a 60-Hz notch filter. Standard settings of 7 µV/mm sensitivity, 70 Hz high-frequency filter, and 0.5 Hz or 1 Hz low-frequency filter should be the initial parameters of recording EEG.
	• Sampling rates are based on the Nyquist-Shannon theorem. The minimum sampling rate should be at least 256 samples per second; however, 512 hertz (Hz) is preferred to prevent “aliasing” high frequencies that may be falsely displayed as lower frequencies using high-resolution computer screens (05).
	• The risks associated with performing an EEG are very low, but the potential for adverse electrical safety exists if the ground is faulty or if there is more than one ground used. In this case, electricity could inadvertently be conducted through the patient and produce bodily harm. In addition, fire hazards represent a rare electrical concern if high oxygen levels are in use while operating the EEG machinery. Rarely, cutaneous infections, metal allergy, or focal inflammatory responses may result from electrode contact with the scalp.

Historical note and terminology

The first known tracing in animals of fluctuating cortical potentials that constitute the EEG was performed by Richard Caton. He was a physician and physiologist from Liverpool, England, who in 1875 used a galvanometer to discover the electrical nature of the brain in rabbits and monkeys (33). In 1924, a German neuropsychiatrist, Hans Berger, performed the first EEG recording in humans using a Siemens double-coil galvanometer and published his first report of a human 3-minute EEG recording in 1929 recognizing the alpha rhythm. Berger could not observe the recording live; instead, he had to develop the paper form of EEG, similar to a photograph to visualize the recording (06). Berger continued to advance in his attempts to record EEGs as technology improved. His colleagues at the Institute of Brain Research in Berlin made significant improvements in the quality of the EEG with the help of JF Tonnies, who was an engineer at the institute. From the initial 1-channel EEG, Tonnies is credited with developing the first ink-writing oscillograph, which he called the neurograph. He went on to develop the first differential amplifier as well as the concepts of impedance and volume conduction (33). In the late 1920s, electrical engineer Harry Nyquist determined that the number of independent pulses that could be put through a telegraph transmitting the number of channels over a unit of time was limited when it was less than twice the bandwidth of the channel (05). In the 1940s, Claude Shannon expanded on the Nyquist theorem to incorporate the sampling rate that became known as the Nyquist-Shannon theorem. Current sampling rates in digital equipment are based on the Nyquist-Shannon sampling theorem to prevent “aliasing” of the EEG data and false representation of the brain signal caused by a lower sampling frequency than the actual waveform. Nearly all proprietary EEG systems now provide 512 Hz sampling rates to ensure adequate representation of the wide range of frequencies in the EEG.

By the 1950s, EEG technology started to become invasive, and the use of invasive electrodes and the exploration of deep intracerebral regions began. In the 1980s, data collection and analysis developments allowed the EEG to be digitalized and recorded on videotape. The first-generation commercial digital EEG systems were introduced in the 1990s (33). Over the years, computerized networking enabled remote EEG reading and simultaneous video recording of the patients, making continuous EEG (cEEG) a reality (25; 22). As manual review and interpretation of cEEG became increasingly labor-intensive, methods were developed to assist in rapid and accurate EEG interpretation. In the last 2 decades, complex algorithms enabling quantitative EEG analyses, such as wavelet analysis and Fourier analysis, were developed to improve the display of the EEG signal (10). Automated spectral analysis was introduced to study spectral arrays using the Fast Fourier Transform to generate a spectrogram, a color plot providing the temporal dispersion of the EEG frequency spectrum separated by the power contained in independent components for analysis (22). These methods have improved the ease and diagnostic power of EEG by displaying quantitative frequency representation in trends, especially in intensive care units (29).

Terminologies. Understanding the technical aspects of recording EEG requires a foundation of terminology encompassing its instrumentation. The following is a glossary of terms that are used to facilitate the concepts involved in recording EEG.

Aliasing. Aliasing is a signal-processing term. Aliasing occurs when a system is measured at an insufficient sampling rate and creates a frequency misrepresentation of the recorded activity.

Amplifier. An amplifier is an electronic device that can increase the power of a signal. An amplifier functions by using electric power from a power source to increase the amplitude of the voltage or current signal. The amplifier gain is the ratio of the output signal to the input signal.

Analog to digital converter (AD converter). Analog to digital converter is a system that converts an analog signal into a digital signal.

Artifacts. Artifacts are noncerebral signals that often contaminate the recordings in both temporal and spectral domains within a wide frequency band. Internal sources of artifacts may be due to physiological activities of the subject (eg, ECG, EMG or muscle artifacts, EOG) and its movement. External sources of artifacts are environmental interferences, recording equipment, electrode pop, and cable movement. In addition, some artifacts appear focal, whereas others appear diffusely.

Bandwidth. Bandwidth refers to a frequency range.

Bipolar recordings. Bipolar recordings are carried out where active electrode pairs are compared to record the difference between each pair.

Calibration. Calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. A mechanical calibration is performed at the beginning and end of each recording to test the accuracy of the amplifiers.

Capacitance. Capacitance is the ability to store an electrical charge.

Channel. Channel refers to the output of an amplifier that displays electrical information.

Common-mode rejection. Common-mode rejection refers to the characteristic of differential amplification where a signal that is the same in the two amplifier inputs is “rejected” or not recorded (there is no potential difference). Common-mode rejection ratio relates to the ratio of signal to noise.

Chart drive. Chart drive refers to the motion component of the EEG.

Derivation. Derivation refers to recording from an electrode pair with the output displayed in one recording channel.

Electrode. Electrode is a solid electric conductor through which an electric current enters or exits an electrolytic cell or other medium. The electrode is considered to be the first component in a series of instruments involved in recording EEG.

Electrode test. Electrode test is the test applied to electrodes to assess impedance.

Epileptiform discharges. Epileptiform discharges are the EEG patterns of spikes and sharp waves associated with an increased risk for developing seizures and epilepsy.

Filter. Filter refers to particular circuits within the amplifiers that attenuate frequencies or frequency bands.

Gain. Gain is the ratio of the output signal to the input signal, or the amount of magnification being used to amplify or increase the voltage of a signal.

Galvanometer. A galvanometer is an electromechanical instrument for detecting and measuring electric current.

High-frequency filter. High-frequency filters reduce the sensitivity of the EEG to high frequencies. It can be adjusted by a stepped control available on all EEG machines that perform digital recording.

Impedance. Impedance is the measurement of resistance to an alternating electrical current. To obtain a record with minimal electrical noise, the impedance of the scalp electrodes should be under 10 kOhms.

Input I. Input refers to the first of two electrode inputs measured by the EEG differential amplifier.

Input II. Input II refers to the second of two electrode inputs measured by the EEG differential amplifier.

Interictal. Interictal refers to the period between seizures, or convulsions characteristic of an epilepsy disorder.

Low-frequency filter. A low-frequency filter reduces the sensitivity of the EEG to record frequencies that are lower than the cut-off filter setting.

Jack box. A jack box is the electrode board receiving each pin of the electrodes. Electrodes are plugged into the jack box to pre-amplify and convert an analog signal to a digital format. Each site is labeled with the electrode’s anatomical name and is also configured as a head diagram to alleviate confusion about where to plug in the electrodes.

Nyquist-Shannon theorem. The Nyquist-Shannon theorem states that the sampling rate must be at least twice the highest analog frequency component.

Ground. Ground is the reference point in an electrical circuit from which voltages are measured.

Montage. The montage is a standardized arrangement of selected pairs of electrode channels displayed in a “map” of the brain’s electrical activity chains for review. The most common montage is the A-P (anterior-posterior) longitudinal bipolar montage (aka the “double banana”). This is because the electrode configuration has the appearance of two bananas laid front to back over each of the brain hemispheres when the electrodes are connected. In a bipolar montage, neighboring electrodes may be paired in a chain to form an array either anterior to posterior (longitudinal bipolar) or side to side (transverse bipolar). The ACNS recommends that a standard EEG recording should contain at least one longitudinal bipolar montage, one transverse bipolar montage, and one referential montage.

Notch filter. A notch filter is a circuit that filters out narrow band frequencies, for example, a 60 Hz (or 50 Hz) signal. This is particularly important when recording in intensive care unit settings where various electrical equipment is used.

Oscillograph. An oscillograph is a device that records the waveforms of changing currents, voltages, or any other quantity that can be translated into electric energy, such as sound waves.

Phase reversal. Phase reversal refers to the principle means of electrophysiological localization using bipolar recording. The phase reversal reflects the maximal amplitude electrophysiological phenomenon of interest (eg, spikes or sharp waves) where waveforms “point” towards each other in adjacent channels “reversing” their deflection in the up and down directions.

Polarity. Polarity refers to negative, positive, or neutral values and relates to the polarity convention, which dictates that an upward deflection is surface-negative and a downward deflection is surface-positive.

Reactivity. Reactivity refers to an alteration of EEG activity by external sensory stimuli.

Reference electrode. Reference electrode refers to an electrode that is electrically inactive relative to the active electrode site. This reference electrode remains consistent compared to electrodes in the montage. Examples of a reference electrode include ipsilateral ear/mastoid or the vertex location comparing a single electrode to all others in the electrode array. In a referential recording, the activity from the active electrode is compared to the reference to produce a potential difference where absolute amplitude remains the site of maximal electrophysiological involvement.

Resistance. Resistance is opposition to direct electrical current (DC) flow.

Sensitivity. Sensitivity refers to the ratio of input voltage to output recorded in a channel of the EEG recording.

Clinical aspects

Description

EEG studies are conducted either as routine (short duration) or continuous inpatient and outpatient ambulatory studies. Although routine EEG can help establish the diagnosis of epilepsy, continuous outpatient ambulatory EEG and inpatient long-term video-EEG monitoring have an important role in the assessment of patients who present diagnostic or management difficulties following clinical evaluation and a routine EEG (42; 37). The initial step in performing EEG involves measuring and marking the patient’s head; this is a vital first step that needs to be taken by the technologist. After adequate scalp preparation, electrodes should be placed according to the international 10-20 system. The ACNS recommends using a minimum of 21 electrodes for recording EEG for clinical purposes (30). Each electrode site is designated by a letter and a numerical value. Letters represent which lobe of the brain the electrode position overlies (eg, F = frontal, T = temporal, P = parietal, and O = occipital). Odd-numbered electrode sites appear on the left side of the head; even-numbered electrodes are on the right side; “z”-labeled sites are in the sagittal midline from anterior to posterior; and “A” or auricular sites are on the mastoid processes or ears. New electrode technologies, including dry electrode cap models that don’t require gel, are being tested to reduce the delay for obtaining an EEG in acute neurologic settings and eliminate the need for trained EEG technologists to place the electrodes (23). In addition to the scalp electrodes, the EEG can monitor other parameters, such as eye movements, heart rate, respiration, and muscle activity (polygraphic recording), to enhance the recording when needed (28).

Calibration is an integral part of every EEG recording. It gives a scaling factor for the interpreter and tests the EEG machine for sensitivity, high-frequency and low-frequency response, noise level, and pen alignment and damping (for analog systems). At the outset, if necessary, all channels should be adjusted to respond equally and correctly to the calibration signal. Standard calibration includes at least 10 seconds (or the duration needed to reach a stable recording) of a square wave calibration. The calibration is performed with the standard settings and a known input of 50 µV. When doubt as to the correct functioning of any amplifier exists, a repeat calibration should be performed. Calibration voltages must be appropriate for the sensitivities used during the recording. A biological calibration reflects the recording of the most anterior electrode, which is usually Fp1, to the most posterior electrode, which is O2 is no longer required in digital recordings but can be useful in troubleshooting mechanical calibrations. After calibration, a visual review of a 30-second run on the system reference montage without the notch filter is also recommended (30).

The subject’s behavior and occurrence of artifacts should be the object of constant and vigilant attention during the entire recording, and the team should react appropriately when a problem arises (eg, artifact correction, clinical examination in case of seizures). Thus, the presence of an experienced technologist with experience in neurophysiology is highly recommended during the entire EEG recording. The minimal duration of a standard EEG is 20 to 30 minutes. It should include at least 3-minute hyperventilation and intermittent photic stimulation unless contraindicated. The technologist must update (annotate) these stimulations during the EEG test.

The use of standard equipment provided by most vendors allows for 64- to 256-input amplifiers, though these may not suffice for higher-density recording. Electrodes placed in accordance with the 10-20 international electrode placement system may serve to limit the identification of regions that may be enhanced by the use of a 10-10 system. The benefits of many of the proprietary systems are that most equipment will interface within the EEG laboratory, most include clinical applications involving software (eg, spike and seizure detection) and hardware (eg, push-button activation, video etc.), and most are capable of remote access. Furthermore, most EEG technologists will be familiar with digital EEG instrumentation and equipment beyond routine information technology or network support services and will not require extensive training on the performance and upkeep of standard equipment.

Ambulatory EEG (AEEG) is a technique that allows for portable testing that can be performed at the patient’s home. It is more easily accessible and cost-effective compared to inpatient video-EEG monitoring. AEEG can be done with or without video and is typically performed for several days in the patient’s natural environment (13). The American Clinical Neurophysiology Society published a guideline on the minimal technical requirements for performing AEEG in 2022. In general, AEEG setup may occur in the inpatient setting, outpatient clinic, or the patient’s home. It is recommended to have at least 25 electrodes (including 19 recording electrodes, a reference, a ground, two anterior temporal electrodes, and two ECG channels) using the International 10 to 20 system of electrode placement, as well as an event recorder. The use of a video camera is an optional feature; however, if it is included, it should consist of high-quality video cameras synchronized with the EEG recording. The patient and caregiver should be instructed to keep a written diary of the times and descriptions of push button events daily. It is recommended that all EEG data be available for review by the interpreter, and technical requirements for AEEG review are similar to those for routine EEG (37).

Scalp electrodes may be inadequate if seizures are infrequent as they are only acceptable to wear for up to 1 to 2 weeks. In comparison, sub-scalp ultra-long EEG monitoring allows for prolonged monitoring for months or even years. Multiple sub-scalp EEG devices have been developed that differ in electrode coverage, degree of invasiveness, and primary purpose. Subcutaneous electrodes are implanted between the scalp and the skull. Benefits of the sub-scalp approach include attenuation of various EEG artifacts and avoidance of external electrode maintenance. The devices are composed of leads with a range of sizes and contact numbers. Some devices require minimal sedation and are composed of a couple of electrodes, whereas others require general anesthesia with full head coverage (07). The recording electrodes are tunneled subcutaneously under the scalp and are attached to a recorder. The electrodes are connected to an external unit for power, data storage, and transmission. An external battery is required, and the device should be connected to a secure, cloud-based database where it can be reviewed by clinical staff (16). Cloud-based platforms are capable of storing large amounts of EEG data, allowing for retrieval and modification of previously saved EEG recordings (38).

Instrumentation for the clinical application of EEG (schematic)

(Contributed by Dr. William Tatum.)

Indications

An EEG is a foundational test in the differential diagnosis of epilepsy to distinguish seizures from other disorders associated with intermittent paroxysmal disturbances that resemble epileptic seizures (31; 04; 42). EEG can help support a clinical diagnosis of epilepsy when it demonstrates interictal epileptiform discharges. The presence of interictal epileptiform discharges in the EEG can provide an objective means of supporting the clinical diagnosis of epilepsy when the history is unclear in delineating a seizure (10). In addition, an EEG in patients with known seizures can serve to classify whether the seizures are focal or generalized and part of a specific epilepsy syndrome (11). Although the presence of interictal epileptiform discharges is highly specific for people with epilepsy, the sensitivity of EEG is only moderate, with 10% to 15% of individuals having repeatedly normal EEGs despite having been diagnosed with epilepsy (36). Nevertheless, the repeated absence of interictal epileptiform discharges may lead to questions of alternative diagnoses that may be unmasked when ictal recordings obtained through video-EEG monitoring are undertaken. In this manner, video-EEG monitoring may help differentiate those patients with nonepileptic behavioral events from epileptic seizures to obtain a definitive diagnosis. Similarly, video-EEG monitoring may help quantify seizures and spikes and identify patients for epilepsy surgery by characterizing the site of seizure onset as part of a comprehensive presurgical evaluation.

Scalp EEG may also help sort out different neurologic conditions that may present as altered mental status (34). For example, an EEG may suggest diffuse brain dysfunction or encephalopathy (eg, metabolic or toxic etiologies) or focal or multifocal dysfunction (eg, multiple strokes). Some specific conditions have characteristic EEG patterns, including herpes encephalitis, subacute sclerosing panencephalitis, or Creutzfeldt-Jakob disease. In addition, nonconvulsive status epilepticus, a prolonged seizure without overt clinical manifestations, may present only as altered mental status and may only be diagnosed with EEG. Continuous EEG may help demonstrate subclinical seizures in nearly 20% of critically ill patients admitted to the intensive care unit and is crucial in managing patients with status epilepticus. EEG is also useful in predicting the prognosis of comatose patients (34). The presence of a response in the EEG to activation procedures, such as somatosensory stimulation, is favorable compared with those that are unreactive in the appropriate clinical context. In addition, confirmation of neocortical death can be documented by at least 30 minutes of electrocerebral inactivity. Any brain-wave activity above 2 microvolts per millimeter precludes a diagnosis of brain death, and recommendations for a repeat study merit consideration. In the operating theater, scalp EEG monitoring has been useful to portend impending ischemic complications during endarterectomy. Ipsilateral loss of fast frequencies or hemispheric slowing on intraoperative EEG during carotid clamping may be averted by temporary shunt placement to maintain adequate cerebral blood circulation (43). Electrocorticography records EEG directly from the brain and may provide insight to tailor a resection in patients with epilepsy or brain tumors (12).

Contraindications

There are essentially no contraindications or risks associated with the proper use of EEG because it is a noninvasive procedure. However, an EEG should not be performed if the patient requires a high concentration oxygen as the electrical currents from the EEG machine can ignite the oxygen, resulting in an explosion. Patients with indwelling catheters are also at risk of electrical shock because they can provide a direct path to the heart for the passage of current.

Results

Reviewing EEG for interpretation is typically conducted at the hospital or the clinic where the EEG laboratory is located. Minimum technical standards are similar for routine (30) and continuous EEG as well as for EEG use in a hospital or outpatient setting (40). However, advances in computer science and internet technology with faster broadband connections and networking have enabled remote access to EEG. In addition, advances in digital EEG have allowed the electroencephalographer to reformat the record post hoc for greater flexibility during interpretation.

Following an assessment of the technical parameters of recording, the initial goal in the visual analysis of the EEG is a determination of the background. In the normal awake adult with eyes closed, an 8.5 to 12 Hz alpha rhythm appears maximal in the posterior part of the head, referred to as the posterior-dominant rhythm. The interpretation should consider the conditions of examination (eg, number of electrodes and patient’s alertness), clinical data, patient treatment at the time of the recording, and reason for the treatment (suspected pathology and types of electrical abnormalities). Abnormal EEG findings include those features that are nonepileptiform, interictal epileptiform discharges, and electrographic seizures. Nonepileptiform EEG abnormalities may be characterized by several distinct patterns, including focal slow activity, regional or generalized bisynchronous slow activity, generalized asynchronous slow activity, and focal or generalized suppression of the background activity. These patterns provide valuable information in investigating patients with epilepsy and patients with signs of acute brain insults, toxic-metabolic encephalopathy, neurodegenerative conditions, coma, and brain death (10). Interictal epileptiform discharges are characterized by the presence of spikes and sharp waves, with or without after-going slow waves, and are strongly associated with epilepsy. However, in rare cases, these discharges may also be seen in healthy subjects without seizures (32). Identifying focal or generalized interictal epileptiform discharges on EEG can support the clinical diagnosis of an epilepsy syndrome and help guide the management using antiseizure medication. Specific types of focal interictal epileptiform discharges are associated with specific types of epilepsy syndromes that are localization-related (eg, temporal lobe epilepsy) and may provide information about treatment options (eg, surgery) when co-localized to other areas of abnormal neuroimaging. Continuous outpatient ambulatory and inpatient long-term video-EEG monitoring in an epilepsy monitoring unit have a substantially greater yield than standard EEG recordings for the detection of seizures and epileptiform activity (09; 41). The absence of interictal epileptiform discharges may also provide useful information when epilepsy is in doubt though a normal EEG does not exclude the possibility of epilepsy.

Adverse effects

EEG is a safe and relatively easy procedure without a major risk; however, hospital patients are at higher risk of electrocution due to all of the many devices that are being used simultaneously. Low-resistance routes to the body are created with electrodes and intravenous lines that are connected to the patient as well as potential spillage of the intravenous fluids in proximity to the electrical outlets (08). Added precautions such as proper grounding of the electrical main should be adhered to in the intensive care setting. For safety reasons, EEG amplifiers are required to be isolated from earth ground; however, computer data acquisition system cases are typically connected directly to earth ground. Therefore, the EEG amplifier system, including instrumentation amplifiers and power supplies, is grounded to an "isolated common" voltage plane and chassis, which is at a floating potential with respect to earth. The maximum allowable current leakage on an electrode with ground connection is 10 µA. This requires a current limit on every lead or electrical isolation. A ground-fault interrupter should be in use in the power line to the operating room as well as other locations of the hospital (08). Even with the substantial improvements that have occurred in electrical safety, multiple patient grounds should be avoided to reduce the risk of electrical shock.

Neuroimaging safety is another issue where heating or burning may occur as radiofrequency or gradient fields during imaging produce current flow in electrode wires through induction. The use of Teflon or conductive plastic electrodes (using silver epoxy) is optimal though pure metals including silver (99.9%), gold, and copper also limit the potential for magnetization. Short lead wires may overcome coiling, which can induce electrical currents or become tangled on the MRI or CT equipment. Most connectors, however, are not MRI-compatible.

Special considerations

There are similarities between recording techniques, strategies of recordings, and interpretations of EEG features performed for both pediatric patients and adults. However, there are some differences in the different types of recording techniques and monitoring patients in different age groups (40; 41). For example, neonatal EEGs are typically performed utilizing a reduced number of electrodes per montage with lower gain compared to adults. In addition, noncephalic DC channels (polygraphy) for respiratory monitoring and pulse oximetry are often used in pediatric patients. Neonates also have thinner skin, and special care needs to be undertaken when applying the electrodes (17). Neonates are subject to a greater amount of artifacts in the EEG because they are usually in an incubator that controls oxygen and temperature regulation, which can negatively impact the technical quality. Similarly, EEGs obtained in special care units are challenging to record without artifacts due to interference by multiple electrical motorized devices (39).

In situations where EEG acquisition is difficult (eg, patients in the intensive care unit, agitated and delirious patients), electrodes with rapid application including nickel titanium, stainless steel, or silver wire electrodes may be considered (21). EEG caps or templates are becoming popular for rapid use in special care units to reduce the time and amount of technical support required (19) and rapidly determine if seizure emergencies are present (20).

Clinical vignette

An 18-year-old female with migraines was a cheerleader for her high school football team. She had just come from practice when she experienced an initial event that was felt to represent a seizure, and she was treated for epilepsy with antiseizure medication. While going to the water fountain prior to returning home from school, she was witnessed by her peers to “pass out” and was reported to have “seizure activity” with a loss of bladder control. She recovered and was sent to the local emergency department for evaluation. There, she was seen and diagnosed with syncope and released; she was told to follow up with her primary care physician. She was evaluated with both general and cardiovascular examinations that were normal. She was referred to a neurologist. A brain MRI was normal. An EEG performed in the office was reported to be abnormal due to generalized spike-and-slow waves. She was diagnosed with epilepsy and placed on valproate.

She presented with concern regarding the chronic administration of antiseizure medication with complaints of weight gain and hair loss. A history review disclosed recurrent dizzy spells since she was 16 years of age. She reported that the event occurred after skipping lunch the day of her “black-out.” She recalled becoming dizzy and nauseous and experiencing visual blurring; she then collapsed with a loss of consciousness. Her best friend reported a few jerks when she was down on the ground. Recovery was immediate without chest pain, palpitations, or racing of the heart rhythm. She had no risk factors for epilepsy. The general and neurologic examinations were normal. The EEG was repeated and compared with the “abnormal” one, which had similar features.

Case conclusions. A review of the “abnormal” EEG and an interpretation of the follow-up interictal EEG was performed.

EEG demonstrating hyogenic and eye flutter artifact

EEG sample demonstrating a 1-second burst of 4.5 Hz pseudo-generalized spike-and-waves (red arrows) due to superimposition of myogenic and eye flutter artifact. Note the out-of-phase deflection in the eye movement monitors (oval)....

The findings demonstrate a 1-second burst of 4.5 Hz pseudo-generalized spike-and-waves (red arrows) due to the superimposition of artifacts. Using an anterior-posterior longitudinal bipolar montage, in the frontal head regions eye flutter (validated by the eye movement monitors with an “out-of-phase” polarity) coinciding with myogenic spikes derived from the frontalis musculature was detected to create the false artifactual appearance of spike-and-waves. Photic stimulation was the trigger that produced the myogenic spikes that were time-locked to the frequency of the photic flash.

Case discussion. This case illustrates several important points to underscore the importance of appreciating the technical aspects of EEG recording. First, it illustrates the importance of the EEG in the misdiagnosis of epilepsy. Next, it reveals the pitfalls that may lead to misinterpretation from artifact (and, in this case, a combination of artifacts) as a common trap that may beguile even the most experienced electroencephalographer. Lastly, it underscores the importance of the technical application of eye movement monitors to validate the “slow waves” in revealing the eye as the generator. Placing an electrode above and below an extracerebral generator, such as the eye, allows for dipolar localization (the cornea is relatively electropositive relative to the retina). An “out-of-phase” deflection identifies the eye as the source of generating the waveforms. This is opposed to “in-phase” electrodes that commonly signal the brain as the generator. In addition, the frequency of a “spike” that is shorter than 15 msec is unlikely to be generated by the brain and instead more likely to be derived from a muscular source. When sustained, this may be recognized as a normal feature of the EEG known as the photomyogenic response.

This patient was “undiagnosed” with epilepsy and instead diagnosed with neurocardiogenic syncope after cardiology evaluation. A series of jerks in healthy individuals is a normal physiological response and when notable is referred to as convulsive syncope. She was tapered off valproate and given instructions for syncope prevention. Furthermore, the use of valproate as an antiseizure medication has been associated with a high risk of teratogenesis when exposure has taken place during the first trimester of pregnancy and can lead to birth defects in an unborn baby. Because many pregnancies are unplanned, obtaining the correct diagnosis involving seizure treatment (or migraine) needs to encompass gender-specific consequences that could occur from treatment. Fortunately, syncope did not recur with conservative treatment, and she has been event-free off antiseizure medication.

Scientific basis

Source generators. The biological signals represented by EEG are represented by the current movement of electrical charge (measured in coulombs) that flows within the nervous system. Charges are either positive or negative depending on the direction electrons are flowing. Separation of charge (polarization) is associated with the inherent ability of biological tissue. Current flows through electrical conductors (measured in amperes) such as the brain and also produces magnetic fields. Current (I) flow is equal to the change in charge (Q) over change in time (t) within a circuit where: I = dQ/dt.

The amount of potential energy (measured in joules) between 2 points determines the voltage. Electronic circuits in devices such as an EEG machine are designed to accommodate rapidly switching current flow in a bidirectional fashion (alternating current) as opposed to flow in only one direction (direct current). As current flows through the brain tissues, it experiences what is known as impedance (Z), which inhibits the flow of electrons. The flow of electrical current is proportional to voltage (V) and inversely related to resistance (R): I = V/R. Resistance does not account for capacitor and inductor impedances, whereas impedance is the sum of the circuit's resistance and reactance. Reactance represents the impedance from the electrical and electromagnetic fields generated from capacitors and inductors. Capacitors store energy in electrical fields, and inductors store energy in electromagnetic fields. The basic analog component of the EEG recording system is a circuit predicated on resistors and capacitors (RC circuit). The flow of electrical current in the circuit varies over time when a change in voltage occurs.

Traditional EEG displays electrophysiological fields on the scalp’s surface that vary in amplitude, frequency, and morphology and are related to both local cortical and distant subcortical generators (26). Scalp-recorded EEG oscillations are thought to be primarily generated by the summation of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) by cortical pyramidal neurons in the cerebral cortex (layers 3, 5, and 6) that are oriented perpendicularly to the brain’s surface. The diameter of an EEG electrode (10 mm) is several orders of magnitude larger than the size of single neurons (20 µm). Therefore, it requires pooled synchronous electrical activity derived from a source area of approximately 10⁸ neurons in a cortical area of a minimum of 10 cm² for most EEG signals to be detected at the scalp (27; 35). The brain waves are captured in microvolts, and the amplifier is designed to magnify the signal to see the signal by multiplying an input voltage by a constant range.

Electrodes and conductive media. Electrodes provide a critical first step in recording from biological tissues, such as the brain, to interface with metallic recording electrodes as part of an EEG system. Most electrodes are composed of silver-silver chloride sensors (nonpolarizing electrodes) and are good for recording high frequencies and DC potentials. These are produced by a thin layer of silver coating surrounding plastic substrates with an outer layer of silver converted to silver chloride. The silver-silver chloride use principle lies in converting oxidized silver cationic currents at the scalp’s surface to electron current that traverses the lead wire to reach the instrument for processing. Gel or paste, therefore, contains anions (free chloride) and serves as a conductive media. With chloride (anion) ions move to the electrode to bond with the silver; free electrons are then released and delivered to the lead wire to transmit the electrophysiological charge for amplification. An undesirable half-cell potential is created when there is an ionic charge imbalance between the electrolyte gel and the metal electrode. Silver-silver chloride electrodes have a low half-cell potential and lower resistance to charge flow. The Nernst equation is an important concept in evaluating the relative degree of reduction potential from various electrochemical properties of metals. New neuroimaging-compatible electrodes are available and composed of disposable plastic material (21). High impedance and unbalanced inter-electrode impedance have been proven to compromise the integrity of the EEG and allow noncephalic slower frequencies to be recorded (18). This is particularly challenging in the intensive care unit setting due to the abundance of other equipment that emits electrical noise (02). Current flowing through a conductor between two points is directly proportional to the voltage. Impedance to current flow within brain tissue causes a reduction. Paired electrodes through modern equipment can usually tolerate higher impedances identified at the scalp-electrode interface. Most electrodes should have an output impedance of 5 kOhms or less. To have a measurable and acceptable voltage, input impedances should have a minimum of 100 mOhms given Ohms Law equation (voltage = current x resistance).

A/D converter and grounding. Analog-to-digital conversion (jack box) converts a continuous analog signal in the EEG into a digital numerical series.

Instrumentation for the clinical application of EEG (schematic)

(Contributed by Dr. William Tatum.)

Time and amplitude in “steps” (expressed as bits) allow EEG to be quantified. Step size depends on the bit-value (expressed in a binary system of 1 or 0) of the computer and the maximal and minimal value of the steps that are possible by the amplifier to be transformed. The smaller the step size (usually 0.5 to 1 microvolt in most systems), the more accurate the digitization seen. New recommendations require a minimum of 16-bit conversion with a minimum amplitude resolution of 0.5 microvolts and dynamic range of +/- 1.638 millivolts with a minimum sampling rate of 256 samples per second and an anti-aliasing filter cutoff at two thirds the Nyquist frequency (14). Discrete time intervals sample a continuous waveform to express the samples as an integer. This 2-dimensional representation of time versus voltage has a sampling rate that determines how accurately the signal will be reproduced. The sampling rate is the rate at which the analog-to-digital conversion samples the signal to represent it digitally as a numerical value. Under-sampling will underrepresent the waveform and make it appear as an “alias” waveform. This cannot be corrected after the digitization, though some machines may have an anti-aliasing filter with a steep roll-off.

Grounding is a method used to reduce noise from the electrical main. Using the ground is essential to eliminate the risk of unsafe potential passage of current through the patient, leading to electrical injury. Patients are not connected to a “true” ground but instead use a ground electrode that electrically (or optically) isolates ground from the power supply. For patient safety, an electrode board having an isolated ground or isoground can be employed instead of the commonly used unit. The isoground limits current flow to ground via the EEG ground electrode to safe levels regardless of any faults that might develop in other connections to the patient. During EEG recording, both the active and reference leads undergo analysis during referential or bipolar recording relative to the common ground electrode.

Amplifiers and filters. One essential function of the EEG machine is to amplify biological signals in voltage generated by the brain (reflected in the gain of an amplifier). The EEG amplifiers are not designed to distort the EEG but, rather, to increase the voltage of the signal and control the low-frequency filter, high-frequency filter, notch filter (60 Hz), and the baseline adjustment for each channel (08). Amplifiers receive input voltage in a dynamic range. They are flexible due to the sensitivity of the units measured in either microvolts per millimeter or millivolts per centimeter. For example, when an EEG is performed using a sensitivity of 7 µV/mm, the defection of the waveforms ranges from 3 to 20 mm for input voltages of 20 to 140 µV (08). In addition, the EEG amplifiers are differential amplifiers and measure the potential difference between paired electrodes. The amplifiers also can suppress common voltages recorded by two electrodes (input 1 and input 2). Electrodes that record a 60 Hz artifact do so because of the capacitance generated between the metallic sensors on the body and electrical sources located in close proximity to each other. Because the power main contains a common voltage, the amplifier function reduces “noise” by common-mode rejection of the common in-phase signals. The common-mode rejection ratio (usually 10,000:1) reflects the relative suppression of the common signals relative to that which is generated by the brain. The Common Mode Rejection Ratio (CMRR) is the ratio of the powers for the differential gain divided by the common-mode gain. This is measured in decibels. Modern EEG machines’ CMRR ranges from 80 dB to 100 dB, though they are unable to suppress all common signals. The CMRMR is measured by connecting a known voltage source to two connectors.

The power supply transforms alternating current acquired from the main power to a lower voltage direct current, usually in the range of 1 to 24 volts (45). The power cord must maintain an intact ground connection to the chassis and a low capacitance in case the connection fails. Today, EEG machines have multiple channels, isolated grounds, high-capacity storage, and software applications designed to enhance source localization. Modern amplifiers include up to 512 referential channels; some have DC low-frequency filters and up to 30,000 Hz sampling rates (bandpass 3000 to 10,000 Hz). Filters remove unwanted components in a frequency-specific manner. Filters act as a circuit, combining a capacitor and resistor (like a voltage divider). Low-frequency filters/high-pass filters facilitate the limits of high-frequency recording by combining the effects of a capacitor and resistor to attenuate low frequencies. A high-frequency filter/low-pass filter is designed with the resistor and capacitor in reverse positions in the circuit. Low-pass filters facilitate both low- and high-frequency components of the signal to pass into the EEG recording. Both high-pass and low-pass filters have a targeted cutoff frequency. This is defined by the point at which the output in volts of the filter is −3 dB (or 0.707) relative to the voltage of the input signal. Newer digital filters and finite impulse response filters may not produce the phase distortion seen with prior filters. Matrices and software to integrate internal switching are possible now to combine functions. Visualization of the signal can be manipulated by gain as the amplification factor of the EEG that reflects output voltage in decibels (dB). Wireless communication now exists from the jack box to the amplifier to “externalize” the system more completely. Additional outputs (with USB ports available) are now able to record oximetry, carbon dioxide monitors, and DC channels among others to integrate more physiological functions with EEG for comprehensive assessment. Software additions assist with spike and seizure identification. Artificial intelligence is evolving to help assist with final interpretation that may be especially useful in underserved, under-represented areas and institutions where high volumes need compression (44). Artificial intelligence and machine learning algorithms are being utilized and compared to expert EEG interpretation to supplement automated seizure detection software. With regards to automated spike detection and EEG interpretation, shallow learning models, such as support vector machines, filter the normal EEG background so that the EEG interpreter is presented with only the candidate interictal epileptiform discharges (03). Deep learning algorithms, such as convolutional neural networks, have become popular for EEG analysis as well (15). Noninvasive wearable devices are capable of automated seizure detection and allow for portable long-term monitoring, using either wrist-worn or wearable surface devices. The devices typically measure data, including heart rate variability, electrodermal activity, surface electromyographic signals, and accelerometry. Trained algorithms analyze the data for automated seizure detection, particularly tonic-clonic seizures (24).

Recording conventions. Electrode impedances should be less than 5 microvolts and balanced with no more than 10 kOhm difference between each electrode pair (30). Polarity convention with differential amplifiers is represented as follows: (a) if input 1 is negative with respect to input 2, there will be an upward deflection; (b) if input 1 is positive with respect to input 2, there will be a downward deflection; (c) if input 2 is negative with respect to input 1, there will be a downward deflection; and (d) if input 2 is positive, there is an upward deflection. Scalp EEG typically captures brain wave signals in frequencies ranging from 1 Hz to 70 Hz. If the frequency range of the recording is too narrow, certain waveforms will not be captured, and if the range is too high, too much noise will be recorded. Thus, EEG machines have the capability to filter high frequencies as well as low frequencies. Using the recommended settings of 1 Hz for low-frequency filters and 70 Hz for high-frequency filters will result in a low probability of a distorted recording. The notch filter or 60 Hz filter should be used only when 60 Hz is observable and all nonessential equipment has been unplugged in an attempt to alleviate line noise. Incorrect filter settings will distort amplitude and interchannel phase of signals so should be changed sparingly.

Digital EEG display. Monitors display the EEG signal quality and depend on adequate resolution. The number of pixels that reflect the points used to represent the display and pitch between them (diagonal distance) has software as a foundation for controlling any video that is combined. Screen sizes of at least 20 inches should be used though often dual monitoring is implemented when video-EEG monitoring is instituted. Screen resolution (eg, 1280 x 1024) may prevent aliasing created by too few pixels and under-sampling (minimum required is 100 pixels/second).

Conclusions. The EEG is fundamental to the accurate diagnosis and management of patients with epilepsy and neurologic problems. Technical aspects of recording optimal EEG signals may be challenging to appreciate from a pragmatic standpoint though fundamental to ensuring an adequate record satisfactory for interpretation. Knowledge of the instrumentation involved in performing EEG is essential to obtaining an optimal recording for clinical use. EEG technology is ever-changing and advancing; however, the basic technical aspects of recording EEG lie at the foundation of applying clinical neurophysiology to patient care.

References

01: Acharya JN, Hani AJ, Thirumala PD, Tsuchida TN. American Clinical Neurophysiology Society Guideline 3: A Proposal for Standard Montages to Be Used in Clinical EEG. J Clin Neurophysiol 2016;33(4):312-6.** PMID 27482795
02: Alvarez V, Rossetti AO. Clinical Use of EEG in the ICU: Technical Setting. J Clin Neurophysiol 2015;32(6):481-5. PMID 26629758
03: Bagheri E, Jin J, Dauwels J, Cash S, Westover MB. A fast machine learning approach to facilitate the detection of interictal epileptiform discharges in the scalp electroencephalogram. J Neurosci Methods 2019;326:108362. PMID 31310822
04: Bodde NM, Brooks JL, Baker GA, Boon PA, Hendriksen JG, Aldenkamp AP. Psychogenic non-epileptic seizures--diagnostic issues: a critical review. Clin Neurol Neurosurg 2009;111:1–9. PMID 19019531
05: Chen Y, Eldar YC, Goldsmith AJ. Shannon Meets Nyquist: Capacity of sampled Gaussian channels. IEEE Trans Inf Theory 2013;59(8):4889-914.
06: Collura TF. History and evolution of electroencephalographic instruments and techniques. J Clin Neurophysiol 1993;10(4):476-504. PMID 8308144
07: Duun-Henriksen J, Baud M, Richardson MP, et al. A new era in electroencephalographic monitoring? Subscalp devices for ultra-long-term recordings. Epilepsia 2020;61(9):1805-17. PMID 32852091
08: Ebner A, Sciarretta G, Epstein CM, Nuwer M. EEG instrumentation. The International Federation of Clinical Neurophysiology. Electroencephalogr Clin Neurophysiol Suppl 1999;52:7-10.** PMID 10590971
09: Faulkner HJ, Arima H, Mohamed A. Latency to first interictal epileptiform discharge in epilepsy with outpatient ambulatory EEG. Clin Neurophysiol 2012;123(9):1732-5. PMID 22621908
10: Feyissa AM, Tatum WO. Adult EEG. Handb Clin Neurol 2019;160:103-24. PMID 31277842
11: Fisher RS, Cross JH, D'Souza C, et al. Instruction manual for the ILAE 2017 operational classification of seizure types. Epilepsia 2017;58(4):531-42. PMID 28276064
12: Goel K, Pek V, Shlobin NA, et al. Clinical utility of intraoperative electrocorticography for epilepsy surgery: a systematic review and meta-analysis. Epilepsia 2023;64(2):253-65. PMID 36404579
13: Gonzalez Otarula KA, Schuele S. Ambulatory EEG-video. Epilepsy Behav 2024;151:109615. PMID 38176091
14: Halford JJ, Sabau D, Drislane FW, Tsuchida TN, Sinha SR. American Clinical Neurophysiology Society Guideline 4: Recording Clinical EEG on Digital Media. J Clin Neurophysiol 2016;33(4):317-9.** PMID 27482787
15: Han K, Liu C, Friedman D. Artificial intelligence/machine learning for epilepsy and seizure diagnosis. Epilepsy Behav 2024;155:109736. PMID 38636146
16: Haneef Z, Yang K, Sheth SA, et al. Sub-scalp electroencephalography: a next-generation technique to study human neurophysiology. Clin Neurophysiol 2022;141:77-87. PMID 35907381
17: Jarrar R, Buchhalter J, Williams K, McKay M, Luketich C. Technical tips: Electrode safety in pediatric prolonged EEG recordings. Am J Electroneurodiagnostic Technol 2011;51(2):114-7. PMID 21809748
18: Kappenman ES, Luck SJ. The effects of electrode impedance on data quality and statistical significance in ERP recordings. Psychophsiology 2010;47(5):888-904. PMID 21809748
19: Kolls BJ, Olson DM, Gallentine WB, Skeen MB, Skidmore CT, Sinha SR. Electroencephalography leads placed by nontechnologists using a template system produce signals equal in quality to technologist-applied, collodion disk leads. J Clin Neurophysiol 2012;29(1):42-9. PMID 22353984
20: McKay JH, Feyissa AM, Sener U, et al. Time is brain: the use of EEG electrode caps to rapidly diagnose nonconvulsive status epilepticus. J Clin Neurophysiol 2019;36(6):460-66. PMID 31335565
21: Mirsattari SM, Davies-Schinkel C, Young GB, Sharpe MD, Ives JR, Lee DH. Usefulness of a 1.5 T MRI-compatible EEG electrode system for routine use in the intensive care unit of a tertiary care hospital. Epilepsy Res 2009;84(1):28-32. PMID 19179047
22: Moura LM, Shafi MM, Ng M, et al. Spectrogram screening of adult EEGs is sensitive and efficient. Neurology 2014;83(1):56-64. PMID 24857926
23: Muraja-Murro A, Mervaala E, Westeren-Punnonen S, et al. Forehead EEG electrode set versus full-head scalp EEG in 100 patients with altered mental state. Epilepsy Behav 2015;49:245-9. PMID 25997637
24: Naganur V, Sivathamboo S, Chen Z, et al. Automated seizure detection with noninvasive wearable devices: a systematic review and meta-analysis. Epilepsia 2022;63(8):1930-41. PMID 35545836
25: Ney JP, van der Goes DN, Nuwer MR, Nelson L, Eccher MA. Continuous and routine EEG in intensive care: utilization and outcomes, United States 2005-2009. Neurology 2013;81(23):2002-8. PMID 24186910
26: Nuwer M, Comi G, Emerson R, et al. IFCN standards for digital recording of clinical EEG. The International Federation of Clinical Neurophysiology. Electroencephalogr Clin Neurophysiol Suppl 1999;52:11-14.** PMID 10590972
27: Olejniczak P. Neurophysiologic basis of EEG. J Clin Neurophysiol 2006;23(3):186-9. PMID 16751718
28: Rubboli G, Parra J, Seri S, Takahashi T, Thomas P. EEG diagnostic procedures and special investigations in the assessment of photosensitivity. Epilepsia 2004;45 Suppl 1:35-9. PMID 14706044
29: Sansevere AJ, Hahn CD, Abend NS. Conventional and quantitative EEG in status epilepticus. Seizure 2019;68:38-45. PMID 30528098
30: Sinha S, Sullivan L, Sabau D, San-Juan D, et al. American Clinical Neurophysiology Society Guideline 1: Minimum Technical Requirements for Performing Clinical Electroencephalography. J Clin Neurophysiol 2016;33(4):303-7.** PMID 27482788
31: Smith SJ. EEG in the diagnosis, classification, and management of patients with epilepsy. J Neurol Neurosurg Psychiatry 2005;76 Suppl 2:ii2–7. PMID 15961864
32: So EL. Interictal epileptiform discharges in persons without a history of seizures: what do they mean? J Clin Neurophysiol 2010;27(4):229-38. PMID 20634716
33: Stone JL, Hughes JR. Early history of electroencephalography and establishment of the American Clinical Neurophysiology Society. J Clin Neurophysiol 2013;30(1):28-44.** PMID 23377440
34: Sutter R, Kaplan PW, Cervenka MC, et al. Electroencephalography for diagnosis and prognosis of acute encephalitis. J Clin Neurophysiol 2015;126(8):1524-31. PMID 25476700
35: Tao JX, Baldwin M, Ray A, Hawes‐Ebersole S, Ebersole JS. The impact of cerebral source area and synchrony on recording scalp electroencephalography ictal patterns. Epilepsia 2007;48(11):2167-76. PMID 17662060
36: Tatum WO. Normal “suspicious” EEG. Neurology 2013;80(1 Supplement 1):S4-11. PMID 23267043
37: Tatum WO. EEG essentials. Continuum (Minneap Minn) 2022;28(2):261-305. PMID 35393960
38: Tatum WO, Desai N, Feyissa A. Ambulatory EEG: crossing the divide during a pandemic. Epilepsy Behav Rep 2021;16:100500. PMID 34778740
39: Tatum WO, Dworetzky BA, Schomer DL. Artifact and recoding concepts in EEG. J Clin Neurophysiol 2011;28:252-63.** PMID 21633251
40: Tatum WO, Halford JJ, Olejniczak P, et al. Minimum technical requirements for performing ambulatory EEG. J Clin Neurophysiol 2022a;39(6):435-40. PMID 35916885
41: Tatum WO, Mani J, Jin K, et al. Minimum standards for inpatient long-term video-EEG monitoring: a clinical practice guideline of the International League Against Epilepsy and International Federation of Clinical Neurophysiology. Clin Neurophysiol 2022b;134:111-128. PMID 34955428
42: Tatum WO, Rubboli G, Kaplan PW, et al. Clinical utility of EEG in diagnosing and monitoring epilepsy in adults. Clin Neurophysiol 2018;129(5):1056-82. PMID 29483017
43: Thirumala PD, Thiagarajan K, Gedela S, Crammond DJ, Balzer JR. Diagnostic accuracy of EEG changes during carotid endarterectomy in predicting perioperative strokes. J Clin Neurosci 2016;25:1-9. PMID 26474501
44: Tveit J, Aurlien H, Plis S, et al. Automated interpretation of clinical electroencephalograms using artificial intelligence. JAMA Neurol 2023;80(8):805-12. PMID 37338864
45: Usakli AB. Improvement of EEG signal acquisition: an electrical aspect for state of the art of front end. Comput Intell Neurosci 2010;630-49. PMID 20148074

Contributors

All contributors' financial relationships have been reviewed and mitigated to ensure that this and every other article is free from commercial bias.

Authors

William O Tatum IV DO FACNS

Dr. Tatum of Mayo Clinic Florida received consulting stipends from Bioserenity and Neurelis and consultant fees from Synergy Medical Solutions.
See Profile
Dawn Radford DO

Dr. Radford of Mayo Clinic Jacksonville has no relevant financial relationships to disclose.
See Profile
Anteneh M Feyissa MD MSc

Dr. Feyissa of the Mayo Clinic Florida received a consulting fee from Neuralis as an advisory board member.
See Profile

Editor

John M Stern MD

Dr. Stern, Director of the Epilepsy Clinical Program at the University of California in Los Angeles, received honorariums from Ceribell, Jazz, LivaNova, Neurelis, SK Life Sciences, and UCB Pharma, and Xenon as advisor and/or lecturer.
See Profile

Former Authors

Gabriel Calado MD
Kirsten Yelvington REEGT CLTM
Valerie Davis R.EEG.T CLTM

This is an article preview.
Start a Free Account
to access the full version.

Nearly 3,000 illustrations, including video clips of neurologic disorders.
Every article is reviewed by our esteemed Editorial Board for accuracy and currency.
Full spectrum of neurology in 1,200 comprehensive articles.
Listen to MedLink on the go with Audio versions of each article.

Questions or Comment?

MedLink, LLC

3525 Del Mar Heights Rd, Ste 304
San Diego, CA 92130-2122

Toll Free (U.S. + Canada): 800-452-2400

US Number: +1-619-640-4660

Support: service@medlink.com

Editor: editor@medlink.com

ISSN: 2831-9125

Technical aspects of EEG

Also Relevant

EEG in encephalopathic conditions
EEG in epilepsy
EEG monitoring in the intensive care unit

Technical aspects of EEG …

Technical aspects of EEG

Cite this article

Introduction

Overview

Key points

Historical note and terminology

Clinical aspects

Description

Indications

Contraindications

Results

Adverse effects

Special considerations

Clinical vignette

Scientific basis

Media

References

Contributors

Authors

Editor

Former Authors

This is an article preview.
Start a Free Account
to access the full version.

Questions or Comment?

Also in This Category

Fenfluramine

Self-limited (familial) infantile epilepsy

Jacksonian seizures

Hippocampal and parahippocampal seizures

Sleep hyperkinetic (hypermotor) epilepsy

Alcohol withdrawal seizures

Epilepsy surgery in children

Functional/dissociative seizures

Technical aspects of EEG

Cite this article

Introduction

Overview

Key points

Historical note and terminology

Clinical aspects

Description

Indications

Contraindications

Results

Adverse effects

Special considerations

Clinical vignette

Scientific basis

Media

References

Contributors

Authors

Editor

Former Authors

This is an article preview. Start a Free Account to access the full version.

Questions or Comment?

Also in This Category

Fenfluramine

Self-limited (familial) infantile epilepsy

Jacksonian seizures

Hippocampal and parahippocampal seizures

Sleep hyperkinetic (hypermotor) epilepsy

Alcohol withdrawal seizures

Epilepsy surgery in children

Functional/dissociative seizures

This is an article preview.
Start a Free Account
to access the full version.