Which of the following is a diagnostic use of the brain scanning technique electroencephalography?

What Is an EEG (Electroencephalogram)?

An EEG, or electroencephalogram, is a test that records the electrical signals of the brain by using small metal discs (called electrodes) that are attached to your scalp. Your brain cells communicate with each other using electrical impulses. They’re always working, even if you’re asleep. That brain activity will show up on an EEG recording as wavy lines. It’s a snapshot in time of the electrical activity in your brain. 

EEG Uses

EEGs are used to diagnose seizures related to: 

• Brain tumors
• Brain damage from a head injury
• Brain dysfunction from various causes (encephalopathy)
• Inflammation of the brain (encephalitis)
• Seizure disorders including epilepsy
• Sleep disorders 
• Stroke

An EEG may also be used to determine if seizures caused a coma, if there is no longer brain activity, or to find the right level of anesthesia for someone in a coma.

EEG Risks

EEGs are safe. If you have a medical condition, talk with the doctor about it before your test.

If you have a seizure disorder, there’s a slight risk that the flashing lights and deep breathing of the EEG could bring on a seizure. This is rare. A medical team will be on hand to treat you immediately if this happens.

In other cases, a doctor may trigger a seizure during the test to get a reading. Medical staff will be on hand so the situation is closely monitored.

Preparing for an EEG

There are some things you should do to prepare for EEG:

• Don’t eat or drink anything with caffeine for 8 hours before the test.
• Your doctor may give you instructions on how much to sleep if you’re expected to sleep during the EEG.
• Eat normally the night before and day of the procedure. Low blood sugar could mean abnormal results.
• Let your doctor know about any medications -- both prescription and over-the-counter -- and supplements you're taking.
• Wash your hair the night before the test. Don't use any leave-in conditioning or styling products afterward. If you are wearing extensions that use glue, they should be removed.

EEG Procedure

1. You lie down on the exam table or bed, and a technician puts about 20 small sensors on your scalp. These sensors, called electrodes, pick up electrical activity from cells inside your brain called neurons and send them to a machine, where they show up as a series of lines recorded on paper or displayed on a computer screen.
2. Once the recording begins, you’ll be asked to remain still.
3. You'll relax with your eyes open first, then with them closed. The technician may ask you to breathe deeply and rapidly or to stare at a flashing light, because both of these can change your brainwave patterns. The machine is only recording the activity of the brain and doesn’t stimulate it.
4. It's rare to have a seizure during the test.
5. You can have an EEG at night while you're asleep. If other body functions, such as your breathing and pulse, are also being recorded, the test is called polysomnography. 
6. In some cases, you may be sent home with an EEG device, which will either send the data directly back to your doctor's office or record it for later analysis.

After an EEG

Once the EEG is over, the following things will happen:

• The technician will take the electrodes off and wash off the glue that held them in place. You can use a little fingernail polish remover at home to get rid of any leftover stickiness.
• Unless you're actively having seizures or your doctor says you shouldn't, you can drive home. But if the EEG was done overnight, it's better to have someone else drive you.
• You can usually start taking medications you'd stopped specifically for the test.
• A neurologist, a doctor who specializes in the brain, will look at the recording of your brain wave pattern.

EEG Results

Once the EEG results have been analyzed, they will be sent to your doctor, who will go over them with you. The EEG will look like a series of wavy lines. The lines will look different depending on whether you were awake or asleep during the test, but there is a normal pattern of brain activity for each state. If the normal pattern of brain waves has been interrupted, that could be a sign of epilepsy or another brain disorder. A normal EEG does not mean you do not have epilepsy. Your doctor will do other tests to confirm a diagnosis.

Abstract

Electroencephalography (EEG) provides a window into the dynamic function of the central nervous system (CNS). It is the only measure that allows differentiation within the spectrum of consciousness. EEG recording requires care and attention to detail regarding electrode application, equipment preparation, and the recognition and elimination of artifact. EEG allows for analysis of data in terms of both time (i.e., frequency) and voltage (i.e., amplitude) domains. Other analyses include describing the morphology and temporal distribution of events. When used in polysomnography (PSG), EEG allows for both microanalysis (e.g., specific frequencies and waveforms) and macroanalysis (e.g., whether the patient is awake or asleep, whether pathologies are present) of sleep. EEG can also differentiate between wakefulness, sleep, coma, and CNS silence (brain death). EEG can be used in clinical settings to diagnose CNS pathology and is included in PSG, along with multiple other physiological parameters to distinguish sleep and wake, and to identify sleep stages. EEG is also used in a variety of research protocols. Traditionally, EEG is performed in well-controlled laboratory settings; however, portable monitoring and long-term monitoring have also become common with recent advances in technology.

Window on the Mind

Human electroencephalography (EEG) provides a convenient, but often opaque, ‘window on the mind,’ allowing observations of electrical processes near the brain surface. The outer brain layer is the cerebral cortex, believed to be largely responsible for cognition: perception, memory, thinking, emotions, actions, and behaviors. Cortical processes involve electrical signaling between neurons that change over many times in the 10 ms (0.01 s) range. EEG is the only widely available technology with sufficient temporal resolution to follow these quick dynamic changes.

EEG can be recorded using electrodes placed inside the skull to study nonhuman mammals or human epilepsy patients. Such intracranial recordings provide measures of cortical dynamics at small spatial scales, dependent on electrode size. However, there are significant limitations to intracranial EEG recording for studies of cognition and behavior. Intracranial recordings in humans are mostly limited to patients with intractable epilepsy, often in preparation for brain surgery. These recordings are called electrocorticograms (ECoGs). ECoG recordings are usually obtained only over a very limited portion of the cortex, areas which vary widely across individuals, partly guided by EEG recordings of epileptic activity using electrodes placed on the scalp prior to surgery.

In both clinical and research studies, EEG is nearly always recorded from electrodes placed on the scalp. Each scalp electrode records electrical activity at large scales, measuring electric currents (or potentials) generated in cortical tissue containing about 30 million to 500 million neurons. Luckily, these large-scale estimates provide important measures of brain dysfunction for clinical work and cognition or behavior for basic scientific studies. Human ‘mind-measures’ are easily obtained at the large scale of scalp recordings. EEG monitors the state of consciousness of patients in clinical work or experimental subjects in basic research. Oscillations of scalp voltage tell a very limited but important part of the story of brain functioning. For example, states of deep sleep, coma, or anesthesia are mostly associated with very slow EEG oscillations and larger amplitudes. Modern signal analyses allow for identification of distinct sleep stages or quantitative measures of the depth of anesthesia. More sophisticated experimental designs and methods of signal analysis have revealed robust connections to detailed cognitive events.

On the other hand, EEG spatial resolution is poor, compared to modern brain functional imaging methods such as PET and MRI. But these latter methods have very poor temporal resolutions on the timescale of seconds and thus do not offer detailed information about the rapid neural dynamics available to EEG. The related technology, magnetoencephalography (MEG), consists of recordings of the magnetic field generated by brain current sources. MEG also provides high temporal resolution and low spatial resolution, similar to EEG. MEG is preferentially sensitive to brain current sources oriented tangential to the scalp surfaces, which are typically located in the sulcal walls (folded cortex), while EEG is more sensitive to radial sources that are mainly located in the gyral surfaces (see Figure 1).

Headache

Electroencephalography has little relevance to the diagnosis of migraine. In uncomplicated cases, the EEG is usually normal, or shows only minor nonspecific changes between and during migrainous attacks. Focal or unilateral slow-wave disturbances are common, however, particularly in patients developing lateralized aura or neurologic deficits in association with their attacks. Such localized abnormalities usually settle rapidly once the clinical disturbance has resolved, unless infarction has occurred or there is an underlying structural abnormality. Paroxysmal epileptiform activity sometimes is found, but the proportion of cases with such a disturbance varies greatly in different series. It is unclear whether the association of migraine with such paroxysmal activity is genetic or related to cerebral ischemic damage. The EEG disturbance, in itself, is insufficient evidence to permit the headaches to be regarded as the manifestation of an epileptic disorder.

There is always some concern that an underlying structural lesion may have been missed in patients with chronic headache syndromes that fail to respond to medical treatment. Although the EEG has been used by some as a screening procedure for patients requiring further investigation, the EEG is less sensitive than cranial CT scanning or MRI and—given the implications of delay in the diagnosis of an intracranial mass lesion—it is hard to justify its use in place of imaging studies when these modalities are readily available and intracranial pathology is suspected clinically.92

There is little, if any, evidence that the EEG has a useful role in the routine evaluation of patients presenting with headache, and it is not helpful for predicting prognosis or in selecting therapy.92

Questions

1

Brain activity recorded with electroencephalography (EEG) is commonly obscured by the following factors:

Electrical activity from scalp electromyography

Skull

Distance between the brain region of interest and the electrodes

Fluid surrounding the brain

All of the above

Electrical activity recorded at the scalp arises from:

Muscles of the scalp

Extracellular currents generated by the postsynaptic potentials of neurons

Eye movements

Electrode “pops”

All of the above

According to the 10–20 system of electrode naming, odd-numbered electrodes indicate which location?

Temporal lobe

Frontal lobe

Occipital lobe

Left hemisphere

Right hemisphere

Electrode Cz is located where, according to the 10–20 system of electrode placement?

Central on the left

Central on the midline

Central on the right

Parietally on the left

Parietally on the right

Respiratory artifact seen on EEG may be attenuated by:

Increasing the high-frequency filter

Decreasing the high-frequency filter

Increasing the low-frequency filter

Decreasing the low-frequency filter

Adjusting the nasal thermistor

The following EEG frequencies are typically seen in a normal awake adult:

Alpha and theta

Theta and delta

Alpha and beta

Alpha, beta, and delta

Alpha, beta, delta, and theta

The posterior dominant (“alpha”) rhythm may be absent in a normal awake adult owing to:

Eye opening

Concentration

Hand movement

Eye opening or concentration

Eye opening or hand movement

By applying the notch filter, you achieve the following desirable and undesirable outcomes:

Desirable: 60 Hz interference is decreased in the recording.

Undesirable: Other signals close to this frequency are slightly attenuated and can be difficult to see.

Desirable: 60 Hz interference is removed from the recording.

Undesirable: There are no undesirable outcomes. The notch filter should always be left on.

Desirable: All inconsequential information is removed (as in viewing only the useful notch).

Undesirable: There are no undesirable outcomes. The notch filter should always be left on.

Desirable: All inconsequential information is removed (as in viewing only the useful notch).

Undesirable: It is possible to miss important information found outside of the notch range.

A patient is described as having a seizure. After viewing the video and EEG (six channel) polysomnography (PSG) recording, a classically appearing tonic-clonic seizure is observed; however, there is no electrographic evidence of the event. Which is the most likely explanation?

The electrographic correlate of the seizure was obscured by artifact.

The patient became disconnected during the seizure.

Some generalized seizures do not have an EEG correlate.

High-amplitude EEG activity during seizures frequently blocks the recording.

You observe a high-amplitude wave that has a morphology consistent with a spike in one electrode pairing. The activity in all adjacent electrodes appears to be normal. What is the most likely conclusion?

You are observing a spike that suggests a risk of epilepsy.

You are observing electrode “pop.” If it were an epileptic spike, there would be an electrical field, and similar activity would also be seen (at lower amplitude) in adjacent electrodes.

This is likely a vertex wave.

There is not enough information here to decide.

If the low-frequency filter is set on 1 Hz and the high-frequency filter is set on 70 Hz, how will the signal be altered?

All signals with frequencies below 1 Hz and above 70 Hz will be completely removed from the recording.

Those signals with frequencies below 1 Hz and above 70 Hz will be attenuated gradually, starting at the set number.

Those signals with frequencies below 1 Hz and above 70 Hz will be attenuated gradually, starting below/above the set number.

Those signals with frequencies of 1 Hz and 70 Hz will be removed from the recording. All other signals will remain unaltered.

When running an EEG/PSG concurrently, what type of adhesive is most effective for keeping electrodes in place?

Colodian

Conductive paste

Most electrodes are needle type and hold themselves in place.

A and B

K-complexes and sleep spindle activity are best viewed by using what electrodes?

Central electrodes

Occipital electrodes

Frontal electrodes.

Temporal electrodes

The observed amplitude of EEG activity is influenced by which of the following?

The interelectrode difference

The amount of brain involved in the discharge

The skin and skull thickness

All of the above

What is the standard paper speed for reading EEG?

10 mm/sec

10 sec/page

30 mm/sec

B and C

A signal is considered to be in the alpha range if:

It has a frequency of 8–12 Hz.

It has an amplitude that is larger than beta but smaller than gamma.

It is sinusoidal in nature.

None of the above

When referring to the amplitude, frequency, and morphology of waveforms, how do the right and left hemispheres compare to one another in a normal patient?

They appear symmetrical.

The dominant hemisphere is always at least twice the amplitude of the nondominant hemisphere.

It has not been well established. Sometimes they are symmetrical, and at other times they are not.

The nondominant hemisphere is always at least twice the amplitude of the dominant hemisphere.

If mu rhythm is observed, what action should be taken?

The attending physician should be notified so that the patient is admitted for treatment.

This is a benign waveform.

The duration and amplitude should be noted and should be emphasized in the report.

The term mu is outdated. What was once referred to as mu is now referred to as spiky alpha.

Polymorphic focal slowing is typically indicative of which of the following?

A structural lesion in that area

It is a normal feature of sleep.

An ongoing seizure

A and C

None of the above

Nocturnal epileptiform activity is seen least in which state?

Rapid eye movement (REM) sleep

Wakefulness

Slow wave sleep

Light non-REM (NREM) sleep

In what channels are eye movements most often seen?

Fp1, Fp2, F7, and F8

C3 and C4

O1 and O2

Eye movements are usually observed equally in all EEG channels.

Questions 22 and 23 refer to Figure 17-1, which shows an EEG in typical PSG montage shown at the top, with a portion of the identical epoch in the longitudinal bipolar EEG montage below.

22

Differences between a typical PSG montage and a longitudinal bipolar EEG montage include:

Waveform amplitudes in the PSG montage may appear larger because of the greater interelectrode differences.

The PSG montage allows for more discrete localization of cerebral discharges because a larger area of the brain is covered.

The “paper speed” for typical EEG reading is slower, thus increasing the amount of seconds of recording per page.

Reducing the high-frequency filter to 30 Hz will have greater effects on the typical PSG reading speed and cause frequencies of activity to decrease.

According to the EEG recording, which of the following is true about the patient?

The patient is having a generalized seizure.

There are abundant epileptiform discharges, but no evolution; therefore this is not a seizure.

The patient is in stage 1 sleep.

The patient is awake and alert.

Questions 24 and 25 refer to Figure 17-2, which shows an epoch in a typical PSG montage shown at the top, with the middle of the epoch shown in longitudinal bipolar montage below. A number of events are indicated.

24

The arrowhead is pointing to:

Muscle artifact

Focal beta activity starting in the right frontal region that is spreading in field, evolving in frequency and increasing in amplitude to meet criteria for a seizure

Focal beta activity starting in the right anterior temporal region that is spreading in field, evolving in frequency and increasing in amplitude to meet criteria for a seizure

Nystagmus

The large, dark arrows are pointing to:

Focal spikes and spike-wave discharges

Vertex waves

“Pop” artifact

None of the above

32 What are the characteristics of focal epileptiform spikes?

A spike is an EEG transient with a duration of less than 70 msec. The transient may occur alone, but frequently a slow wave follows, forming a spike and slow-wave complex. The duration of the slow wave may last from 150 to 350 msec. The spike transient may be monophasic or polyphasic. The polarity of most focal epileptiform spikes recorded at the scalp is surface negative. Surface positive spikes rarely occur in patients with epilepsy (Figure 25-19).

KEY POINTS:

Electroencephalography

The normal adult EEG, relaxed with eyes closed, is characterized by 9 to 11 cycles per second activity in the back of the brain (occipital lobes) called the alpha rhythm.

Each stage of sleep has a very characteristic EEG pattern.

Periodic lateralizing epileptiform discharges (PLEDs) on an EEG imply an acute, large lesion involving one hemisphere, such as a stroke or focal encephalitis.

The 3 per second spike and wave pattern on an EEG is usually seen in patients with absence seizures.

The finding on an EEG that is most suggestive of focal epilepsy is a very brief (less than 70 msec) transient deflection called a spike.

The EEG is one of the most important tests to confirm brain death.

Introduction

Electroencephalography (EEG) eavesdrops on the brain's electrical signals through recording electrodes on the scalp. Traditional routine EEG is viewed as voltage tracings recorded from two dozen standardized scalp sites.

Quantitative electroencephalography (QEEG) refers to digital analysis and measurements made on the routine EEG signals. There are many types of QEEG. One involves a search through long portions of EEG to find epileptic spikes and seizures. Another is EEG frequency analysis, with the results being compared to prior or normative values. Topographic scalp maps or three-dimensional brain maps can display EEG features, a process often labeled EEG brain maps. Certain techniques are used in clinical practice. Many other techniques are used just in research.

Abstract

Electroencephalography (EEG) is a specific investigation to support the diagnosis of epilepsy, demonstrating interictal epileptiform activity in the majority of individuals with epilepsy. The EEG can also help classify the epilepsy as focal or generalized, and can suggest certain epileptic syndromes. However, epileptiform activity is absent in the first EEG in approximately half of affected individuals and the interictal EEG remains normal in about 10%. Prolonged EEG recordings increase the odds of finding epileptiform activity and also provide the opportunity to capture ictal discharges for more definitive diagnosis and classification. Video-EEG (V-EEG) additionally allows correlation of clinical and EEG abnormalities and analysis of seizure semiology. V-EEG has become an essential element of the presurgical evaluation for localization of the epileptogenic zone, but confidence in the EEG data requires congruence with other presurgical tests, particularly magnetic resonance imaging. Interictal slow activity defines a functional deficit zone, interictal epileptiform discharges define the irritative zone, ictal EEG onset defines the ictal onset zone, and the analysis of seizure semiology on video helps define the symptomatogenic zone. The EEG pattern and frequency at ictal onset can improve localization and may help predict seizure outcome. The EEG is also crucial in the diagnosis of nonconvulsive status epilepticus. The EEG has pitfalls and limitations, and has to be used in conjunction with clinical and imaging data to avoid misdiagnosis of epilepsy.

Electroencephalography

Electroencephalography (EEG) recordings are used to characterize globally the electrical activity of the brain. The activity is recorded with scalp electrodes placed equidistantly on the head. A normal EEG recording is characterized by well-defined rhythms that have specific frequencies. EEG is used primarily in the diagnosis of epilepsy, as the analysis of the traces can help identify the seizure locus as well as, in some cases, the type of epilepsy. EEG is also useful in ventilated unconscious patients to detect seizures, as in these patients there may not be any external evidence of seizure activity. It is also used occasionally to confirm brain death, when it can show whether the electrical activity of the brain has ceased or not. EEG can be used in combination with MRI.

Definition and History

Electroencephalography (EEG) is a technique used in the diagnosis and management of different forms of epilepsy and some movement disorders. EEG measures the electrical activity of the brain as a function of voltage potentials between different regions on the scalp. The electrical activity recorded is a summation of the activity of a large number of neurons in the cerebral cortex immediately beneath the skull. This registration provides useful information on both the normal activity of the brain in different states (e.g., sleep and wakefulness) and abnormal activities resulting from a variety of disease processes.

EEG has its origins in the long history of electrophysiology experimentation. However, the person generally credited with the first application of EEG to human subjects is Hans Berger (1873–1941), a German neuropsychiatrist, who began recording EEG from people in 1924. The use of EEG has increased significantly in recent decades, as technology has improved and new applications have been discovered.

ELECTROPHYSIOLOGY

Electroencephalography (EEG) is helpful in the evaluation of seizure disorders and metabolic encephalopathy and, to a lesser extent, for documentation of regional physiological malfunctions. In patients with psychosis, the EEG should be normal, whereas metabolic disorders can cause disorganization and generalized slowing. The EEG can reveal physiological abnormalities that may not be reflected on structural imaging studies. Old trauma, a postictal state, or migraine headache may be associated with behavioral abnormalities and may cause focal EEG findings when the MRI is normal. Rarely, disorders of emotion, mood, or thought with “subclinical seizures” or complex partial status epilepticus may be diagnosed only with EEG. The use of evoked responses in neuropsychiatric disorders remains a research tool except when organic explanations such as multiple sclerosis are being actively considered.