Unit 3 112 yamada and meng ch 6 Principles of Visual Analysis of EEG
FIGURE 6-14 | EEG of a 10-year-old girl with a history of epilepsy, showing slow background activity consisting of irregularly mixed theta-delta activity but without focal finding in the awake state (A) Not shown
. In sleep, the focal feature becomes evident by consistent depression of sleep spindles on the left (the spindles in the right hemisphere are indicated in the box) indicating focal pathology (B) (in addition to bilateral cerebral dysfunction). Note the isolated spike discharges from the left hemisphere, maximum in the frontocentral region (indicated by the asterisk).
4 problems
1) Depression of sleep spindles on left. 2) Sharp discharge from left temporal region. 3) Sharp discharge from left parietal region that is independent from left temporal sharp discharges. 4) Depressed background and faster activities on the left hemisphere.
What are the two ways slow waves, usually consisting of delta activity, are categorized?
1) Serial rhythmic (monomorphic) 2) Serial irregular (polymorphic)
Abnormal activity in adults can reach as high as how many microvolts?
1,000 μV
What is the alpha rhythm in children?
100 to 200 μV.
Beta wave frequency is:
14 to 30 Hz
Gamma wave frequency is:
30 to 80 Hz.
Theta wave frequency is:
4 to 7.5 Hz
Typical adult alpha amplitude is?
40 to 100 uV and usually less than 100 mV.
Alpha wave frequency is:
8 to 13 Hz
Most normal adults, during the awake state, have an alpha rhythm faster than:
9 hz.
Delta wave frequency is:
< 4 Hz
A burst consists of? (purple book)
A burst consists of a stereotyped rhythmic spike and wave complex lasting a few to several seconds. Bursts may also consist of various irregularly mixed waves called polymorphic bursts
A burst is:
A burst is a group of mixed waves that could be either a stereotyped sequence of waves (monomorphic, monorhythmic, or serial rhythmic) or a mixture of various waveforms (polymorphic or serial irregular).
Burst glossary definition is:
A group of waves with a minimum of four phases and duration longer than 500 ms which appear and disappear abruptly and are distinguished from background activity by differences in frequency, form and/or amplitude. Comments: (1) term does not imply abnormality. (2) Not a synonym of paroxysm (see paroxysm).
Sometimes, posterior alpha rhythm may also appear as a mu-shaped form when associated with beta activity. This occurs because:
A mu waveform is a mixture of alpha and beta activities.
Mu rhythm (other quizlet. https://quizlet.com/46444675/eeg-terminology-aset-8-flash-cards/)
A normal variant central rhythm, having the morphology of rows of the letter "m" (mmmmmmmm)or the letter "u" (uuuuuuuuu). A mu rhythm is attenuated by real or imagined contralateral motor activity. If the mu rhythm is on the left, having the patient make a fist with the right hand will attenuate it. (even thinking about making a fist with the right hand will attenuate it)
Bancauds phenomenon:
A phenomenon that occurs when only one side of the posterior dominant rhythm attenuates with eye opening. The abnormal side is the one in which alpha does not attenuate. The slow waking background activity often seen in patients with dementia may not show reactive changes when the eyes are open.
A more accurate amplitude measurement may be made by using what?
A referential derivation, assuming that the reference electrode is relatively "inactive."
What are serial irregular (polymorphic) waves?
A series of slow waves having different amplitude, frequency, or waveform. This pattern is often seen as a localized (focal) slow wave in patients with a focal brain lesion or pathology
A transient is:
A transient is a single wave consisting of a brief mono-, bi-, or triphasic waveform.
EEG Handbook: Both spikes and sharp waves are generated where?
AT the top of the cortical gyrus and have a polarity that is most often negative at the surface of the human scalp.
Focal slowing often becomes more distinct in .
AWAKE than in sleep. It is not uncommon that focal EEG reflecting focal pathology in awake state totally disappears in sleep. In some cases, however, a focal feature is not evident in the awake EEG but becomes apparent in sleep expressed by depressed sleep spindles
Abnormal activity could reach as high as how many microvolts.
Abnormal activity could reach as high as 1,000 microvolts.
An example of a monomorphic paroxysmal burst is represented by the 3-Hz spike-wave discharge (GSW* = generalized spike-wave), which is a diagnostic pattern for?
Absence seizures.
The basic principle of normal EEG activity is the symmetry between homologous electrode pairs during both awake and asleep states. The amplitude, frequency, waveform, and amount or incidence of activities should be symmetric overall between two homologous derivations. Give an example of homologous electrodes not being symmetrical:
Amplitude of the alpha rhythm is often higher in the right than in the left occipital region. Also, the timing of the alpha phase is not exactly the same, that is, not synchronous.
What should the frequency of the dominant occipital rhythm be in a 3 y/o?
An alpha rhythm consistently at or less than 8 Hz during the awake state is abnormally slow at any age except in children less than 3 or 4 years-old. (page 86) Quiz answer was 7 to 8 Hz.
Technical problems of homologous electrodes can include:
An erroneously short interelectrode distance, a salt bridge (shorting of two electrodes by excessive electrode paste), mistakenly recorded parameters, such as sensitivity or filter settings.
What is an evoked potential?
An evoked potential test measures the time it takes for nerves to respond to stimulation.
What are two examples of IRDA?
An example is FIRDA (frontal intermittent rhythmic delta activity) or frontally predominant RDA* often seen in patients with diffuse encephalopathy. Another example of IRDA is OIRDA (occipital intermittent rhythmic delta activity) or occipitally predominant RDA*, which is commonly seen in children, especially in patients with absence seizure.
An example of error in electrode placement. The longitudinal montage showed depressed activity in channel 3 as compared to homologous derivation (channel 7) (A). This was due to P3 electrode placement error with shorter interelectrode distance between C3 and P3 (shown by box), as compared to the homologous electrode pair. Adjusting the electrode placement corrected the asymmetry (B).
An example of error in electrode placement. The longitudinal montage showed depressed activity in channel 3 as compared to homologous derivation (channel 7) (A). This was due to P3 electrode placement error with shorter interelectrode distance between C3 and P3 (shown by box), as compared to the homologous electrode pair. Adjusting the electrode placement corrected the asymmetry (B).
Which group of people has the highest amplitude of alpha?
Children. Most alpha in adults is between 40-100 uV and is higher at 100-200 in children. Hypsarrhythmia can be as high as 1,000 uV.
The amplitude measured in a bipolar recording does not reflect the true (absolute) amplitude of activity from either electrode because the EEG records what?
EEG records the amplitude difference between the two electrodes.
The alpha rhythm is specifically designated as the posterior background rhythm and is attenuated by
Eye opening.
FIGURE 7-1 | Typical normal alpha rhythm during the eyes-closed awake state in a 35-year-old man. Note attenuation of alpha rhythm by eyes opening. (A) is a referential montage and (B) is a longitudinal bipolar montage. (A and B are the same EEG samples.)
FIGURE 7-1 | Typical normal alpha rhythm during the eyes-closed awake state in a 35-year-old man. Note attenuation of alpha rhythm by eyes opening. (A) is a referential montage and (B) is a longitudinal bipolar montage. (A and B are the same EEG samples.)
What is this an example of in the image?
FIRDA
Polymorphic slow waves are often seen in:
Focal pathology (not epilepsy as was in Q)
FIRDA is etiologically nonspecific and may be seen in any diffuse encephalopathy of various severities. If FIRDA is due to a hemispheric lesion, it more likely reflects a
Frontal lobe lesion.
Slower frequency activity has ____________amplitude.
Higher
What wave form is characterized by extremely high amplitude slow waves seen in children with infantile spasms or West syndrome?
Hypsarrhythmia.
Hypsarrhythmia on EEG
Infantile spams, most associated with MR- mental retardation. Infantile spasms is one of the "catastrophic childhood epilepsies" because of the difficulty in controlling seizures and the association with mental retardation.
Examples of extremely high amplitude slow waves in children are:
Infantile spasms, West syndrome.
FIGURE 6-13 | Irregular delta slow waves in the left hemisphere, more prominent in the temporal than parasagittal region in a patient with stroke in the left hemisphere. Note that the delta activity is maximum in the F7 and T3 electrodes with phase reversal between Fp1-F7 and T3-T5 (indicated by arrows) with equipotential activity between F7 and T3 electrodes (indicated by the line) (A). However, background alpha rhythm is well preserved bilaterally. The above distinct focal slow waves become unrecognizable in sleep (B).
See image in previous term.
Examples of transients are spike or sharp discharges, which are defined as:
Sharply contoured waves (distinguishable from the background activity), waveform duration of less than 70 ms for SPIKE, and 70 to 200 ms for sharp waves
Alpha rhythm in adults is usually less than 100 microvolts. Most of the alpha amplitude in adults is how many microvolts?
Most of the alpha amplitude in adults falls within 40 microvolts to 100 microvolts range and is higher at 100 to 200 microvolts in children.
A surface negative, wicket-type rhythm found in the central head regions is known as ____.
Mu rhythm.
An alpha frequency activity with a pointed negative polarity at the central electrodes is called:
Mu rhythm. Wicket rhythm. rhythm en arceau. All of these.
Vertex waves have a negative polarity at the vertex and are typically seen in?
N1 and N2 sleep.
All bursts are abnormal. T or F.
Not all bursts or transients are abnormal. There are many physiological bursts or transients, especially in sleep. Whether these are normal or abnormal is dependent on when and where a given discharge appears,
FIGURE 6-7 | Physiological V wave in stage II sleep (A) and focal epileptiform discharges (B) during awake state in a 40-year-old patient with history of epilepsy.
Note the similarity of the sharp waveform but with a different distribution; bilaterally symmetric for the physiological V waves (shown in box) (A) and lateralized to the right hemisphere for the epileptiform discharges (shown in box) (B). 40-year-old, stage 2 sleep
What is this wave in the image?
OIRDA
Is OIRDA associated with epilepsy or encephalopathy?
OIRDA is present almost exclusively in children and is associated with epilepsy but not acute encephalopathy. OIRDA has clinical importance distinctly different from frontal intermittent rhythmic delta activity.
A burst is characterized by the following features Except: A group of waves paroxysmal discharges occurs only in sleep - no could be normal or abnormal.
Occurs only in sleep - false.
Increased delta activity in response to arousal stimulus in a comatose patient is:
Paradoxical arousal response. Paradoxical arousal describes a change, in the opposite direction, to a pattern dominated by higher-amplitude, lower-frequency waveforms (delta waves).
In cases of mild encephalopathy, background activity is preserved, and in severe encephalopathy, background activity is
Suppressed. FIRDA is more common in metabolic or other diffuse encephalopathies than in those with a focal deep seated lesion.
An amplitude asymmetry between homologous electrodes in a bipolar montage may be due to:
Technical problems rather than true amplitude asymmetry.
When recording an EEG in a comatose patient, it is important to evaluate EEG reactivity. Technologists are allowed to do the following, EXCEPT: -Open and close eyes. -Deliver loud noise. -Pinch fingers or toes. -Temporarily discontinue the ventilator. - no
Temporarily discontinue the ventilator - duh
Phase
The Number of Phases. Number of Phases = 1 + number of baseline crossings of the typical discharge. In this case there are a total of 2 baseline crossings, therefore the number of phases is 1 + 2 = 3 phases. A phase is the part of the signal above or below the imaginary baseline. In this case, phase 1 (pink) is above, phase 2 (blue) is below, and phase 3 (yellow) is above again.
Alpha rhythm usually appears as a repetition of similar waveforms or rhythmically recurring waves, with waxing and waning amplitude changes, but not exactly sinusoidal. Alpha activity in the central electrodes usually has a different waveform than the posterior alpha rhythm. What is the difference?
The central electrodes have a pointed negative peak followed by a rounded positive phase forming a wicket-shaped appearance often referred to as "mu rhythm" (synonyms: wicket rhythm, comb rhythm, and rhythm en arceau)
Occasionally, a seemingly bilaterally synchronous spike/wave discharge may indeed have an onset on one hemisphere, which is more readily visible when viewing at a faster sweep speed (60 mm/s or 5 s/page instead of the standard 30 mm/s or 10 s/page
The most distinctive electroencephalographic pattern of idiopathic epilepsy in childhood is the 2.5 to 3.5 cycle-per-second (cps) spike wave associated with the "absence" seizure. This discharge is abrupt in onset, bilateral, nearly synchronous, and of nearly equal amplitude in the two hemisphere. It is often precipitated by hyperventilation and photic stimulation.
Does a spike discharge or sharp discharge have a higher correlation with a seizure diagnosis?
The spike discharge has higher correlation with seizure diagnosis than the sharp discharge.
People with Aicardi syndrome have absent or underdeveloped tissue connecting the left and right halves of the brain (agenesis or dysgenesis of the corpus callosum ). When do the seizures begin?
They have seizures beginning in infancy (infantile spasms), which tend to progress to recurrent seizures (epilepsy) that can be difficult to treat.
Sweeps are:
Time that the EP response is recorded from stimulus through entire response
Temporal factors relate to:
Timing.
What is the procedure to test the level of consciousness?
To test this, the EEG technologist should ask the patient several simple questions such as the date, names of the presidents or states, counting backwards, etc., during the recording.
What are transients and bursts?
Transients and bursts are paroxysmal activities that appear and disappear suddenly and are clearly distinguishable from the ongoing and sustained EEG activities.
Many EEG patterns are asynchronous in premature babies. True or False?
True
Alpha blocking, a phenomenon where the alpha rhythm is reduced by attention to a visual, auditory, tactile or cognitive stimulus, is one of the most prominent features of human electroencephalography (EEG) signals. True or False?????
True.
If the patient is sleepy or stuporous, it is important to record at least part of the EEG during a time when the patient is at the highest level of consciousness. True or False?????
True.
Sleep spindles are normally asynchronous until the age of 1 year. True or False???
True.
The slow waking background activity often seen in patients with dementia may not show reactive changes when the eyes are open. True or False???
True.
What are V waves?
V waves are sharp waves that occur during sleep. They are largest and most evident at the vertex bilaterally and usually symmetrically. They show phase reversal at the vertex. V waves tend to occur especially during stage 2 sleep and may be multiple. Often, they occur after sleep disturbances (eg, brief sounds) and, like K complexes, may occur during brief semiarousals.
Discharge glossary definition:
Waveforms with no more than 3 phases (i.e. crosses the baseline no more than twice) or any waveform lasting 0.5 s or less, regardless of the number of phases. Interpretive term of action potentials and post-synaptic potentials commonly used to designate interictal epileptiform and seizure patterns
WHich of the following terms is NOT a synonym for wicket rhythm?
Wicket spikes.
Is this a FIRDA image?
Yes
Example of a spatial factor:
a vertex sharp wave is a sharply contoured transient spatially maximum at the midline (vertex) with symmetrical spread to the parasagittal regions in normal sleep
An alpha rhythm consistently at or less than 8 Hz during the awake state is:
abnormally slow at any age except in children less than 3 or 4 years old.
Alpha rhythm overlying the occipital lobes of patients at rest with their eyes closed, and loss of that rhythm when they open their eyes, indicates
an intact visual system.
In addition to examining the amplitude, frequency, and waveform of a given activity, it is important to assess what?
the timing (temporal factor) and location (spatial factor) of the activity.
Asynchrony means that
the waveforms of one hemisphere do not occur at the same time as those over the other, implying different phase relationships between waves on either side, but this is rarely noticed unless there is a difference in the underlying frequency between hemispheres.
The frequency may be measured or estimated by counting the number of waves occurring within 1 second, as long as:
waves with the same frequency appear repeatedly.
Mu rhythm is highest amplitude in the _______ electrodes.
Central.
If the alpha rhythm is symmetric and synchronous between the left and right occipital electrodes, an EEG recording between O1 and O2 would be?
"Flat."
Occasionally, an unresponsive patient, when stimulated, will have the opposite reaction and the EEG pattern changes to an even slower frequency activity. This is called a ????????
"paradoxical arousal response"
An example of "spike-equivalent" potential. Although this discharge with duration of 155 ms is "sharp wave" by definition, steep descending phase of the wave form is considered to be equivalent to what?
"spike" discharge (an example of "spike-equivalent" potential is enlarged
In an epileptic seizure, there are periods of a sustained depolarization, which cause a train of action potentials followed by a repolarization and hyperpolarization phase. The train of action potentials constitutes the
"spike" phase, and the repolarization and hyperpolarization constitute the "wave" phase
Some sharp discharges show a waveform having a steep declining phase, which are considered to be:
"spike-equivalent" potentials, and have equal clinical significance as spike discharge
Sharp wave
*A transient, usually negative in polarity but can be positive *duration of greater than 70 msec but less than 200 msec. *Voltage is variable but usually is high. *Morphology is sharply pointed.
EEG rhythms
delta, theta, alpha, beta, gamma
Persistent and totally asynchronous activities including sleep spindles have been noted in patients with Aicardi's syndrome, Clinically, the Aicardi's syndrome is characterized by flexion spasms (infantile spasm), chorioretinal abnormalities, and agenesis of corpus callosum, seen solely in girls. What is another example?
Another example of asynchronous sleep patterns (spindle, vertex sharp waves, and K complex) may be seen in patients with obstructive hydrocephalus
In reality, the O1-O2 derivation often shows prominent alpha, even larger in amplitude than that from either O1 or O2 alone, indicating that the alpha rhythm from O1 and O2 is ???
Asymmetric and asynchronous
A number of disorders can be associated with asymmetry, either by interfering with normal cortical function or by increasing the separation between brain and scalp electrodes. Space-occupying lesions such as tumors, hematomas, CSF collections, and unilateral scalp edema are common causes of background asymmetry. Infectious processes, trauma, and infarction may also result in asymmetry.
Asymmetry of the background rhythms with decreased alpha activity on the left compared to the right following a left thalamic infarction
Infantile Spasms (West Syndrome)
Babies with generalized seizures, flexion of back, neck *EEG shows hypsarrhythmia* tx:*ACTH*, vigabetrin,* oral steroids*, benzos or valporate
With an ipsilateral ear reference recording, T3 and T4 amplitudes are erroneously low because:
Because of a cancelation effect due to the short interelectrode distances between T3 and T4 and their respective ipsilateral ear electrodes
Frontocentral alpha activity will show lower amplitude on a bipolar than a referential recording because:
Because of the cancelation effect from electrodes having similar activities, such as between Fp1 and F3.
Bursts consist of ?
Bursts consist of theta and delta activity admixed with low voltage faster activity and rare epileptiform discharges.
What is serial rhythmic (or monomorphic) or intermittent rhythmic delta activity (IRDA)?
Intermittent rhythmic delta activity consists of a series of slow waves having similar wave form, amplitude, and frequency.
A transient is defined by the following features except? -A single wave -It appears and disappears suddenly - Is clearly distinguishable from the ongoing EEG - is always abnormal
Is always abnormal (false).
SIRPIDs (stimulus-induced rhythmic periodic or ictal discharges) are:??
It is not uncommon that diffuse delta/theta slow EEG in obtunded or stuporous patients reveals rhythmic paroxysmal discharges consisting of spike-wave or triphasic waves resembling electrographic ictal (seizure)-like events by external stimulus or spontaneous self-arousal.
The acceptable amplitude asymmetry (difference) of alpha rhythm to be considered normal is:
Less than 50 percent. (ch. 7, page 108)
Faster frequency activity has _____________amplitude.
Lower amplitude.
FIRDA, or frontally predominant RDA is an example of:
MONOMORPHIC delta activity (p. 87)
Wickets
appearance 6-11 Hz usually short runs but can also be a single sharp transient archlike or mu-like, sharp, monophasic symmetric up-slope and down-slope awake and light sleep temporal, usually bilateral and independent arises out of an ongoing rhythm in the background no after-going slow wave clinical significance normal variant predominate in adults older than 30 years related topics: RMTTD
Which filter setting will record the greatest amplitude of a 0.4 Hz wave? a) 5 Hz. b) 0.1 Hz c) 1 Hz. d) 0.3 Hz
b) 0.1 Hz. the slower the LFF setting (or the longer the time constant) , the more voltage of the slow frequencies will be recorded.
Which one of the following frequencies is most attenuated by a low filter of 5 Hz? a) 5 Hz. b) 1 Hz. c) 0.1 Hz. d) 10 Hz.
b) 5 Hz
When the patient is comatose or unresponsive, it is also important to obtain a part of the EEG during a period when the patient is alerted with external or noxious stimuli such as calling the patient's name or pinching the toes or fingernail. This examines any reactive EEG changes to external stimulation. Generally, a reactive EEG suggests a __________ prognosis than a nonreactive EEG.
better
A focal lesion in one hemisphere that involves the optic tracts can cause failure of the normal attenuation of the alpha rhythm on that side with eye opening, due to
blocking of the visual input to the occipital lobe.
Mu rhythm can be attenuated by:
contralateral movement of the arm
Which one of the following frequencies is most attenuated by a low filter of 0.1 Hz? a) 0.2 Hz. b) 2 Hz. c) 0.5 Hz. d) 3 Hz
d) 3 Hz. The faster the slow activity, the more it will be attenuated by a LFF.
Alpha rhythms of unusually large amplitude or exhibiting frontal dominance may be associated with mental retardation and some types of epilepsy. Large amplitude and dominant frontal alpha rhythm may also be recorded in some coma and anesthesia states. In summary, frontal alpha rhythms of moderate amplitude are common in healthy relaxed subjects with closed eyes, but very large frontal alpha is associated with
disease or anesthesia.
Mu rhythm
emanates from premotor/motor regions and are influenced by basal ganglia and sensorimotor function.
If there is a reactive EEG change, it usually consists of what kind of frequency????
faster frequency activity than that before stimulated.
The mu rhythm is present when the body is at rest, but the rhythm is "suppressed" or "blocked" when the person performs a motor action, or, after practice, when the person views another or visualizes a motor action. This "suppression" is also referred to as "desynchronization," which is a term that has been questioned because the EEG does not "desynchronize," but merely
increases synchronization of slower, or synchronization of faster, frequencies
Hypsarrhythmia in an 18-month-old microcephalic boy with infantile spasms. The evidence of multifocal and scattered spikes are better visualized by eliminating slow waves using a shorter time constant (0.003 second) or lower filter setting of 5 Hz. A LFF of 5 Hz results in
less distortion of slow signals. The low frequency filter is used to attenuate or reduce signals below the cutoff frequency, which is also measured in Hz. The amplitude is changed, not the frequency.
If the appearance of waves is sporadic or a series of waves is irregular, the frequency must be determined by:
measuring the duration, which can be converted to the frequency.
When there is an asymmetry in slow waves, the side with slower frequency is?
more abnormal irrespective of the amplitude difference.
Mu rhythm is normal, found in the central derivations (C3/C4) over the motor strip (Figure 2-13). It may be unilateral or bilateral; if bilateral it may be synchronous or asynchronous. Mu is sometimes more evident during drowsiness and when the eyes are open. It is considered to be related to beta activity, possibly a subharmonic. Mu attenuates with?
movement of the opposite upper limb (e.g., making a fist), or even thinking about such an action. It is often prominent over the site of a craniotomy. The importance of mu lies mainly in its recognition as a normal finding.
Out phase signals
output signal will have higher amplitude since they are opposite
in phase signals
output signal will have lower amplitude since they are similar.
Spike discharge
pattern produced by rapid depolarization and repolarization
Mu rhythm is blocked by
real or imagined contralateral motor activity. The mu rhythm frequency band is defined by activity falling between 8 and 13 Hz and recorded by scalp electrodes over the sensorimotor cortex during waking neural activity. The mu rhythm band is posited to reflect the conductance of synchronized activity in large groupings of pyramidal neurons in the brain's motor cortex
Depression of amplitude noted in a bipolar derivation, especially if only in one channel, must be confirmed by a
referential recording
Interictal Epileptiform Dischargers (IEDs), which consists of spike waves and sharp waves, in human electroencephalogram (EEG) are characteristic
signatures of epilepsy. Also called transients. Spikes and sharp waves are defined by their DURATION.
In the rare case when alpha blocking occurs in only one hemisphere, the abnormal side is the one in which
the alpha does not attenuate. This is referred to as the "Bancaud's phenomenon."
The commonly known reactive EEG change is "alpha blocking" or "alpha attenuation" in which the alpha rhythm is best developed during ?????.
the eyes-closed, awake, and relaxed state. Decreases or disappears when the eyes are opened. Asking the patient to open and close his/her eyes a few times at the beginning of the EEG recording is a routine procedure.
If there is an AMPLITUDE ASYMMETRY of the basic background activity,
the side of the LOWER amplitude is usually Abnormal. However, the amplitude asymmetry of alpha rhythm less than 50% is still considered to be normal.
If there is a frequency difference in the basic background activity,
the side with SLOWER frequency is abnormal.
If there is a difference in the amount, abundance, or incidence of BASIC BACKGROUND activity,
the side with decreased background activity is usually abnormal.
