EEG Teaching Courses
Tamer Belal, MD ,PHD
Lecturer of Neurology
Mansoura University Hospitals
Uses of ambulatory EEG
Evaluation of interictal epileptiform activity
Documentation of seizures of which patients are unaware
Evaluation of response to therapy
Evaluation of nocturnal or sleep-related events
Evaluation of suspected pseudoseizures
Evaluation of syncope
Uses of ambulatory EEG
Normal EEG
waves
Normal EEG waves
Type
Frequency
(Hz)
Location
Normally
Pathologically
Delta
0-4
frontally in adults,
posteriorly in children;
 high amplitude waves
adults slow wave sleep (deep sleep)
in babies
Has been found during some
continuous attention tasks
subcortical lesions
diffuse lesions
Metabolic
encephalopathy
hydrocephalus
deep midline lesions
Theta
4-8
Found in locations not
related to task at hand
young children
drowsiness or arousal in older children
and adults
Associated with inhibition of elicited
responses (has been found to spike in
situations where a person is actively
trying to repress a response or action)
focal subcortical lesions
metabolic
encephalopathy
deep midline disorders
some instances of
hydrocephalus
Alpha
8-13
(5-100uv)
posterior regions of head,
both sides, higher in
amplitude on non-dominant
side. Central sites (c3-c4) at
rest
Relaxed/reflecting
Closing the eyes
Also associated with inhibition control,
seemingly with the purpose of timing
inhibitory activity in different locations
across the brain.
Attenuated by eye opening, attention
and mental effort (Alpha block)
Alpha Coma
(unresponsive)
Paradoxical alpha
Interside differences˃50%
(lt)
Unilateral failure of the
alpha rhythm to attenuate
reflects an ipsilateral
abnormality (Bancaud’s
phenomenon
Normal EEG waves
Type
Frequency
(Hz)
Location
Normally
Pathologically
Beta
˃13-30
˂35uv
both sides, symmetrical
distribution, most evident
frontally; low amplitude
waves
alert/working
active, busy or anxious thinking,
active concentration
•Benzodiazepines
Gamma
30-100+
Somatosensory cortex
Displays during cross-modal
sensory processing (perception
that combines two different
senses, such as sound and sight)
Also is shown during short term
memory matching of recognized
objects, sounds, or tactile
sensations
A decrease in gamma band
activity may be associated with
cognitive decline, especially
when related the theta band;
however, this has not been
proven for use as a clinical
diagnostic measurement yet
Mu
8-13
Sensorimotor cortex
Cz and Pz
Shows rest state motor neurons
During wakefulness
Attenuated by contraction of
contralateral muscles
When persistent, unreactive, and
associated with focal slowing, mu
like frequencies are abnormal
Mu suppression could indicate
that motor mirror neurons are
working. Deficits in Mu
suppression, and thus in mirror
neurons, might play a role in
autism
Normal EEG waves
Electrodes
Recording System
Electrodes Board
Electrodes
Selector
Switches
Filters
Amplifier
Chart Drive
Power supply
Recording System
Sleep and EEG
EEG and states of
Arousal
The 5 principles of localization
Rule
1
Widely placed electrodes record larger voltages than closely placed
electrodes
Rule
2
The potential recorded from the pair having one electrode at F will be
greater than the potential recorded from the pair having neither
electrodes at F
Rule
3
The further away the dipole is from the surface of the scalp the smaller
will be the potential observed at the surface, inter-electrode distance
being constant
Rule
4
Phase reversal is really an instrumental one and no true phase reversal.
The reversal results from the fact that the shared electrodes goes to
opposing inputs and hence causes the opposite deflection to occur
Rule
5
If two Electrodes are equidistant from the focus, no voltage will be
recorded between them (Cancellation)
The 5 principles of localization
Widely placed electrodes record larger voltages than
closely placed electrodes
The potential recorded from the pair having one electrode
at F will be greater than the potential recorded from the
pair having neither electrodes at F
The further away the dipole is from the surface of the
scalp the smaller will be the potential observed at the
surface, inter-electrode distance being constant
Phase reversal is really an instrumental one and no true
phase reversal. The reversal results from the fact that the
shared electrodes goes to opposing inputs and hence causes
the opposite deflection to occur
If two Electrodes are equidistant from the focus, no voltage
will be recorded between them (Cancellation)
The 5 principles of localization
Commonly seen localization patterns
A Phase reversal observed in a line of referentially connected electrodes
is a true phase reversal . The longer the deflection associated with a
particular focus of activity, the closer is the electrode to the focus
Contamination results from a significantly active F included in the
reference electrode.
Commonly seen localization patterns
(A) Bipolar montage demonstrating phase reversal and (B) referential
montage demonstrating absolute voltage.
Commonly seen localization patterns
EEG demonstrating bipolar (A) and reference (B) montages to illustrate a
left anterior temporal sharp wave.
Commonly seen localization patterns
The rules governing polarity and convention relative to “pen”deflection.
When input 1 is negative the deflection is up.
EEG Reading
Both the background activity and the changes that appear in the features
of the tracing are described in the following terms
Frequency: fast, slow, monomorphic, polymorphic or periodic
Amplitude :low ˂20uv, Medium 20-5-uv, high˃50uv
Attenuation and blocking, suppression , paroxysmal
Wave shape (morphology) : transients (sharp, spike) or
complex, monomorphic , polymorphic
Symmetry (synchrony)
Location : focal , generalized or lateralized
Continuity : continuous or intermittent
Reactivity
Writing the EEG report
Two parts
1- Actual description f the EEG findings and their interpretation
2- Clinical correlation that render the report meaningful
Brief history of the clinical findings today
Mention what the referring physician hope to find out
Descriptive details regarding the testing situation
Describe the state of the patient
Describe the EEG ( just descriptive)
Impression : normal or abnormal and define abnormality
Attempt to correlate the EEG with clinical picture
Suggest further study if needed
Writing the EEG report
The EEG was recorded with the standard 10-20 system of electrode placement.
The patient was awake and cooperative.
EEG Report : Background activity comprises of alpha activity 9-10 c/s, which is
symmetrical in the occipital leads and spreading anteriorly interspersed with fast
beta activity. No paroxysmal activity seen. Hyperventilation and photic stimulation
is non-contributory.
IMPRESSION: Normal record. No epileptiform activity seen. Clinical correlation
advised.
Note: A normal EEG does not rule out the diagnosis of epilepsy, as epileptiform
discharges may be paroxysmal.
Abnormal EEG Patterns
Abnormality of background rhythm
Abnormal sleep patterns
Abnormal slow activity:
Generalized intermittent slow activity
Focal and lateralized intermittent slow activity
Persistent slow activity
Paroxysmal epileptogenic abnormalities
Inter-ictal epileptiform discharges( focal, generalized)
Ictal
Secondary bilateral synchrony
Epileptiform patterns of doubtful significance
Abnormal periodic paroxysmal patterns
Generalized periodic paroxysmal patterns
SSPE,CJD,Herpes S E, suppression patterns, Triphasic waves
Lateralized periodic paroxysmal patterns
PLEDS,BPLEDS
The Normal EEG Patterns
Alpha rythm
Alpha frequency
Normal 10-Hz alpha rhythm “blocked” by eye opening and returning on eye
closure. Note the faster frequency immediately on eye closure (“squeak”).
The Normal EEG Patterns
Note the prominent left central mu rhythm during eye opening (Mu rhythm)
The Normal EEG Patterns
Breach rhythm in the right temporal region (maximal at T4) following craniotomy
for temporal lobectomy
The Normal EEG Patterns
Normal frontocentral theta rhythm in an 18-year-old patient while awake.
The Normal EEG Patterns
Bi-occipital lambda waves in a 28-year-old patient with dizziness.
Notice the frequent “scanning” eye movement artifact in the F7 and T8 derivations.
The Normal EEG Patterns
Intermittent left mid-temporal delta during transition to drowsiness in a normal
84-year-old patient evaluated for syncope
The Normal EEG Patterns
NORMAL SLEEP ARCHITECTURE
POSTS appearing in the lower three channels in a bipolar circle montage
demonstrating positive polarity in the occipital region during sleep.
Notice the surface negative vertex waves maximal at Cz
The Normal EEG Patterns
NORMAL SLEEP ARCHITECTURE
Stage 2 sleep with prominent sleep spindles and POSTs
The Normal EEG Patterns
NORMAL SLEEP ARCHITECTURE
Slow-wave sleep. Note the intermittent POSTs and sleep spindles against the
continuous delta background
The Normal EEG Patterns
NORMAL SLEEP ARCHITECTURE
REM sleep with rapid eye movements associated with lateral rectus spikes is noted
at the F7 and F8 derivations
The Normal EEG Patterns
ACTIVATION PROCEDURES
Normal build-up during hyperventilation
The Normal EEG Patterns
ACTIVATION PROCEDURES
Normal 10-Hz alpha rhythm “blocked” by eye opening and returning on eye
closure. Note the faster frequency immediately on eye closure (“squeak”).
The Normal EEG Patterns
BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCE
Rhythmic temporal theta bursts of drowsiness.
Note the sharply contoured morphology.
The Normal EEG Patterns
BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCE
Central theta (maximal at Cz) seen during the awake state in a 35-year-old patient
with migraine headaches
The Normal EEG Patterns
BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCE
A 6-Hz (phantom) spike-wave burst with frontal predominance in the 5th second
of this EEG in an awake patient with temporal lobe epilepsy.
The Normal EEG Patterns
BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCE
Fourteen- and 6-Hz positive bursts maximal in the T6 electrode derivation in a
linked-ears reference montage. Note the downward deflection and prominent 14Hz frequency
The Normal EEG Patterns
BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCE
A right benign Epileptiform transients of sleep (BETS) in the temporal region
during stage 2 sleep. Note the higher amplitude in the T1 and T2 channel with a
longer interelectrode distance
The Normal EEG Patterns
BENIGN VARIANTS OF UNCERTAIN SIGNIFICANCE
Wicket waves maximal at T3 and T4
Normal
EEG
Variants
Normal EEG Variants
Refer to waves that are rare or unusual but not generally
abnormal. They may be unusual in shape or in distribution.
They can include
wave mixtures that can appear unusual and can
confuse the casual reader (for example, wave
harmonics)
Artifacts or electrical disturbances from
structures that are not in or part of the brain
and do not affect the brain or its function but
appear in the EEG tracing
Normal EEG Variants
Odd-Looking Waveforms
Psychomotor variant (rhythmic harmonic theta)
Mu (rhythm en arceau or wicket rhythm, arciform rhythm )
14- and 6-Hz waves
Small sharp spikes of sleep (SSS) , benign epileptiform transients
of sleep (BETS). posterior occipital transients of sleep POSTS
6-Hz spike and wave (phantom spike and wave)
Wicket spikes
Subclinical rhythmic EEG discharges in adults
Rhythmic midline theta
Normal EEG Variants
Odd-Looking Waveforms
Psychomotor variant (rhythmic harmonic theta)
Asymmetrical runs of theta or delta activity primarily in the
mid-temporal regions, lasting for a few seconds or as long as 3045
occurs in 0.5% to 2.0% of selected normal adults and consists
of bursts or runs of 5- to 7-Hz theta waves that may appear
sharp, flat, or notched in appearance
It starts suddenly on 1 side and lasts for several seconds before
terminating suddenly. This behavior resembles a seizure
discharge, hence the name "psychomotor variant."
Generally considered benign, this waveform does not correlate
with seizure disorder. It is best seen on a prolonged EEG and
tends to be more common in children and young people
Normal EEG Variants
Odd-Looking Waveforms
Psychomotor variant (rhythmic harmonic theta)
Rhythmic temporal theta bursts of drowsiness. Note the sharply
contoured morphology.
Normal EEG Variants
Odd-Looking Waveforms
Mu (rhythm en arceau or wicket rhythm, arciform rhythm )
This waveform is recognized easily and has no pathological
significance. The naive may not recognize it and assume it to be
abnormal
The mu waveform occurs in the central regions in the awake
patient. It is seen best if a bone defect underlies the electrodes
It can be markedly asymmetrical
Often in the alpha range frequency, it has rounded positive
aspects on 1 side and sharpened negative aspects on the other
It is not blocked by eye opening
It becomes obvious when the alpha disappears (ie, alpha
blocking).
Associated with fast activity, mu has a frequency about half
that of fast activity.
The most classical feature of mu waveform is that it blocks
with motor activity of the contralateral body (or the thought of
such movement).
Normal EEG Variants
Odd-Looking Waveforms
14- and 6-Hz waves
The 2 frequencies are intimately intertwined and the complexes occur
in bursts.
They generally are thought to be clinically insignificant.
They occur in healthy children and adolescents. Some claim that they
are best seen in referential recordings during sleep
Small sharp spikes of sleep (SSS)
This waveform also is known as benign epileptiform transients of sleep
(BETS).
These sharp, small waves occur on 1 or both sides (often
asynchronously), especially in the temporal and frontal regions.
Rarely seen in children, they are seen most often in adults and the
elderly
They can occur in epileptic patients but often are seen in healthy
individuals. They can be regarded as a probable normal variant
Normal EEG Variants
Odd-Looking Waveforms
6-Hz spike and wave (phantom spike and wave)
These occur as bursts of miniature spike and wave complexes or runs of
such complexes at 6 Hz rather than the usual 2-4 Hz.
Their significance is debated, but generally those occurring in the
posterior head regions are regarded as benign
Seen at all ages (but especially in adults), they often are confused with
14- and 6-Hz waves and may merge into them
The anterior variety are regarded by some as consistent with epilepsy,
but further studies are needed to confirm this
Wicket spikes
•Almost exclusively in adults
•Like wicket rhythm, (rounded aspects to 1 side and sharp points to the
other, giving the appearance of spikes or sharp waves
•distinguished by their morphology and at times by their defined
background rhythms, which are harmonizing.
•Can be seen either in wakefulness or sleep in the anterior or temporal
head regions.
Normal EEG Variants
Odd-Looking Waveforms
Subclinical rhythmic EEG discharges in adults
SREDA consists of theta rhythm occurring in a widespread manner,
maximal over the parietal and posterior temporal regions, and lasting
for a few seconds to a minute without clinical signs or symptoms.
It is described as "not evolving" and appears quite stable for its
duration.
Mechanism of SREDA is not understood, represent a benign EEG
phenomenon that distinguished from seizure discharges
Another unusual variant (delta rhythm as well as notched waveforms
with a frontal distribution and a more prolonged duration that even
includes sleep(FRIDA)
Rhythmic midline theta
•Rhythm maximal at the midline, most prominently at Cz
•It has a frequency of 5-7 Hz and typically has an arciform, spiky, mu like
appearance
•Waxes and wanes, can appear during wakefulness or drowsiness, and is
usually reactive to eye opening or limb movement
Normal EEG Variants
Artifacts
Forehead, jaw, and eyelid muscle movements homotor variant
(rhythmic harmonic theta)
Tongue and eyes have their own dipole electric chargeu (rhythm
en arceau or wicket rhythm)
Sweating produces electrical disturbances by shorting electrode
pairs.
Other sources of artifacts include ambient electrical waves from
respirators, intravenous pump machines, televisions, and other
electrical equipment.
Normal EEG Variants
Artifacts
Many are recognized by their characteristic appearance on the
tracing, but others are identified by direct inspection and
reported by the technologist or identified on the video tracing in
video-EEG recording.
Artifacts show great variation because of their protean origin.
They may be single waves or recurrent waves (eg, intravenous
infusion running), while others are prolonged disturbances (eg,
sweating).
Artifact produced by tongue movement
EEG artifact of eye blinking.
Example of EEG chewing artifact
Normal EEG Variants
Artifacts
The following can be regarded as clinically insignificant
Chewing produces spurious spike and wave runs in the frontal
and temporal regions from the temporalis muscles
Sweating produces very slow waves, because the salt solution
shorts out pairs of adjacent electrodes
Eye movements occur with blinking and result from the
electrical charge of the eye itself (see image below). They are
frontal. Nystagmus also produces artifactual waves
ECG and pulse motion produce unusual waveforms. ECG
produces small spikes that are recurrent and are especially
evident in the monopolar montages.
Normal EEG Variants
Artifacts
The following can be regarded as clinically insignificant
Tremor and movement of the head or body may cause
electrodes to move
Electrode pops or movements can produce sudden, recurrent,
or continuous electrical waves
Electrical fields result from electrical devices and televisions.
ICU special waveforms may result from respirator-induced
movements, intravenous drips and drip pumps, electrical fields,
or cautery in the operating room or emergency department.
Normal EEG Variants
Harmonics
EEG is a complex summation of many frequencies
Different frequencies sometimes add to or cancel each other,
creating odd waveforms or fluctuations of waveforms
Pseudospikes or pseudoslow waves may be seen with
intermixing of waves.
Many fascinating patterns have been generated by mixing
artificially created computer-generated frequencies.
These waveforms have the significance of the basic waveforms
that underlie the patterns.
Central theta (maximal at Cz) seen during the awake state in a 35-yearold patient with migraine headaches
A 6-Hz (phantom) spike-wave burst with frontal predominance in the 5th
second of this EEG in an awake patient with temporal lobe epilepsy.
Fourteen- and 6-Hz positive bursts maximal in the T6 electrode
derivation in a linked-ears reference montage. Note the downward
deflection and prominent 14-Hz frequency.
A right benign epileptiform transients of sleep (BETS) in the temporal
region during stage 2 sleep. Note the higher amplitude in the T1 and
T2 channel with a longer interelectrode distance.
Wicket waves maximal at T3 and T4.
SREDA in a 73-year-old patient during hyperventilation (HV). No clinical
signs were present.
Thank you