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Normal and Sleep EEGDr Archana KushwahChoithram Hospital & Research Centre ,Indore
Guide Dr Vinod RaiChoithram Hospital & Research Centre ,Indore
Normal & Sleep EEG Introduction Definition Descriptors of EEG activity
Normal EEG (Wakeful adult)
Normal Sleep EEG Normal EEG (Extremes of age)
Activation procedures Artifacts Benign or normal EEG variants
Hans Berger (1873–1941) recorded the first human EEG in 1924
Brief History● Vladimirovich (1912)● first animal EEG study (dog)● Cybulski (1914)● first EEG recordings of induced seizures● Berger (1924)● first human EEG recordings● 'invented' the term electroencephalogram (EEG)● American EEG Society formed in 1947● Aserinsky & Kleitman (1953)● first EEG recordings of REM sleep
INTRODUCTION (What, Where, How) What
Electrical potential generated by summation of cortical nerve cell(Pyramidal cell) EPSP & IPSP: Not AP
INTRODUCTION (What, Where, How)
Where Thalamic pacemaker cells in nucleus reticularis
Thalamocortical neurons stimulated
excitatory impulses to cortex.
INTRODUCTION (What, Where, How) How
EEG is difference in voltage between 2 recording electrodes plotted over time.
10-20 10-10
Definition of normal EEG Normal EEG
Absence of abnormal components No criteria for normal patterns Requires recognition of normal patterns at
different ages and level of alertness Normal EEG does not always mean normal brain function. Abnormal EEG does not always mean abnormal brain
function.
Descriptors of EEG Morphology Repetition Frequency Amplitude
Distribution Phase relation Timing Persistence Reactivity
Descriptors : 1.Morphology
Wave : difference of electrical potential between two recording electrodes
Wave form : describes the shape of wave.Transient &/or paroxysm: stands out against the background
Descriptors : 2.Repitition Rhythmic Semi rhythmic Irregular polymorphic
Descriptors : 3.Frequency Number of times a wave recurs in 1 sec.Slow waves < 8 Hz. Fast waves > 13 Hz.
Total vertical distance of a wave. Measured in not in mm. Low< 20 :medium 20-50:high >50 Changing the montage changes the voltage. Amplitude assymetry ~ confirmed by montage change.
Descriptors : 4.Amplitude
Wide spread/ diffuse/ generalised. Lateralized. Focal / localized. Multifocal epileptiform pattern
3 or more anatomically distinct areas generating epileptiform activity. In describing location electrode names should be used.(not head regions / brain areas)
Descriptors : 5.Distribution
Descriptors : 6.Phase relation Timing and polarity of components of
waves in 1 or more channels. In phase (Troughs and peaks occur at same time in different channels) Out of phase (Troughs and peaks donot coincide) Phase reversal (peaks pointing in oppposite direction)
Descriptors :
7.Timing•Synchronous(same time)•Asynchronous •Independent •5millisec and <time can be appreciated by digital instruments.
8.Persistence
•How often a wave or pattern occurs during the recording. •Persistence index •High /moderate/ low•Sporadic / periodic
9.Reactivity •Changes produced by various maneuvers.•Opening or closing eyes•Hyperventilation•Photic stimulus •Sensory stimulus•Changes in level of alertness.•Movement
Normal EEG (wakeful adults) Alpha rhythm Beta rhythm
Mu rhythm Lambda waves
Vertex sharp transients Kappa rhythm
Intermittent posterior theta rhythm Low voltage activity
Alpha rhythm Frequency
8 Hz & Distribution
posterior head region
Reactivity Blocked by eye
opening and other alerting maneuver.
Disappears in drowsiness and sleep
Alpha rhythm(frequency) 8-13 Hz Nearly constant in a given individual throughout
life(decline of 1 or more Hz is abnormal) Frequency in two hemisphere should be same
difference of over 1 Hz is abnormal Hemisphere with lower frequency is abnormal.
Squeak phenomenon Brief increase in frequency after eye closure
followed by rapid deceleration to baseline frequency.
Alpha rhythm (distribution) Greatest amplitude and most persistent
in occipital, posterior temporal and parietal areas.
Alpha frequency activity restricted to FP1and FP2 is eye movement artifact until proven otherwise.
Alpha rhythm (reactivity) Blocked by eye opening, sudden alerting,
attention to visual and other stimuli, mental concentration.
Bancaud phenomenon Unilateral blocking of alpha rhythm indicates
presence of abnormality of non reactive hemisphere.
Paradoxical alpha rhythm Alpha rhythm appears on eye opening and
disappears on eye closure in drowsy patient. Partial alerting response
Alpha rhythm Phase relation
Often not in phase Amplitude
Commonly more on right side Left side should be at least 50% of right. Asymmetry depends on occipital bone
thickness.(not on handedness) Alpha variants
Slow alpha variant ~3.5-6.5 Hz: admixture with normal alpha: blocks as alpha.
Fast alpha variant ~ 16-20Hz: blocks as alpha. Physiological purpose
Possibly integrated with visual system function.
Beta rhythm Frequency
Over 13 Hz Upper beta range ~ gamma
range Distribution and reactivity
Frontal MC Blocked by movement /
intention to move/tactile stimulus (opposite hemisphere)
Widespread Not blocked by any stimulus
Posterior (fast alpha) Accentuates in
Drowsiness and stage 1 sleep. Excess medication (BDZ &
Barbiturate)
Beta rhythm Amplitude
Assymetry ~> 35% is abnormal
Breach rhythm Localised increase in
beta activity in skull defect areas.
Physiological significance Possibly integrated
with S/M function of the brain.
Almost always a good prognostic sign.
Mu rhythm Wicket/comb/arceau rhythm <5% EEG: young adults 7-11Hz For few seconds in central or
centroparietal area(difference from alpha by blocking)
At different times on both sides
Intermittent & asymmetrical : persistent asymmetry on same side is abnormal
Facilitated when scanning visual images.
Blocked by ~ voluntary/ reflex/passive movement/intention to move /tactile stimuli.
Physiological significance Somatosensory process associated
with movement.
Lambda rhythm Saw tooth shaped Positive polarity Occipital Appears on looking
at images containing visual details.
100-250 millisecond duration,< 50microvolt
Resembles POST in shape and distribution.
Accompanied by eye movement & eye blink artifact. Neither presence nor absence is abnormal
Asymmetry is abnormal
Vertex sharp transients (V waves)
Single, negative polarity Maximal over vertex
extends to F,P,T area. Common in normal sleep Wakeful adults
Sudden loud noise/startle/percussions of hands or feet.
>2 times /sec, bilateral synchronous
Kappa rhythm
Bursts of very low amplitude
of alpha or theta
frequency
In temporal lobe
engaged in mental activity.
Normal posterior theta rhythm
Slow alpha variant
Rhythmic slow waves of
4-5 Hz
Blocking & distribution
same as alpha.
Low voltage EEG
No activity over 20 microV
More common in advancing age / tense subjects.
< 10microV abnormal
<2 microV electrocerebral inactivity(brain
dead)
Normal sleep EEG (adults) Elements of normal sleep activity
Slow waves Positive occipital sharp transients Vertex sharp transients Sleep spindles K complexes
Sleep stages Sleep cycle
Slow waves More prominent posteriorly. Less persistent, more asynchronous, low
amplitude, fast frequency in light sleep than deep.
POSTS
Triangular waves in occipital area
4-6Hz. Mono /bi phasic Lambdoid
waves (Shape & distribution)
Prominent lambda waves are associted with more POSTS & photic driving responses.
Sleep spindles 12-14Hz Duration >0.5 sec Maximum over
central After 2 years
simultaneous and symmetrical
K COMPLEXResembles v wave in distribution , reactivity and polarity>0.5 secLess sharply contoured
Stages of sleepStage W
• Slowing • Predominance of alpha• Prominent beta in drug
induced• SEM (first EEG sign of
drowsiness)
Stage 1
• Disappearance of alpha(30 sec Epoch ~ < 50% alpha)
• Paradoxical alpha• Slow waves
Sleep stage 2 Sleep spindles K complexes Slow waves
continue POSTS often
persists V wave often
persist
Sleep stage 3 & 4Stage 3
• 20-50% of 30 sec Epoch contains • Waves of 2Hz or < • Waves of <75 microV• In C3-A1 or C4-A2
• K complexes / sleep spindles/POSTs
Stage 4
• >50%• K complexes blend with
slow waves• Spindles & POSTs rare• After 55 yr~ St 3& 4
rare(only amplitude criteria apllied)
REM sleep > 50% of a 30 sec
Epoch contains Low voltage EEG Prominent theta
wave Rapid eye movt. Reduced muscle
tone Resemble stage 1
but no v wave Saw tooth wave Alpha frequency
~1-2 Hz Appearance of
REM in routine EEG is pathological.
Sleep cycle
Each cycle~ all stages NREM & REM: 4-7 cycles /sleep 1st cycle shortest: later 80-120 min. :REM sleep ~ appears 70-90 min after onset
of sleep. Young adults: 30-50% stage 2; 20-40% stage 3&4: 5-10% stage 1 REM sleep: 25% in young adults & 20% in 5th decade.
EEG of elderly(>60years) Alpha rhythm
Frequency, persistence, reactivity &voltage Beta activity
More prominent : incidence & amplitude Sporadic general slow waves
More common than young adults. Intermittent temporal slow waves
Especially on lt. side < 1% of waking record should be delta range < 10% in theta range(Arrena et al)
Sleep Fairly prominent slow waves Sleep depth and consolidation reduced(St 3,4) REM sleep to < 20%
EEG of premature age to 19 years Maturation of EEG parallels anatomical &
physiological development of brain EEG of neonate is a function of actual age of
brain Conception age (CA)= gestational age + legal age Always try to record normal active
newborns immediately after feeding(quiet wakefulness)
CA< 29 wksTrace discontinueInterhemispheric synchronyDelta brush pattern
EEG of premature age to 19 years CA~ 29-32 wks
Lowest Interhemispheric synchrony Temporal theta burst(temporal saw tooth wave) Highly useful for estimating CA
EEG of premature age to 19 years CA~ 32-34 wks
Multifocal sharp transients ; abundant delta brush
EEG reactivity starts.
EEG of premature age to 19 years CA ~ 34-37 wks
Frontal sharp transients/ mono rhythmic frontal slowing
Trace alternans(delta brush & multifocal sharp transietns )
Inter hemisheric synchrony Activity Moyene.
CA ~ 38 -42 wks Similar to full term 4 basic pattern
Low voltage irregular (wakeful & active sleep)
Mixed vol (wakeful & transitional sleep)
High vol. slow Trace alternans
EEG of premature age to 19 years Full term to 3 month
Precursor of alpha rhythm~ 3-4 Hz
Sleep spindles appear Asymmetry up to 8 months
; beyond 2 yr asyym. Is abnormal.
Trace alternans / multifocal sharp transient disppear.
Interhemispheric synchrony 100%
Reaction to tactile and auditory +
Lamba waves
EEG of premature age to 19 years
3 months – 1 year Wakefulness~ BGA –
theta & delta range Occipital rhythm
Drowsiness Hypnogogic
hypersynchrony Sleep
Starts to resemble adult Cone / O waves Sleep spindles appears
at 3-6 mnt; assym. up to 8 mnt.
V waves & k complex ~ 3-6 mnt.
EEG of premature age to 19 years 1-19 YEARS
Gradually becomes same as adult Alpha frequency gradually increases. Slow waves more prominent up to 4 years. Posterior slow waves of youth
Most common at 8-14 years Hypnogogic hypersynchrony rare after 12 years SEM appears at 10 years. 14-6 Hz burst more common than adults. POST begin to appear.
Activation procedures Hyperventilation Sleep deprivation Photic stimulation Others
Pattern or video game sensitivity Auditory stimuli Reading Eye opening /closing and mental concentration Tactile stimulation Drugs
Artifacts Physiologic
alBlinking and eye
movementsMuscle artifact
Movement artifact
ECG
Pulse wave artifact
Skin potentialMovements of tongue and oropharyngeal structures
Dental restoration
Non physiologic
al External electrical
interference
Internal electrical malfunctioning of recording system
Benign or normal EEG variants
Rhythmical patterns
RMTD/RTTD
Alpha variants
SREDA
Midline theta rhythm
Frontal arousal rhythm
Benign patterns with epileptiform morphology
14 & 6 Hz positive burst(Ctenoids)
Small sharp spikes(SSS)
6 Hz spike and wave bursts(Phantom)
Wicket spikes
Breach rhythm.
SREDA
Ctenoids
SSS/BETS
Reference Fisch & Spehlmann’s EEG primer: 3rd
edition: Elsevier 2009 Current pratice clinical EEG : 3rd edition :
Pedley: liipincot williamson & wilkin 2003