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