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Normal EEG WAVES

D KALPANA

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HOW TO ANALYSE AN

EEGAGE

STATE OF THE PATIENT

AWAKE

DROWSY

SLEEP

SEDATED

DELIRIOUS

STUPOR OR

COMA

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FACTORS TO BE

ANALYSEDBACKGROUND ACTIVITY

THE FREQUENCY

AMPLITUDE

SYMMETRY

SYNCHRONY

REPONSE TO EYE OPENING, MENTALARITHMETIC, ALERTING SOUND ETC

TRANSIENTS

RESPONSE TO ACTIVATION PROCEDURES

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NOMENCLATUREALPHA

BETA

THETA

DELTA

GAMMA

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BASIC EEG RHYTHMSALPHA 8-13 HZ

BETA - > 14 HZ

THETA 4-7 HZ

DELTA - < 4 HZ

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ALPHA RHYTHMNormal background rhythm in the posterior

head region

8-13 hz20-50 uv

In normal adult in the relaxed state with eyesclosed

Fairly symmetrical and synchronous

Symmetry same amplitude

Normally higher amplitude in right hemisphere

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ALPHA RHYTHM -

continuedSynchrony the frequency should be the

same between hemispheres

A difference of 1hz or more is significantOften the slower frequency is on the abnormal

side

Alpha drop out decrease in amplitude of

alpha during drowsiness

Spontaneous modulations present.

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ALPHA BLOCKINGAttenuation of alpha rhythm in response to

alerting stimuli

Eye openingMental arithmetic

Loud sound

Lack of attenuation to alerting response is signof abnormality.

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http://g/Atlas-figs/pdr-maturation-2a.jpg

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MATURATION OF

BACKGROUND RHYTHM

http://g/Atlas-figs/pdr-maturation-2a.jpghttp://g/Atlas-figs/pdr-maturation-2a.jpghttp://g/Atlas-figs/pdr-maturation-2a.jpg

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Beta rhythmFrequency of over 13 Hz; if >30-35 Hz gammaactivity or exceedingly fast activity by Gibbs.

Average voltage is 10-20 microvolts

Two main types in adults:

The precentral type: predominantly over theanterior and central regions; related to the

functions of the sensorimotor cortex.

The generalized beta activity: induced orenhanced by drugs; may attain amplitude over25 microvolts

Often enhanced during drowsiness or when

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Beta rhythmMostly seen in the anterior leads

The rhythm of the alert brain

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Theta wave

rhythmic, 4-7 Hz

Drowsy, sleep

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Delta wave

slow, < 3.5 Hz

in adults

normal sleep rhythm stage 3 & 4

In stupor and coma

Encephalitis and postictal state

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Different types of brain waves innormal EEG

Rhythm Frequency

(Hz)

Amplitude

(uV)

Recording

& Location

Alpha() 8 13 50 100 Adults, rest, eyes closed.Occipital region

Beta() 14 - 30 20 Adult, mental activityFrontal region

Theta() 5 7 Above 50 Children, drowsy adult,emotional distress

Occipital

Delta() 2 4 Above 50 Children in sleep

D T A B

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Factor influencing EEG

Age

Infancy theta, delta wave

Child alpha formation.

Adult all four waves.

Level of consciousness (sleep)

Hypocapnia(hyperventilation) slow & highamplitude waves.

Hypoglycemia

Hypothermia

Slow waves

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Changes in brain waves during

different stages of sleep & wakefulness

Ch i b i d i

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Changes in brain waves duringdifferent stages of sleep &

wakefulness

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Sleep Spindle

K - complex

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Thank you