Electroencephalography (EEG) - Eötvös Loránd...

Electroencephalography (EEG)

Human neocortex – lobes and areas

parietal lobe

frontal lobe

occipital lobe

temporal lobe

Mediansagittal section of human brain

parietal lobe

frontal lobe

corpus callosum

thalamus

amygdala

occipital lobe

temporal lobe hippocampus

Structure of human neocortex - pyramidal neurons

Generation of EEG Piramissejt

sink

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Thalamocortikális EPSP

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EEG waves represent the contributions of summed

synaptic potentials in the apical dendrites of the cortical pyramidal neurons

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Generation of EEG

EEG recording

Different EEG electrodes

The first human EEG - Berger

1920s

Hans Berger

International 10-20 system

Characteristic EEG waves

beta (β)

alpha (α)

theta (θ)

delta (δ)

50 µV

Awake: low-voltage random, fast, > 13 Hz, < 10 µV

Drowsy: 8-13 Hz, 10 -50 µV

Sleep stage 1: 4-8 Hz, 50 µV, theta waves

Sleep stage 2: 12-14 Hz, sleep spindles and K complexes

Deep sleep (sleep stage 3-4): 0-4 Hz, >75 µV

REM sleep: low-voltage random, fast with sawtooth waves

beta (β)

1 s

Main EEG characteristics • synchronisation:

- nearby cortical pyramidal neurons function in synchrony e.g. lack of sensory stimulation in the sensory cortex - EEG waves: amplitude increases, frequency decreases - open -> closed eyes: β -> α waves over the occipital lobe (primary visual center)

• desynchronisation: - nearby cortical pyramidal neurons behave differently:

e.g. sensory stimulation in the sensory cortex

- EEG waves: amplitude decreases, frequency increases, irregular waves - closed -> open eyes: α -> β waves over the occipital lobe (primary visual center)

Normal, awake EEG recorded from an adult

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2

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4

1: small amplitude β activity 2: λ waves in the occipital region, during picture viewing 3: α rhythm (α spindles) in the occipital region, minimal β activity

4: desynchronization due to the opening of the eyes

Sleep cycles

time (h)

NREM: slow-wave sleep (SWS)

REM: rapid eye movements, paradoxical sleep

Normal EEG recorded from an adult during sleep 1

2

3

1: stage 2 of slow-wave sleep with K complex (a) and sleep spindle (b) 2: deep slow-wave sleep (stage 4) with consecutive delta waves (e) 3: REM sleep with artefacts due to eye movements

Normal EEG activity from a 8-month-old child

1: awake, resting state 2: light sleep (drowsiness) 3: asynchronous activity, deep sleep

Recording artefacts

1: blink,

2-EO: opening of the eye,

3-EC: closing the eye, 4-EM: slow eye movements, 5-EM: saccadic eye movements

Recording artefacts II

1-2: muscle movements, 3: ECG artefacts, 4: muscle movement artefacts due to talking

5: muscle movement artefacts due to chewing

Asymmetric hemispheral activity

Synchronizing effects of rhythmic light flashes

1: normal EEG 2-8: 1, 3, 6, 9, 12, 15 and 18 Hz flashes

Generalised grand mal epilepsy

1: tonic phase, 2: clonic phase

Generalised petit mal or “absence”, "spike and wave" epilepsy