1. Electroencephalography
doc. MUDr. Valja Kellerová, DrSc.
Department of Neurology

2. Principle of EEG:
EEG examines the spontaneous electrical activity of the brain by means of scalp electrodes
recording procedure: amplification
recording (20 minutes at least)
storage (on CD, DVD,
NAS, cloud …)

3. Electrode placement – the „ten-twenty“ electrode system

4. Principle of registration
EEG curve is registered/recalculated as the difference of electric potentials between two electrodes (varying in the course of time)
derivation = recording from a pair of electrodes (two electrodes are connected to a single amplifier, to one EEG channel)
bipolar
monopolar

5. Montages montage = a particular electrode arrangement,
a number of different derivations is diplayed simultaneously
commonly used and preset montages:
longitudinal
transverse
( referential )

6. EEG reading
Morphology
Amplitude
Frequency

7. EEG reading: morphology (wave shape)
sharp waves
spikes = epileptiform patterns,
spike-and-wave complexes… they accompany epilepsy

8. EEG reading: amplitude
voltage in microvolts
a peak-to-peak measurement
compared with the calibration signal
commonly μV (in normal EEG)
amplitude changes may be pathological

9. EEG reading: frequency
the rhythmic EEG activity is classified as:
delta - less than 4 Hz
theta – 4 to 8 Hz
alpha – 8 to 13 Hz
beta – more than 13 Hz

10. Normal rhythms Alpha rhythm sinusoidal waves (8-13 Hz)
maximal over the posterior head region (occipitally)
occurs during wakefulness and relaxation
best seen with the patient’s eyes closed
blocked or attenuated with eye opening

11. Normal rhythms Beta rhythm Delta rhythm Theta rhythm is not prominent
has low amplitude
is best seen frontally
not affected by eye opening
Theta rhythm
a small amount, of low amplitude, frontally
accompanies drowsiness
Delta rhythm
is normal during deep sleep
is normal in childhood
is abnormal in the other cases

12. The normal EEG: awake EEG in adults
typical normal EEG:
alpha rhythm
the posterior dominant rhythm
blocked with eyes opening
Frontally beta and theta low amplitude activity

13. The normal EEG: awake EEG in adults
low voltage EEG („atypical flat EEG“)
a variety of normal finding
10% of normal healthy adults
no activity over 20 μV
various frequencies may be present
alpha rhythm may be absent

14. The normal EEG during drowsiness and NREM sleep
Drowsiness - somnolence
disappearance of the alpha rhythm
low voltage beta activity or flat recording
low voltage theta (5-6 Hz)
3-4 Hz (moderate amplitude)
paradoxical reaction to eye opening (alpha rhythm appears)

15. The normal EEG: EEG during drowsiness and sleep - NREM sleep
Sleep stage 2:
slow waves 3-4 Hz continue
sleep spindles
( Hz)
and K complexes (reaction to stimuli)

16. The normal EEG: EEG during drowsiness and sleep - NREM sleep
Sleep stage 3:
slow waves of 2 Hz or less, of high amplitude (20-50% of the recording time)
Sleep stage 4:
slow activity of about 1 Hz (over 50%)

17. The normal EEG: EEG during drowsiness and sleep - REM sleep
REM sleep (paradoxical sleep):
associated with dreaming
asynchronous low voltage waves of mixed frequency
may resemble the pattern of stage 1

18. Polysomnography
For reliable determination of REM stage polysomnography is necessary with recording also:
rapid eye movements
heart rate and breathing
EMG of the mental muscles (postural) – tonic activity disappears in the REM stage

19. Polysomnography in NREM and REM sleep

20. Polysomnography in REM sleep (patient with narcolepsy)

21. Sleep cycles Sleep cycles last about 80-120 minutes
NREM sleep lasts about minutes
REM sleep lasts about minutes (it is longer in the morning)

22. Abnormal EEG patterns
abnormalities of the background rhythms (areal differentiation, hemispheral organization…)
abnormal sleep patterns – narcolepsy
paroxysmal epileptiform abnormalities (generalized, focal…) - epilepsy
abnormal slow activity (generalized, focal…) – structural cerebral lesions
amplitude changes

23. Narcolepsy

24. Abnormal sleep patterns - narcolepsy
short latency to sleep onset (less than 5 min)
sleep onset REM periods
multiple sleep latency test (MSLT):
gives a patient 5 opportunities to fall asleep during the day
at 2-hour intervals EEG is recorded and the patient is given 20 min to fall asleep
if 2 or more sleep periods contain REM sleep, then a diagnosis of narcolepsy is highly likely

25. Abnormal EEG – amplitude changes:
local - reduction of amplitude due to:
superficial lesions in the cortex, rare
change of material between cortex and electrodes – subdural hematoma - flattening

26. Abnormal EEG – amplitude changes:
generalized – in deep coma
burst-suppression pattern or flat record

27. EEG in epilepsy interictal patterns – in intervals without seizures
epileptiform patterns – sharp waves, spikes, spike-and-wave complexes
local, as a focus
or generalized
ictal patterns – during seizure

28. Interictal patterns in epilepsy – local focus:

29. Interictal patterns in epilepsy – generalized:

30. Ictal patterns depend on the type of the seizure

31. Simple partial seizures - consciousness is not impaired - Jacksonian motor or somatosensory seizure

32. Simple partial seizures - single repetitive sharp waves

33. Complex partial seizures temporal lobe seizure with automatisms

34. Complex partial seizures - sharp theta waves 6Hz – temporal region

35. Generalized – absence seizures

36. Absence seizures – 3/sec generalized spike-and-wave discharges

37. Absence seizures

38. Generalized tonic-clonic seizures

39. Generalized tonic-clonic seizures
Tonic phase: generalized hypersynchronous 8-12Hz sharp waves and muscle artifacts
clonic phase – generalized rhythmic spikes form groups, followed by a slow wave
postictal coma – lower voltage arrhythmic activity, attenuation and slowing or flat EEG

40. Generalized tonic-clonic seizure – tonic and clonic phase

41. Generalized tonic-clonic seizure – clonic and postictal phase

42. EEG in structural cerebral lesions
Tumours
Abscesses
Contusions
Strokes
cause mainly local slow waves (theta or delta), they form a focus of slow waves

43. EEG in structural cerebral lesions

44. Brain tumours supratentorial deep or infratentorial
focal slow waves (irregular, persistent delta)
principles of localization of large tumours: “phase reversal”
deep or infratentorial
episodes of synchronous slow waves theta or delta

45. Phase reversal

46. Phase reversal

47. Activation procedures
Hyperventilation
in all patients, 4 minutes
absence of any change is normal
abnormal responses include epileptiform activity
intermittent photic stimulation
sleep recordings – after sleep deprivation

48. intermittent photic stimulation
rhythmic flashes, Hz
normal response – photic driving, reproduction of the rhythm - mostly frequencies of alpha, partially beta

49. intermittent photic stimulation
photic driving increases
Hyperthyroidism
tumours in the posterior fossa
Migraine (fast beta)
abnormal – photo convulsive response (epileptiform activity)

50. sleep recordings – after sleep deprivation
drowsiness and light sleep (stages 1 and 2 of NREM sleep) accentuate epileptiform abnormalities
all night sleep deprivation is required prior to taking the EEG

51. Easy, isn’t it ?