This document discusses EEG (electroencephalography), including: 1. EEG involves recording electrical activity of the brain using electrodes placed on the scalp. 2. EEG can help diagnose epilepsy, classify seizure types, localize epileptic zones, assess treatment response, and evaluate risks after stopping medication. 3. It describes normal sleep cycles and the brain wave patterns associated with each sleep stage. 4. Abnormal EEG patterns include epileptiform discharges like spikes and sharp waves, as well as non-epileptiform periodic discharges seen in conditions like encephalitis.

1. EEG
Dr Somasundaram pl
Junior resident
Department of paediatric
Guide – Dr Roopal Khobragade

2. Topics to discuss:
• 1. Normal sleep
• 2. Sleep cycle
• 3. Stages of sleep cycle
• 4. Electrophysiology of sleep
• 5. Abnormal EEG (seizure)
• 6. Abnormal EEG (non-epileptiform)

3. Definition
• EEG is the record of electrical activity of brain( superficial layer i.e. the
dendrites of pyramidal cells) by placing the electrodes on the scalp.

4. Role of EEG
• EEG is the most informative laboratory test in patients with epileptic seizures.
• It can play an important role in –
1) Diagnosis of epilepsy
2) Classification of epileptic seizure type and epilepsy syndromes
3) Localization of epileptogenic zone
4) Assessment of response to treatment
5) Estimation of risk of seizure recurrence after discontinuation of antiepileptic
medication
6) Non convulsive status epilepticus
7) Encephalitis and encephalopathy
8) Coma

5. Sensitivity and specificity of routine EEG
• Routine EEG after 1st unprovoked seizure
In adults- has sensitivity of 17.3% and specificity of 94.7%
In children- has sensitivity of 57.8% and specificity of 69.6%

6. Normal sleep
Duration: 8 hr
• NREM (75%):
1. Stage 1 (5%)
2. Stage 2 (45%)
3. Stage 3 (12%)
4. Stage 4 (13%).
NREM stage 3&4 together k/a deep sleep(25%) which is equivalent to duration of REM
sleep.
• REM (25%)

7. NREM (Orthodox) REM (Paradoxical)
Brain activity Lower than awake Increased except muscle tone
(muscle paralysis)
Pulse, BP,
respiration
Lower than awake state few
min to min variation
(synchronized sleep)
Higher than those in NREM &
often more than awake &
variable (desynchronized
sleep)
Body movement Involuntary & episodic Near total paralysis of skeletal
muscles
Temperature Homeothermic Thermoregulation altered
(Poikilothermic), ↑Core body
temperature
Dreaming Not remembered Remembered

8. As sleep progresses NREM sleep decreases & REM sleep increases

9. Arrangement of electrodes
• 4 Anatomincal Landmarks-
• Nasion-indentation between the forehead and the nose,
• Inion - a ridge at the midline over the occipital area,
• 2 Preauricular points - indentations just above the cartilage
that covers the external ear openings.
• Occasionally, additional electrodes
• Sphenoidal
• Suboccipital

10. Electrodes
• F = frontal
Fp = frontopolar
T = temporal
C = central
P = parietal
O = occipital
A = auricular(ear electrode).
• Even numbers- right side.
• Odd numbers - left side.
• "z" points to midline.

11. International 10-20 system (Jasper
1958)

12. Alpha waves - 8-13 Hz
Beta waves - >13 Hz
Theta waves - 3.5-7.5
Hz
Delta waves - 3 Hz or
less

13. • Beta is recorded over frontal & parietal region
• Alpha is recorded over occipital region
• Theta is seen in children & sleeping adults
• Delta is seen in infants & sleeping adults.

14. Different types of brain waves in normal EEG
Rhythm Frequency
(Hz)
Amplitude
(uV)
Recording
& Location
Alpha(α) 8 – 13 50 – 100 Adults, rest, eyes closed.
Occipital region
Beta(β) 14 - 30 20 Adult, mental activity
Frontal region
Theta(θ) 5 – 7 Above 50 Children, drowsy adult,
emotional distress
Occipital
Delta(δ) 2 – 4 Above 50 Children in sleep
D T A B

15. Brain activity: EEG findings
• Awake/ eyes open = Beta (frontal predominantly)
• Try to sleep (awake)/ eyes closed = Alpha (occipital)
• Relaxed with eyes closed: Alpha
• Active mental concentration: Beta
• Focussed attention: Gamma (highest frequency wave, >30 Hz).

16. EEG protocol
• To be recorded in both awake & sleep
• In sleep- Many of epileptiform activity can be picked
• In awake- tells about background activity and tells about cerebral function
• Sleep EEG is often required among infants and tells about cerebral
function.
• Sleep EEG requires 4 hours of sleep deprivation ( not needed routinely) –
this activates epileptiform activity which may be missed in routine EEG.
• Sedation( if required) – triclofos (20-50mg/kg/dose) or melatonin(2-
6mg/dose)

17. Activation procedure
• Sleep
• Sleep deprivation
• Hyperventilation- ask the child to take deep breath in & out. Useful in
diagnosis of absence seizures.
• Photic stimulation (intermittent) – 3 to 30hz
It is useful in diagnosis of photogenic epilepsies (eg- JME, etc)

18. • Eye opening and closing can enhance assessment of the posterior
dominant rhythm
• Eye closure may demonstrate abnormal activity in certain forms of epilepsy
(eg, benign occipital epilepsy)
• Fatigue rather than sleep per se is a main trigger.
• Sleep deprivation is an important activator of focal epileptiform
abnormalities.
• Hyperventilation is an activation procedure, it mainly influences absence
seizures & generalized 3hz spike & wave discharge.
• We typically hyperventilate patients for 3 mins , if features s/o absence
then we hyperventilate for 4 mins twice during EEG.

19. Hyperventilation in structural & vascular
conditions
• Hyperventilation in structural & vascular conditions can show focal
slowing.
• Hyperventilation results in hypocarbia and vasoconstriction
• Hence it should be cautiously used in case of known or suspected
moya moya disease, vascular disorders, complete stroke and
transient ischemic attacks.
• It is contraindicated in patients with significant cardiac disease,
severe respiratory problems and sickle cell disease.

20. Normal pattern seen in hyperventilation
• High amplitude rhythmic slowing may occur during hyperventilation
and clinically mimic an absence seizure & should not be considered as
an ictal pattern.

21. Photic stimulation
• Intermittent photic stimulation is primarily an activator of generalized spike
wave or polyspike wave – seen in idiopathic generalized or myoclonic
epilepsies.
• Generalized spike wave discharge that outlasts the duration of photic
stimulation is a genetic pattern and may be seen in individuals with no
history of epileptic seizures.
• Hence photosensitivity should be interpreted appropriately and should not
result in inappropriate management with AEDs.
• A spike wave discharge that outlasts the duration of the photic
stimulation or is associated with clinical signs such as myoclonic or
absence seizure, is a photoconvulsive response & is clearly abnormal
pattern.

22. Posterior dominant rythm
When the patient is relaxed with eyes closed, the background is usually
characterized by posteriorly dominant alpha rhythm, aka posterior dominant rythm

23. Reactivity
• EEG reactivity refers to a change in the EEG background activity in
response to external stimuli. on eye closure, evolution of alpha
dominant rhythm in occipital region
• In focal cerebral lesions, the posterior predominant frequency may
show unilateral impairment of reactivity to eye opening (Bancaud
phenomenon) or alerting. Lesions do not need to be in the occipital
lobes to produce these abnormalities of EEG reactivity

24. Bancaud phenomenon
Failure of alpha rhythm to accentuate even after eye opening, indicates
ipsilateral focal lesion of any lobe (not specific to occipital lobe)

25. Normal patterns
• Upto age of 4 months, the presence of sharp transients, which are
seen in many neonates without history of seizures and correlate
poorly with epileptic seizures or outcome.
• A posterior dominant rhythm first appears at the age of 3 months,
and is 3hz in the alert state.
• Evolution of posterior dominant rhythm
Age Hz
4 months 4
12 months 6
3 years 8
10 years 10-12

26. • By 3 years of age, the posterior dominant rhythm reaches alpha
frequency.
• It is best seen with eyes closed and in a relaxed state. It is blocked by
attention . Eg; eye opening or mental effort.

27. Stages of sleep & their patterns
• Step 1 NREM = Vertex waves (Theta)
• Stage 2 NREM = Sleep spindles & K complexes
• Deep sleep (stage 3 & 4 NREM): Delta wave
• REM sleep: Fast/ mixed frequency waves –saw tooth waves

28. Stages of sleep EEG pattern Somatic or
Behavioral changes
Alert Alpha activity on
eye closed
Desynchronization
on eye opening
Respond to verbal
commands
I (Drowsiness) Alpha dropout &
appearance of
vertex waves &
theta.
Reduced HR & RR
II (Light sleep) Sleep spindles,
vertex sharp
waves & K-
complexes
Reduced HR & RR
III ( Deep Sleep) Much slow
background K-
complexes
Reduced HR & RR

29. IV (very deep
sleep)
Synchronous delta
waves, some K-
complexes
Reduced HR & RR
REM sleep
(paradoxical
sleep)
Desynchronization
with faster
frequencies
HR, BP & RR irregular
Marked hypotonia
Rapid eye movement
50 – 60 /min.
Dreaming threshold
of arousal

30. Stage 1 NREM: Vertex/ Theta (Lightest stage
of sleep)

31. • Stage 2 NREM:
• o Sleep spindles & K complexes
• o Largest % of sleep

32. • K complex- characteristic biphasic
Negative-positive waves lasting more
Than 0.5 seconds.
• Large-amplitude delta frequency waves,
sometimes with a sharp apex.
• They can occur throughout the brain and
more prominent in the bifrontal regions.
• Usually symmetric, they occur each time
the patient is aroused partially from
sleep.
• Sometimes followed by runs of
generalized rhythmic theta waves- an
arousal burst.
K complex

33. • Sleep spindles
• Sleep spindles- spindle shaped rhythmic waves which gradually
increase & then decrease in amplitude, lasts around 0.5 to 3 sec &
generated every 3-6 sec
• Groups of waves during many sleep stages, especially in
stage 2.
• Frequencies in the upper levels of alpha or lower levels of
beta.
• Lasting for a second or less, they increase in amplitude
initially and then decrease slowly.
• They usually are symmetric and are most obvious in the
parasagittal regions.

34. • Delta: 20-50% - > Stage 3
• Delta: >50% -> Stage 4
• o Deepest sleep
• o Decreases with age
• o Most relaxed stage

35. REM Sleep
• Burst activity
• No EMG (due to muscle paralysis)
• Penile erection +
• Muscle atonia
• ↑Pulse, Respiration
• Peak at 5-6 AM
• Saw tooth waves

36. Changes in brain waves during different
stages of sleep & wakefulness

38. Sleep Spindle
K - complex

39. EEG Artifacts
• Biological artifacts
• Eye artifacts (including eyeball, ocular muscles and eyelid)
• ECG artifacts
• EMG artifacts
• Glossokinetic artifacts (minor tongue movements)
• External artifacts
• Movement by the patient
• settling of the electrodes
• Poor grounding of the EEG electrodes
• the presence of an IV drip

40. Artifact- eye blink

41. Muscle activity

42. Amplitude abnormalities
• Amplitude differences need to be interpreted with caution
since isolated differences in amplitude may occur as a
normal finding.
• Alpha rhythm may be increased in amplitude on one side,
most often the right, by as much as a 2:1 ratio.
• Less commonly, the alpha rhythm of the left hemisphere is
increased by as much as a 3:2 ratio.
• More pronounced differences in background amplitude are
abnormal.

43. • Markedly diminished amplitude on one side-
– Abnormalities of cortical gray matter
– With excess fluid between the cortex and recording electrodes.
– Ischemic stroke with gray matter involvement
– Subdural hematoma
– Sturge-Weber syndrome.

44. Frequency abnormalities
• Alterations in frequency typically are most useful in
the assessment of diffuse rather than focal cerebral
disturbances.
• The EEG background frequency of the 2 hemispheres
should be within 1 Hertz (Hz).
• Any greater difference is indicative of a lateralized
EEG abnormality on the side with the slower
background

45. Abnormal EEG
• •It is of 2 types:
• 1. Epileptiform
• 2. Non-epileptiform

46. Abnormal EEG (Epileptiform
discharges)
• •It is of 3 types:
• 1. Spike waves: <70 ms
• 2. Sharp waves: 70-200 ms
• 3. Slow waves: >200 ms.
• O<1/3rd of 200 ms: Spike
• o >1/3rd - Full of 200 ms: Sharp
• o >200 ms: Slow.

48. • Similarly, spike waves can be:
• 1. Monophasic
• 2. Biphasic
• 3. Triphasic
• 4. Polyphasic.

49. Spike, generalized.
High amplitude and the aftergoing background suppression and slow
wave.

50. Spike, generalized.
Significant spikes usually are followed by a slow wave,. Generalized
spikes are typically maximal frontally. This is typical of the primary
(ie, idiopathic, genetic) epilepsies. .

51. • Slow spike & wave (1.5-2 Hz) - Lennox-Gastaut syndrome
(LGS)
• 3 Hz spike & wave - Absence seizure
• Fast spike & wave (4-6 Hz) - Myoclonus (poly spike & wave)

52. Slow spike-wave complexes (SWC).
In addition to being slower, this is also less monomorphic than the 3-Hz SWC- the
Lennox-Gastaut type.

53. Generalized burst (3 Hz: Absence seizure)

54. Fast poly spike & wave in a patient with
Juvenile myoclonic epilepsy (polyspike, generalized)

55. Polyspike, generalized.
Aftergoing slow wave -typically juvenile myoclonic epilepsy

56. GTCS VS PARTIAL

57. Common EEG abnormalities
• MC EEG abnormality: Diffuse slowing of background rhythms
• Triphasic wave: Seen in Toxic metabolic encephalopathies (Ex: Hepatic
encephalopathy)
• Periodic lateralising epileptiform discharges (PLED)
• Periodic triphasic complexes (sharp waves): Commonly seen in
crutzfeld Jacob disease

58. Breach rhythm
Asymmetric increase of EEG activity over skull defect
( Rt. Fronto-central region)

59. Background slowing
Mild diffuse cortical dysfunction

60. Intermittent slowing- Generalized

61. Intermittent slowing regional-pathologic

62. Continuous slowing regional-pathologic

63. Non-epileptiform EEG/ Periodic
discharges
• Characteristics:
• 1. Periodic discharges of high amplitude
• 2. May be spike or sharp
• 3. Recurring at periodic interval
• 4. Most important EEG finding for an ongoing CNS disease or CNS
infection
• 5. There are 4 types of periodic discharges
• I. Burst suppression
• II. Repetitive sharp waves
• III. Periodic triphasic waves
• IV.Generalized periodic waves.

64. • 1. CJD: Periodic triphasic complexes (sharp waves)
• 2. SSPE: Periodic giant waves
• 3. Herpes encephalitis: Periodic lateralising epileptiform
discharges (PLED)
• 4. Burst suppression: Cerebral anoxia
• * (Burst pattern: Absence seizure).

65. CJD (Periodic triphasic / sharp waves,
Interval: 0.5-2 sec)

66. Herpes encephalitis (PLED, present in one
sided fronto-temporal lobe)
Periodic – 1/sec at a regular interval
Lateralising- involves one side
Epileptiform discharges- high amplitude waves which are separated by other
low amplitude waves

67. Burst suppression (Burst followed by
suppression)

68. Hypsarrhythmia
Consists of diffuse giant waves (high voltage, >400 mV) with a chaotic
background of irregular, multifocal spikes and sharp waves

69. Encephalitis and encephalopathy
• Frequency of alpha rhythm slows-even before consciousness is
altered
• Slow alpha rhythm intermixed with sporadic theta activity
• Slower theta activity become generalized and less reactive to
external stimuli
• Slowing into delta range

70. Severe, generalized, slow-wave abnormality in a
10 year- old boy with encephalitis

71. SSPE showing a hypsarrythmia pattern with periods of flattening

72. Sharp and slow wave complexes recurring
every 6 seconds :SSPE

73. Encephalopathic patterns in uremia
- shows continuous theta and delta activity

74. EEG in coma
• Classification system for coma
GRADES OF COMA FEATURES
Grade 1 Regular alpha & some theta
Grade 2 Predominant theta
Grade 3 Widespread delta or some spindle coma
Grade 4 Burst suppression pattern/alpha coma
Grade 5 Flat

75. Alpha coma
EEG pattern in alpha frequency predominantly in frontal region, non
reactive to any external stimuli – seen in comatosed patients

76. Spindle coma
Generalized high-voltage delta activity with sleep spindles superimposed.
Spindles are more widespread than normal sleep, although similar
morphology. Has better prognosis when compared to alpha coma.