will review details about neuro-physiological basis for seizures, and some basic information about eeg reading and its basics

1. Dr. Amit Vatkar
MBBS, DCH, DNB Pediatrics
Fellow in Pediatric Neurology, Mumbai
Trained in Neurophysiology & Epilepsy, USA
Contact No. : +91-8767844488
Email: vatkaramit@yahoo.com
NEUROPHYSIOLOGY
OF SEIZURES AND EEG

2. NEUROPHYSIOLOGY
Initiation Phase :
1. High frequency bursts of AP
2. Hyper synchronization
Bursting activity :
Long lasting depolarisation of Neuronal membrane
due to influx of EC Ca2+
Opening of Na+ channels
influx of Na+
Generation of repetitive AP

3. PROPAGATION PHASE :
1.Increased in EC K+
(Blunts hyperpolarization and depolarise
neighbouring neuron)
2. Accumulation of Ca2+ in presynaptic terminals
(enhanced NT release)
3. Depolarisation – induced Activation of the N-
methyl – D Aspartate (Ca++ influx * Neuronal
activation)

4. Mechanisms for Bursting Activity :
Intrinsic to Neuron :
Changes in
• conductance of ion channels
• response characteristics of membrane receptors
• Cytoplasmic buffering
• Second messenger systems
• Protein expression as determined by gene
transcription, translation and post translational
modification

5. Extrinsic to Neuron :
Changes in
1.Amount or type of NT present at the
synapse
2. Modulation of receptors by EC ions and
other molecules
3. Temporal & spatial properties of synaptic
and non synaptic input

6. Mechanism of origin of generalised spike and
wave discharges in Absence Seizures
Related to oscillatory rhythm (by circuits
connecting thalamus & cortex)
Oscillatory behaviour involves an interaction
between GABA -B receptor, T-Type Ca2+
channels and K+ channels located within
thalamus

7. Mechanism of Epileptogenesis :
Transformation of a normal neuronal network into one
that is chronically hyper excitable
 CNS injury  Lowering of seizure threshold
 Structural changes in Neuronal networks
Eg. I - MTLE
1) highly selective loss of neurons
2) Reorganisation or sprouting of surviving
neuron
II - Head Injury
 Alterations in intrinsic bio chemical properties o
cells eg. Chr changes in Glutamate Receptor

8. MECHANISM OF INTER ICTAL AND ICTAL
EVENTS

9. APPLIED IMPORTANCE :
AED appear to act primarily by blocking the initiation of
spread of seizures
Inhibition of Na+ dependent AP – phenytoin CBZ,
Lamotrigine, Topiramate
Inhibition of voltage gated Ca++ channels – phenytoin
Decrease glutamate release – Lamotrigine
Potentiation of GABA receptor function 
Benzodiazepine
Increased in availability of GABA  valproic acid,
gabapentin, Tiagabine
Inhibition of T. type Ca2+ channels in thalamic neuron –
Ethosuximide, valproic acid

11. DefinitionDefinition
EEG Stands forEEG Stands for ElectroencephalographyElectroencephalography
EEG signals are based upon the movement ofEEG signals are based upon the movement of
electrical charges in biological tissue.electrical charges in biological tissue.
These electrical charges are associated with ionsThese electrical charges are associated with ions
(+ve or(+ve or ––ve charged) such as sodium (Na), potassiumve charged) such as sodium (Na), potassium
(K).(K).
This activity is actually a measure of the brainThis activity is actually a measure of the brain’’ss
functionfunction rather thanrather than structurestructure..

12. Definition Contd..Definition Contd..
EEG typically is the recording of potentialEEG typically is the recording of potential
differences between two points (with one or bothdifferences between two points (with one or both
electrodes on the scalp)electrodes on the scalp)
Amplitude scale typically in microvolts (Amplitude scale typically in microvolts (µµV)V)
Typical EEG, as recorded from the surface of theTypical EEG, as recorded from the surface of the
head is attenuated by ~75% from direct corticalhead is attenuated by ~75% from direct cortical
recordings.recordings.
Compared with ECG (typically in the mV range),Compared with ECG (typically in the mV range),
EEG signal is 1000 times smallerEEG signal is 1000 times smaller
Complexity of EEG is greater than ECG and notComplexity of EEG is greater than ECG and not
as clearly definedas clearly defined

13. Electrode PlacementElectrode Placement
Ten Twenty SystemTen Twenty System
In 1958 it was decided there should be anIn 1958 it was decided there should be an
internationally agreed system for the placement ofinternationally agreed system for the placement of
EEG electrodesEEG electrodes
Known as the 10/20 system.Known as the 10/20 system.
Certain anatomical landmarks on the skull, such asCertain anatomical landmarks on the skull, such as
the nasion, inion and preauricular notches arethe nasion, inion and preauricular notches are
used to determine the relative positioning ofused to determine the relative positioning of
electrodes.electrodes.

14. Electrode PlacementElectrode Placement
Ten Twenty SystemTen Twenty System
EEG Technician measures the skull and marksEEG Technician measures the skull and marks
positions usually with chinagraph pencil.positions usually with chinagraph pencil.
Points marked at the appropriate 10% and 20%Points marked at the appropriate 10% and 20%
intervals.intervals.
Relative distanceRelative distance between pairs of electrodesbetween pairs of electrodes
remains the same, regardless of absolute headremains the same, regardless of absolute head
size.size.
Electrode caps based upon the 10-20 system mayElectrode caps based upon the 10-20 system may
also be used for clinical recording.also be used for clinical recording.

15. Electrode PlacementElectrode Placement
A : Lateral left-sided view of head
B: Superior view of head
C: 10-10 International System
(or extended 10-20 System)
• Even Numbers: correspond to right hemisphere
• Odd Numbers: correspond to left hemisphere
• Subscript Z: corresponds to the midline
• Numbers increase laterally from the midline
Abbreviations:
N: Nasion
Fp: Frontal polar
AF: Antero-Frontal (Anterior Frontal)
F: Frontal
FT: Fronto-Temporal (Frontal-Temporal)
FC: Fronto-Central (Frontal-Central)
T: Temporal
C: Central
TP: Temporo-Parietal (Temporal-Parietal)
CP: Centro-Parietal (Central-Parietal)
P: Parietal
PO: Parieto-Occipital (Parietal-Occipital)
O: Occipital
I: Inion
Pg: Nasopharyngeal

16. Electrode PlacementElectrode Placement
Special Note:
Ambiguous labels between
10-20 & 10-10 System
T7 ≡ T3
P7 ≡ T5
T8 ≡ T4
P8 ≡ T6

17. Electrode PlacementElectrode Placement
 Signals (commonly referred to asSignals (commonly referred to as tracestraces) are) are
generally recorded between pairs of electrodes ongenerally recorded between pairs of electrodes on
both hemispheres of the brain.both hemispheres of the brain.
 Recording from pairs of adjacent electrodesRecording from pairs of adjacent electrodes
commonly referred to ascommonly referred to as bipolarbipolar
 Recording of electrode potentials with respect to aRecording of electrode potentials with respect to a
default or global reference electrode referred to asdefault or global reference electrode referred to as
monopolar, unipolar or referentialmonopolar, unipolar or referential
 They are measured in linked chains of bipolarThey are measured in linked chains of bipolar
electrodes from front to back and transversely acrosselectrodes from front to back and transversely across
the head.the head.
 Convention regards the polarity as Negative, suchConvention regards the polarity as Negative, such
that a negative potential difference is represented bythat a negative potential difference is represented by
an upward deflection in the trace.an upward deflection in the trace.

18. EEG Frequency Bands
 Alpha 8.1 – 13 Hz
 Beta ~13 – 20 Hz
 Theta 4.1 – 8 Hz
 Delta 0.5 – 4 Hz
 Gamma* ~20 - 55 Hz
* Frequencies in Gamma range or higher often referred to as high
frequency Beta
EEG is commonly divided into following frequency bands:

19. EEG and AgeEEG and Age
 Normal EEG has alpha as the dominant frequencyNormal EEG has alpha as the dominant frequency
 In infants and young children, may observe aIn infants and young children, may observe a
predominance of theta activity or low frequency alphapredominance of theta activity or low frequency alpha
 In the elderly, also may have a tendency to see someIn the elderly, also may have a tendency to see some
slowing in background activity, again alpha-thetaslowing in background activity, again alpha-theta
boundaryboundary
 Some epilepsy syndromes have specific EEGSome epilepsy syndromes have specific EEG
changes that are only present within specific agechanges that are only present within specific age
rangesranges
EEGEEG shouldshould be interpreted with some backgroundbe interpreted with some background
knowledge of the patient, and age is an importantknowledge of the patient, and age is an important
discriminant between what may be acceptable as adiscriminant between what may be acceptable as a
normal EEG variant and a specific abnormalitynormal EEG variant and a specific abnormality

20. EEG MontagesEEG Montages
 EEG signals are typically represented as aEEG signals are typically represented as a
series of waveforms on paper or monitorseries of waveforms on paper or monitor
 They represent the potential difference betweenThey represent the potential difference between
electrodes pairselectrodes pairs
 The order and sequence of these waveformsThe order and sequence of these waveforms
are defined asare defined as montagesmontages
 Montages are particularly useful in that theMontages are particularly useful in that the
magnitude and orientation of the EEGmagnitude and orientation of the EEG
generators that may not be clearly defined ingenerators that may not be clearly defined in
one montage may become apparent in another.one montage may become apparent in another.

21. ReferentialReferential
 EEG trace of interest is defined by the differenceEEG trace of interest is defined by the difference
between the specific electrode (ie. O1) and a cephalicbetween the specific electrode (ie. O1) and a cephalic
reference point referenced to a single electrode.reference point referenced to a single electrode.
 i.e. Fp2i.e. Fp2 –– REF, Fp1REF, Fp1 –– REF, etc.REF, etc.
DifferentialDifferential
 EEG trace is defined by electrode referenced to anotherEEG trace is defined by electrode referenced to another
(more proximally located) electrode on the head ie Fp2(more proximally located) electrode on the head ie Fp2
–– F4F4
 Differential (commonly referred to asDifferential (commonly referred to as BipolarBipolar) is the) is the
most flexible montage type and is most commonly usedmost flexible montage type and is most commonly used
or modified for assessing focal EEG abnormalities.or modified for assessing focal EEG abnormalities.
EEG MontagesEEG Montages

22. Types of EEG RecordingTypes of EEG Recording
Routine EEGRoutine EEG
20 – 30 minute test20 – 30 minute test
ScreeningScreening
Eyes Open & Eyes ClosedEyes Open & Eyes Closed
Includes provocative techniquesIncludes provocative techniques

23. Types of EEG RecordingTypes of EEG Recording
Ambulatory EEGAmbulatory EEG
Patient is fitted with a small recorder for 24Patient is fitted with a small recorder for 24
hours – patient can then have their EEGhours – patient can then have their EEG
recorded whilst in their normal environmentrecorded whilst in their normal environment

24. Types of EEG RecordingTypes of EEG Recording
Long term MonitoringLong term Monitoring
Typically ranges from 3 hours to 5 days.Typically ranges from 3 hours to 5 days.
(Generally no longer than 2 weeks)(Generally no longer than 2 weeks)
Performed if Routine EEG recording showsPerformed if Routine EEG recording shows
nothing, but clinical history of seizures suggestivenothing, but clinical history of seizures suggestive
extended recording, usually with video used to tryextended recording, usually with video used to try
to record unusual activity.to record unusual activity.
Clearly define the relationship between electricalClearly define the relationship between electrical
EEG changes and clinical eventsEEG changes and clinical events
NOTE:NOTE: A large percentage of patients with epilepsy may displayA large percentage of patients with epilepsy may display
normal EEG until an actual episode or “attack” occurs, extendednormal EEG until an actual episode or “attack” occurs, extended
recording along with supervised modifications to medications mayrecording along with supervised modifications to medications may
be required to clearly elucidate the seizure typebe required to clearly elucidate the seizure type..

25. Visual EEGVisual EEG AssessmentAssessment
 Determine dominant frequency of background activityDetermine dominant frequency of background activity
 Determine dominant amplitudeDetermine dominant amplitude
 Compare reactivity to eye opening compared toCompare reactivity to eye opening compared to
background (ie. while eyes are closed)background (ie. while eyes are closed)
 Establish symmetry of activity from both hemispheresEstablish symmetry of activity from both hemispheres
as well as comparison between cerebral lobesas well as comparison between cerebral lobes
 Discriminate sharply contoured waves or spikes asDiscriminate sharply contoured waves or spikes as
arising from artefact or as truly abnormal activityarising from artefact or as truly abnormal activity
 Compare reactivity to provocative techniques ofCompare reactivity to provocative techniques of
photic stimulation and hyperventilationphotic stimulation and hyperventilation

26. Provocative Techniques ActiveProvocative Techniques Active
HyperventilationHyperventilation
Patient breathes deeply, continuously, for typicallyPatient breathes deeply, continuously, for typically
about 3 minutes.about 3 minutes.
Hyperventilation rapidly removes COHyperventilation rapidly removes CO22 from thefrom the
blood stream and modifies blood pH levels slightlyblood stream and modifies blood pH levels slightly
Blood vessels constrictBlood vessels constrict
Pronounced EEG slow activity is observedPronounced EEG slow activity is observed
This increased synchronisation may evoke aThis increased synchronisation may evoke a
seizure in certain individualsseizure in certain individuals

27. Example of generalised
slowing associated with
hyperventilation.

28. Photic StimulationPhotic Stimulation
High Intensity light presented to patient at variousHigh Intensity light presented to patient at various
frequencies (1-40 Hz) for brief intervals (typicallyfrequencies (1-40 Hz) for brief intervals (typically
5-10 seconds)5-10 seconds)
Small percentage of patients with epilepsy areSmall percentage of patients with epilepsy are
photo-sensitivephoto-sensitive – may have episodes that are– may have episodes that are
precipitated by flickering light.precipitated by flickering light.
Normal EEG variant –Normal EEG variant – Photo DrivingPhoto Driving wherewhere
changes in EEG show a direct frequency lockedchanges in EEG show a direct frequency locked
response to stimulation.response to stimulation.
Provocative Techniques ActiveProvocative Techniques Active

29. Example of photic driving,
maximal activation from
occipital electrodes, and
discharges clearly locked
to stimulus.

30. Sleep DeprivationSleep Deprivation
 Most generalised epilepsies are enhanced by slowMost generalised epilepsies are enhanced by slow
wave sleep, and some focal epilepsies are likely towave sleep, and some focal epilepsies are likely to
generalise from the abnormal area.generalise from the abnormal area.
 Sleep deprivation is likely to exacerbate suchSleep deprivation is likely to exacerbate such
seizures and therefore it may provide a higher yieldseizures and therefore it may provide a higher yield
of detecting an EEG abnormality from a routine EEGof detecting an EEG abnormality from a routine EEG
if patient is deprived of sleep prior to recording.if patient is deprived of sleep prior to recording.
 Commonly used technique for hospital inpatientsCommonly used technique for hospital inpatients
when undergoing long-term monitoring for diagnosticwhen undergoing long-term monitoring for diagnostic
or pre-surgical workupor pre-surgical workup
Provocative Techniques PassiveProvocative Techniques Passive

31. Maturation of EEG in children :
1.Posterior Dominant rhythm maturation
2. Hyper ventilation  higher amplitude slow activity
3. Posterior slow waves of youth
4. More theta anteriorly
5. Hypnagogic hypersynchrony
6. Sharp & high voltage
sleep activity

32. E.E.G IN EPILEPSY
IDEAL IN EVERY PATIENT
1. DIAGNOSIS OF EPILEPSY-ABSENCE EPILEPSY
BENIGN ROLANDIC EPILEPSY
MYOCLONIC EPILEPSY
2. TYPE OF SEIZURE
3. LOCALISATION IN PARTIAL SEIZURE
4. ETIOLOGY - LESIONAL EPILEPSY
ENCEPHALOPATHY - PLEDS
- HEPATIC
- SSPE
- HSE
- CJD
5. FOLLOW UP
6. STATUS EPILEPSY

33. Epileptiform Discharge :
Different from the surrounding activity
High voltage
Asymmetrical with a longer and larger second half
Has more than one phase
Tend to have an after
going slow wave

34. Epileptiform Discharges :
1.Spike
2.Sharp wave
3. Spike and wave complex
4. Polyspike & wave complex
5. Sharp & slow wave complex
6. Polyspike complex
7. Multiple sharp wave complex
8. Synchronous spike and wave discharges
9. Asynchronous discharges

35. SPIKE SHARP SPIKE & WAVE SHARP & SLOW
WAVE
SLOW SPIKE AND
WAVE
POLY SPIKE AND
WAVE
MULTIPLE SHARP
AND SLOW WAVE
POLY SPIKE MULTIPLE SHARP COMPLEXES

38. EEG features in various Epilepsy
I – Simple Partial seizures
Normal in 60 – 80 %
In some patients, periodic sharp activity or very
focal rhythmic activity limited to only a few
electrodes.
II – Complex partial seizures :
 Mesial frontal / orbito frontal origin
- may be without scalp EEG changes
 Temporal lobe origin  brief discharges
termed epileptiform spikes or sharp waves

40. III - Generalised Absence Seizures :
High voltage
Frontally dominant
Synchronous, symmetrical, regular and
rhythmic 2.5 to 4 Hz Spike and wave activity
IV - Generalised atypical absence Seizures
Frequency < 2.5 Hz
Slight post ictal slow activities
Asymmetrics are common
More regional distribution anteriorly

43. V – Generalised tonic seizure :
Generalised 10- Hz rhythmic activity or
Generalised high frequency low voltage activity

45. VI - Generalised atonic seizure :
Brief generalised spike and wave
discharges followed immediately by
diffuse slow waves

47. VII – Generalised tonic clonic seizure :
Tonic phase :
10 Hz rhythmic discharge that evolves
into high amplitude generalised polyspike
discharges.
Clonic phase :
High amplitude activity is typically
interrupted by slow waves to create a spike
and wave pattern

49. VIII – Infantile spasm :
 Begins with abrupt generalised eletro
decremental response of EEG with
generalised attenuation of back ground
frequencies with superimposed beta or
alpha range activity lasting from < 1
sec to several seconds

51. IX – Juvenile Myoclonic Epilepsy :
Bilaterally synchronous fast 4-6 Hz
spike & wave discharges synchronous with
myoclonus

53. X – Lennox – Gastaut syndrome
Slow posterior background
Slow generalised spike and wave
activity at 1.5 – 2 Hz (hall mark)

55. EEG PATTERNS IN SELECTED SPECIFIC
CONDITIONS
Herpes Simplex encephalitis :
Periodic lateralised epileptiform discharges in
temporal or fronto temporal area
SSPE : (Subacute sclerosing Pan Encephalitis)
Long interval generalised periodic discharges

58. Hypoxic Ischemic encephalopathy
1. Generalised asynchronous / bisynchronous slow
activity
2. Generalised attenuation
3. Alpha coma
4. Theta coma
5. Spindle coma
6. Periodic discharges  may be synchronous or
independent
7. Burst suppression pattern
 epochs of relative flattening of back ground
(suppression) alternating with epochs of mixed
frequency EEG activity (bursts)

60. LIMITATIONS OF EEG
NORMAL EEG. DOES NOT RULE OUT
NORMAL VARIANTS MISTAKEN FOR EPILEPSY
NOT SENSITIVE FOR STRUCTURAL LESION
NOT A GOOD GUIDE FOR
- SEIZURE CONTROL
- DRUG WITHDRAWAL
ALWAYS CORRELATE CLINICALLY

61. Dr. Amit Vatkar
Pediatric Neurologist, Navi Mumbai
MBBS, DNB
Email: vatkaramit@yahoo.com
Contact No.: +91-8767844488
Visit us at: http://pediatricneurology.in/
THANK
YOU !