Introduction to EEG
for non-epileptologists working in
seizure prediction and dynamics
Richard Wennberg, MD, FRCPC
University of Toronto
IWSP4, Kansas City, 2009
1. EEG source
•
•
•
•
cortical pyramidal cells
voltage fluctuations in space/time
summated EPSPs/IPSPs
dependent on neural “synchrony”
2. EEG oscillations
• Normal
– (alpha, beta, mu, gamma, sleep spindles/delta)
– generated in cortex
– varying degrees of thalamocortical
interdependence
• Abnormal
– (seizures, burst-suppression)
3. EEG sharp transients
• Normal
– Vertex sharp waves, positive occipital sharp
transients of sleep (POSTS), benign epileptiform
transients of sleep (BETS) or small sharp spikes;
eye blinks, EKG, EMG
• Abnormal
– Epileptiform spikes, polyspikes, spike and waves,
sharp waves, sharp and slow waves
– Periodic complexes (lateralized and generalized),
triphasic waves
International (10-20)
Electrode Placement
Gloor, J Clin Neurophysiol, 1985
Gloor, J Clin Neurophysiol, 1985
Gloor, J Clin Neurophysiol, 1985
Pedley and Traub. In: Daly and Pedley, eds. Current Practice of Clinical EEG, 1990
Pedley and Traub. In: Daly and Pedley, eds. Current Practice of Clinical EEG, 1990
Steriade. In: Niedermeyer and Lopes da Silva, eds. Electroencephalography, 1993
EEG examples
Subject awake, resting. Normal posterior alpha rhythm disappears with eye opening (*).
High frequency activity at end of figure after eye opening is muscle artifact. Anterior-posterior bipolar montage.
LFF 0.5 Hz, HFF 70 Hz, this and all other figures.
Stage II sleep. K-complex (*); Sleep spindles (**). Anterior-posterior bipolar montage.
Burst of generalized 3 Hz spike and wave activity (*). Primary generalized epilepsy. Anterior-posterior bipolar montage.
Generalized, bilaterally synchronous, 3 Hz spike and wave activity in a different patient with primary generalized epilepsy.
Referential montage; reference = linked ears.
Primary generalized epilepsy: spike and wave bursts
Juvenile myoclonic epilepsy
Generalized, bilaterally synchronous bursts of spike and wave activity in another patient with primary generalized
epilepsy, subtype juvenile myoclonic epilepsy. Referential montage; reference = linked ears.
Primary generalized epilepsy: transition to tonic-clonic seizure
Juvenile myoclonic epilepsy
In this condition, bursts of spike and wave activity increase in frequency in the morning hours after awakening in a true
“pre-ictal period” that may – or may not – result in a transition to a generalized tonic-clonic seizure.
Primary generalized epilepsy: transition to tonic-clonic seizure
High amplitude “hypersynchrony”
Same seizure transition as previous figure, shown here at slower sweep speed.
Bilateral temporal lobe (“focal”, “partial”) interictal epileptiform activity.
Independent sharp and slow wave complexes over right (*) and left (**) anterior-mid temporal regions.
Temporal lobe epilepsy. Anterior-posterior bipolar montage.
Ictal EEG showing focal rhythmic seizure pattern localized to right temporal region
(“equipotentiality” at F8-T4). Temporal lobe epilepsy. Anterior-posterior bipolar montage.
Patient with bilateral hippocampal sclerosis, global developmental delay, medically-refractory complex partial seizures
Interictal EEG during drowsiness in a different patient showing unilateral right anterior temporal lobe spikes
(“phase reversing” at Zg2, F8, F10)
Patient with bilateral hippocampal sclerosis, global developmental delay, medically-refractory complex partial seizures
Ictal EEG showing unilateral right temporal lobe seizure (with “equipotentiality” at Zg2-T4, F8-T4, F10-T10)
(note different sensitivity and time scale compared with preceding, interictal EEG figure from same patient)
Artifacts
Reference electrodes
Why should the non-epileptologist care about
artifacts and reference electrodes?
Two examples
– EEG studies of beta and gamma oscillations in
cognition would appear to have been analyzing
mainly muscle artifact
• Whitham et al. Clin Neurophysiol 2008;119:1166-75 and
Clin Neurophysiol 2007;118;1877-88
– The need for a reference electrode in EEG affects
phase synchronization studies; resulting amplitude
variations influence the phase locking analyses
• Guevara et al. Neuroinformatics 2005;3:301-13
Eye blink, horizontal eye movements, frontalis and temporalis EMG, lateral rectus EMG, pulse artifacts.
CZ-C3
C3-T3
T3-SP1
SP1-SP2
SP2-T4
T4-C4
C4-CZ
EOG1-EOG2
FP1-F7
F7-T3
T3-T5
T5-O1
FP2-F8
F8-T4
T4-T6
T6-O2
FP1-F3
F3-C3
C3-P3
P3-O1
FP2-F4
F4-C4
C4-P4
P4-O2
EKG
Comment
Eye Blink
C3 pulse artifact
C3 pulse artifact
C3 pulse artifact
Eyes left
Eyes right
100 uV
1 sec
Combined circular and anterior-posterior bipolar montage.
Eye blink, horizontal eye movements, frontalis and temporalis EMG, lateral rectus EMG, pulse artifacts.
F7-Pz
T3-Pz
T5-Pz
Fp1-Pz
F3-Pz
C3-Pz
P3-Pz
O1-Pz
Fz-Pz
Cz-Pz
Pz-Pz
Fp2-Pz
F4-Pz
C4-Pz
P4-Pz
O2-Pz
F8-Pz
T4-Pz
T6-Pz
Comment
Eye Blink
C3 pulse artifact
C3 pulse artifact
C3 pulse artifact
Eyes left
Eyes right
100 uV
1 sec
Referential montage; reference = Pz.
Eye blink, horizontal eye movements, frontalis and temporalis EMG, lateral rectus EMG, pulse artifacts.
F7-Fz
T3-Fz
T5-Fz
Fp1-Fz
F3-Fz
C3-Fz
P3-Fz
O1-Fz
Fz-Fz
Cz-Fz
Pz-Fz
Fp2-Fz
F4-Fz
C4-Fz
P4-Fz
O2-Fz
F8-Fz
T4-Fz
T6-Fz
Comment
Eye Blink
C3 pulse artifact
C3 pulse artifact
C3 pulse artifact
Eyes left
Eyes right
100 uV
1 sec
Referential montage; reference = Fz.
Eye blink, horizontal eye movements, frontalis and temporalis EMG, lateral rectus EMG, pulse artifacts.
F7-C3
T3-C3
T5-C3
Fp1-C3
F3-C3
C3-C3
P3-C3
O1-C3
Fz-C3
Cz-C3
Pz-C3
Fp2-C3
F4-C3
C4-C3
P4-C3
O2-C3
F8-C3
T4-C3
T6-C3
Comment
Eye Blink
C3 pulse artifact
C3 pulse artifact
C3 pulse artifact
Eyes left
Eyes right
100 uV
1 sec
Referential montage; reference = C3.
Eye blink, horizontal eye movements, frontalis and temporalis EMG, lateral rectus EMG, pulse artifacts.
F7-Av12
T3-Av12
T5-Av12
Fp1-Av12
F3-Av12
C3-Av12
P3-Av12
O1-Av12
Fz-Av12
Cz-Av12
Pz-Av12
Fp2-Av12
F4-Av12
C4-Av12
P4-Av12
O2-Av12
F8-Av12
T4-Av12
T6-Av12
Comment
Eye Blink
C3 pulse artifact
C3 pulse artifact
C3 pulse artifact
Eyes left
Eyes right
100 uV
1 sec
Referential montage; reference = common average (of electrodes F3, F4, T3, C3, C4, T4, T5, P3, P4, T6, O1, O2).
Eye blink, horizontal eye movements, frontalis and temporalis EMG, lateral rectus EMG, pulse artifacts.
F7-aF7
T3-aT3
T5-aT5
Fp1-aFp1
F3-aF3
C3-aC3
P3-aP3
O1-aO1
FZ-aFz
CZ-aCz
PZ-aPz
Fp2-aFp2
F4-aF4
C4-aC4
P4-aP4
O2-aO2
F8-aF8
T4-aT4
T6-aT6
Comment
Eye Blink
C3 pulse artifact
C3 pulse artifact
C3 pulse artifact
Eyes left
Eyes right
100 uV
1 sec
Referential montage; reference = Laplacian.
EEG cannot “see” deep into the brain
Spontaneous activity in, e.g.,
mesial temporal regions,
interhemispheric frontal lobe structures,
thalamus
is NOT apparent on scalp EEG
Comparison of intracranial interictal epileptiform activity recorded during sleep with simultaneous scalp EEG. Focal spikes in
left and right hippocampus (LH and RH), electrode contacts LHD1 and RHD1, show no scalp EEG correlates; more diffuse
right temporal spike and wave complexes (RT) apparent at multiple contacts of right temporal depth electrode (RHD1-4) are
associated with visible epileptiform potentials on scalp EEG (channels F8, T4). Referential montage; reference = common
average 10-20 electrodes. Top 16 channels = scalp EEG. Channels 17-20 and 21-24 = left and right, respectively, temporal
depth electrode recordings. Sensitivity = 15μV/mm for scalp EEG, 50 μV/mm for intracranial recordings.
• Alarcón et al. JNNP 1994;57:435-49.
– Scalp/FOE or depth/subdural or
scalp/subdural/depth
– Mesial temporal focal spike voltage gradient ~
750μV/2.5mm
– Estimated depth current dipole 2 nA·m would
produce scalp voltage of 0.45μV
– A typical 100μV scalp spike would require a mesial
temporal focal dipole strength ~ 100-600 nA·m
(an 80 mV hippocampal spike!)
• Nayak et al. Clin Neurophysiol 2004;115:1423-35.
– Scalp/FOE
– Only 9% of temporal spikes seen intracranially
visible on scalp w/o averaging
*
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
750 uV
1 sec
RPT4-Ref
*
Comparison of intracranial ictal epileptiform activity recorded during sleep with simultaneous scalp EEG.
Focal electrographic seizure in right hippocampus (rhythmic activity at intracranial depth electrode contact RHD1) has no scalp
EEG correlate. Referential montage; reference = common average 10-20 electrodes. Top 16 channels = scalp EEG. Channels
17-20 and 21-24 = left and right, respectively, temporal depth electrode recordings. Sensitivity = 15μV/mm for scalp EEG, 50
μV/mm for intracranial recordings.
Intracranial EEG (ECoG)
Intracranial EEG of one mesial temporal lobe seizure (continuous recording from top left to bottom right).
EEG recorded from a depth electrode contact situated within the right anterior hippocampus in a patient
with medically-refractory temporal lobe epilepsy. Referential montage, scalp FCz reference.
Temporal lobe epilepsy
Left regional hippocampal/parahippocampal seizure onset
(Intracranial depth electrode recording)
Temporal lobe epilepsy
Seizure “spread” to right mesial temporal region
(Do seizures “spread” or “jump”?)
An individual patient may have more
than one morphology and/or
localization of seizure onset
Next seizures all from same patient, now seizure free
>1 year after right anterior temporal lobe resection
RHD1-Ref
750 uV
500 msec
RHD1-Ref
750 uV
500 msec
RHD1-Ref
750 uV
500 msec
LHD1-Ref
750 uV
500 msec
LHD1-Ref
750 uV
500 msec
Five different seizure onsets recorded from intracranial depth electrodes in one patient over 24 hours
RHD1-Ref
750 uV
500 msec
RHD1-Ref
750 uV
500 msec
RHD1-Ref
750 uV
500 msec
LHD1-Ref
750 uV
500 msec
LHD1-Ref
750 uV
500 msec
…Continuation of the five seizures from previous figure
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
Focal onset
Left Hippocampus
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
Regional onset
Left Hippocampus
Parahippocampus
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
Regional onset
Right Uncus
Hippocampus
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
Regional onset
Right Uncus
Hippocampus
“spread” to Generalized
RAT1-Ref
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
LHD1-Ref
LHD2-Ref
LHD3-Ref
LHD4-Ref
LAT1-Ref
LAT2-Ref
LAT3-Ref
LAT4-Ref
L.MT1-Ref
LMT2-Ref
LMT3-Ref
LMT4-Ref
LPT1-Ref
LPT2-Ref
LPT3-Ref
LPT4-Ref
RHD1-Ref
RHD2-Ref
RHD3-Ref
RHD4-Ref
RAT1-Ref
RAT2-Ref
RAT3-Ref
RAT4-Ref
RMT1-Ref
RMT2-Ref
RMT3-Ref
RMT4-Ref
RPT1-Ref
RPT2-Ref
RPT3-Ref
RPT4-Ref
Time
Intraoperative ECoG
Pre-resection ECoG in a patient with right temporal lobe epilepsy, hippocampal sclerosis and a posterior middle temporal gyrus gliotic lesion.
C1-4 inferior temporal gyrus, C4 anterior. C5-8 middle temporal gyrus, C8 anterior. C11-14 superior temporal gyrus; C1, C5 over lesion, C11
superior to lesion. C14-17 above Sylvian fissure. Propofol bolus given 3 minutes earlier with maximal activation of inferior temporal spikes.
ECoG 2 min after bolus of
alfentanil: activation of
amygdala/hippocampal
spikes and suppression of
temporal neocortical spikes
ECoG 10 min later: return
to pre-activation baseline
of amygdala/hippocampal
spikes and reappearance
of independent temporal
neocortical spikes