This document discusses artifacts and normal variants that may appear on EEG recordings. It describes various types of artifacts that can originate from patient physiology like eye movements, muscle activity, and heartbeats. It also discusses artifacts from external interference and equipment issues. Normal variants are described like alpha rhythm, sleep transients, and frontal rhythms seen in drowsiness that should not be mistaken for epileptiform activity. The document provides details on identifying features of each artifact and variant to differentiate them from cerebral abnormalities.

1. ARTIFACTS & NORMAL
VARIANTS
DR.SHAHANAZ AHAMED.M
PAEDIATRIC NEUROLOGIST
GMC,TVM

2. Artifacts
 Artifacts are pen deflections not caused by
cerebral activity.
 They may be due to
 1)physiological activity originating from the
patient
 2) Interference from power lines or other
electrical sources
 3)Malfunction of the recording system
which includes recording electrodes,
amplifiers, pen motors & paper drive.

3. Artifacts from patient
 Blinking & other eye movements
 Muscle artifacts
 Movement artifacts
 Heart beat artifacts
 Pulse wave artifact.
 Perspiration artifact
 oropharyngeal artifacts

4. Interference artifacts
 60 HzArtifact
 cardiac pacemaker artifact
 mobile phone artifact

5. Artifacts from Equipment
 Electrode poping
 Paper stop artifact
 Impedence artifact

6. ALPHA

8. EPILEPTIFORM TRANSIENTS
 SPIKES
 SHARP WAVES
 SLOW SHARP WAVES – not always
epileptiform

9. Blinking & other eye movements
 These are picked up by frontal electrodes
 Vertical eye movements cause potentials in
electrode pairs in paramedical positions-Fp1-
F3, Fp2-f4 etc
 Lateral eye movements  Deflections in
transverse chains=Fp1-F7, Fp2-F8, F7-F3
 F8-F4 etc

10.  Blinking or eye closure causes large down
going deflections,
 Eye opening produces upward deflections.

11. EYE BLINK

13. EYE OPENING

14. EYE CLOSURE

15. Lateral eye movements
 Lateral eye movements may be
preceded by a single sharp muscle
potential which may resemble a
cerebral spike & in combination with
eye movements form a spike & wave
artifact

16. LATERAL EYE MOVEMENTS

17. Eye movement artifacts
 Eye movement artifacts can be
identified by their
 frontal distribution,
 their symmetry on the 2 sides &
 their characteristic shape.

18.  Slow repetitive rhythmic eye
movements may closely resemble B/L
synchronous frontal slow waves like
FIRDA
 They are stopped by asking the patient
to place his fingertip on the
eyes,tapping cotton balls over the eyes
etc

19. Muscle artifacts
 Muscle activity causes very brief
potentials which usually recur.
 If they recur they resemble cerebral
discharges except that most cerebral
spikes are of much longer duration than
muscle potentials.
 Moreover epileptiform activity usually
has a aftercoming slow wave
associated with a spike.

20. MUSCLE ARTIFACT

22. MUSCLE ARTIFACT
 They are usually recorded
predominantly from frontal/ temporal
electrodes but can occur in any
electrodes
 They can be eliminated by asking the
patient to relax, drop the jaw or open
the mouth slightly/change position.
 Repetititive movements such as
chewing, blinking & tremor may give
rise to fast & slow artifacts which

23. Movement artifacts
 Movement of head /body or other
rhythmic movements such as chewing
& sucking can lead to irregular high
amplitude wave forms which can be
easily recognized.
 They do not have consistency &
characteristics of cerebral discharges
 They can occur in instances such as
restless/ confused patients,infants &
children , patients having

26. Heart beat artifacts
 Mainly in recording with wide
interelectrode distances& in subjects
with short necks.
 Small artifacts reflect mainly the Rwave
of ECG. Large artifacts may reflect
additional components of ecg

28. EKG ARTIFACT

29. Heart beat artifacts
 If necessary heart beat can be
eliminated by using a balanced
noncephalic reference.
 They can be identified by the equal
intervals & rate corresponding to heart
rate.
 Simultaneous recording of ecg can be
done in doubtful cases

30. Pulse wave artifact
 Periodic waves of smooth /triangular
shape may be picked up by electrode
on or near a scalp artery
 .More likely to occur in frontal/temporal
areas. It can be eliminated by
reapplying electrode

31. Perspiration artifact
 Sweating causes very slow drifting of
electrodes lasting several seconds .
 Usually common in frontal/temporal
electrodes & occurs in several channels
at the same time

32. Glossokinetic & oropharyngeal
artifacts.
 They produce intermittent /repetitive
slow waves in a wide distribuition often
with a maximum in the middle of the
head
 They occur in speaking, chewing,
swallowing
,sucking,coughing,hiccoughs.

33.  Palatal myoclonus causes rhythmical
artifacts at the rates of 100-200 /mt.
 Dental spike like artifacts are produced
by dental fillings /dissimilar metals
rubbing against each other

34. GLOSSOKINETIC ARTIFACT

35. Interference artifacts
 Artifacts due to electrical interference from
power lines & equipments.
 60 Hz is the frequency. Appears in all
channels.
 Other types of interference include signals
from nearby TV stations,
 radiopaging,Mobile phones
 telephone ringing,cardiac pacemakers,

38. CARDIAC PACEMAKER

39. mobile phone artifact
 Another confusing artifact is mobile
phone artifact which may look like a
epileptiform discharge but can be
distinguished by the lack of aftercoming
slow wave & positivity & raggedness of
the artifact wave

42. Artifacts from Equipment
 They are distinguished in that
 They differ radically from previously
recorded activity,
 Do not blend with other recorded
activity but seem to be superimposed
on it &
 Appear only in channels connected to
the faulty electrode.

43. Electrode poping
 Electrode poping is due to sudden
changes in electrode contact causing
spike artifact.

46. PAPER STOP ARTIFACT

47. A1/A2 ARTIFACT

48. NORMAL VARIANTS
 Hyperventilation changes
 Hypnagogic hypersynchrony
 Mu rhythm
 Lambda
 Positive occipital sharp transients of sleep(POSTS}
 Posterior slow waves
 Ctenoids/14 & 6hz positive spikes
 6 hz spike wave
 Rhythmic midtemporal theta-Psychomotor variant
 Small sharp spikes
 Frontal arousal rhythm

49. HYPERVENTILLATION
 HV produces bursts of 2—3 HZ
frontally dominant delta activity.
 Normal background in between.
 Can be admixed with sharper
components.

51. “ V” WAVES
VERTEX WAVES
 Bilaterally synchronous
 Maximum amplitude at vertex
 Extend to central, frontal & parietal
 May appear in sequence
 Shifting asymmetries may occur
 Higher amplitude in youth
 Principal component is sharply contoured
electronegative wave.
 Occurs in light sleep

53. Hypnagogic hypersynchrony
 Prominent bursts of rhythmic high
amplitude delta slowing maximum in the
parasagittal area are a normal finding in
the drowsy state in the first few years
of life

54. HYPNOGOGIC
HYPERSYNCHRONY
 Appears during transition from wakefulness
to drowsiness
 Seen in age group 5 months to 10 yrs.
 Bursts of 3-5 Hz , moderate to high
amplitude activity.
 Lasts for 1.5 to 3 secs.
 Can be mistaken for spike –wave
activity,when intermixed with faster
frequency components.

57. Mu rhythm
 It is a 7-11 hz saw tooth shaped rhythm
seen in 15 % recordings
 It can be unilateral/bilateral & seen in
central area
 It is attenuated by touch/ movement

59. Lambda
 Lambda is low amplitude (< 20micv)
sharp transient bi/triphasic activity
which is surface positive
 It is seen in the waking state due to
visual exploration & attenuated by
closing the eyes

62. POSTS
( Positive Occipital Sharp Transients of
sleep)
 Occur in NREM sleep ;Esp. stages - 2 & 3
 Occur in occipital region.
 Monophasic, sharp contoured, electropositive
waves.
 Similar to Lamda waves; higher in amplitude
& longer in duration.
 Occur singly or in trains of 4-6 Hz.
 Usually bisynchronous, but may be
asymmetric

63. POSTS
( Positive Occipital Sharp Transients of
sleep)
 Differentiating points from spikes:

Predominant phase is surface
positive

Monophasic

Occur in trains of 4-5 Hz.

Bilateral occurrence of POSTS

65. Posterior slow waves
 They are 1-4 hz slow waves seen
spreading from occipital to tremporal to
parietal which are prominent in first
decade.

67. Ctenoids/14 & 6hz positive
spikes
 Seen b/w 5-15 yrs in the posterior head
region as a surface positive comb
shaped rhythm

69. 6 hz spike wave
 It is a bisynchronous low amplitude
5-7hz spike wave rhythm most
prevalent in drowsiness & light
sleep.
 It is of gradual onset & offset &
maximal in midcentral/parietal
electrodes

71. Rhythmic midtemporal theta-
Psychomotor variant
 Theta rhythm of 5-7 hz seen in temporal
region unilateral/biateral lasting 5-10
seconds.
 Commonly seen in adoloscents.
Attenuated in stage 2 sleep & alerting

73. Small sharp spikes
 Medium amplitude spikes of short
duration seen in anterior & midtemporal
areas associated with drowsiness &
light sleep

75. Frontal arousal rhythm
 They are bursts of rhythmic notched
theta with superadded beta in
midfrontal regions on arising from
sleep,seen in 2-14 yrs lasts upto 20
sec.
 Can resemble ictal pattern. But there is
no evolution