This document discusses different types of artifacts that can appear on an EEG, including how to identify and eliminate them. It separates artifacts into physiological artifacts originating from the patient's body (e.g. eye movements, muscle activity), and extraphysiological artifacts from external sources (e.g. electrodes, equipment, environment). Specific artifact types like blinks, lateral eye movements, muscle activity are described. Guidelines provided on how to reduce artifacts include closing the eyes, relaxing muscles, ensuring good electrode contact, and shielding from environmental interference.

1. Introduction:
• Unwanted electrical activity arising from
different sources, other than cerebral
activity
• EEG -highly sensitive recording device,
easily interrupted by other electrical activity
of very high voltages
• Some readily distinguished, others closely
resemble cerebral activity .

2. Principles used to discriminate
artifacts from EEG signals:
• Physiological activity has a logical
topographic field of distribution with an
expected fall off of voltage potentials.
• Artifacts have an illogical distribution that
defies the principles of localization

3. Classification:
• Physiological : from patient’s own
physiological generator sources other than
the brain
• Extraphysiological : Externally generated
e.g. instrumental & environmental

4. Physiological artifacts:
• Cardiogenic-electrical
mechanical
• Muscle activity
– Eye movement
– surface EMG
– Movement
glossokinetic
respiration
photomyoclonic
• Skin artifacts
perspiration
salt bridges
• Eye movements
Blink
flutter
Lateral gaze
Lateral rectus spike
Slow eye movements
Electroretinogram
REM sleep

5. Eye movement artifacts:
• most common, due to cornea-retinal potentials. The cornea is
positive to the retina by 50-100 mv
• Fp1, Fp2, F7, F8 , amplitude is approx 50- 200uv
• frontopolar rhythmic slow wave activity - simulating brain
activity
• Types of eye movement artifacts
– Eye open, eye closure and blink
– Eyelid flutter
– Eyeball movement (lateral, vertical and oblique
eye movements

6. Eye opening and eye closure

7. Blink
Eye blink is a “U” shape transient potential which appears in
frontopolar electrodes which are closer to the eyes.

8. Eyelid flutter
Fine eyelid movements may produce rhythmic 4-8 Hz activity in the
frontal leads (disappear on fixation)

9. Lateral eyeball movements

10. Elimination:
• close the eyes or eye fixation
• close his eyes with his fingers or place a
soft cloth or a cotton pads over the closed
eyelids
• Monitoring eye movements by placing
extraocular electrodes will easily help to
distinguish from frontal slow waves

11. Muscle (EMG) artifacts:
• EMG artifacts are due to the muscle contraction
superimposed upon the EEG activity
• The motor unit potentials (MUPs) arising from
the scalp muscles may cause misinterpretation by
resembling spike or cortical β-activity

12. Lateral rectus spikes:

13. Frontalis:

14. Temporalis:
Clenching and grinding teeth

15. Swallowing:
Swallowing of saliva usually produces a short burst activity

16. Chewing:

17. Sniffling artifact:
Small EMG component with a slow wave

18. Facial myokymia:

19. Glossokinetic artifact:
Movement of the tongue during speaking may produce synchronous
intermittent rhythmic EEG activity (2-6 Hz) because the mass of the
tongue acts as a charged body with a negative tip

20. Glossokinetic artifact:

21. Tremor:

22. Differentiation between EMG artifacts &
the cortical spikes:
• EMG potentials are of extremely short duration
(2-20 msec) and spiky even on increasing paper
speed to 60 mm/s
• On basis of morphology and frequency
• During sleep EMG activity is reduced whereas
cortical spikes increase
• Document using extra muscle electrodes

23. Reduction/elimination:
• Frontalis - close eyelids lightly and relax
• Temporalis - opening the mouth
• Use of relaxation techniques (reassuring,
comforting the patient),Massaging the particular
muscle groups
• Occipitalis - putting the pillow under the neck
• As a last resort change the high frequency filter to
35/15 Hz

24. Cardiogenic artifacts:
• EP arising in the cardiac muscles, high in amplitude
• Spread to scalp by volume conduction
• Prominent in babies, obese, short – neck, cardiomegaly
• Referential montage picks up ECG artifact due to large
interelectrode distances and close proximity of ear
electrodes to the heart
• Equipotential on the scalp - not picked up in bipolar
montage

25. Types:
• ECG
• Pulse
• Pacemaker

26. ECG
Coming at regular intervals synchronising with ECG

27. ECG:
Coming at regular intervals synchronising with ECG

28. Pulse

29. Pulse:

30. Elimination:
• Changing the head position relative to the
thorax
• Lower the electrode resistance (A1 and A2)
or use body earth (A1+A2)
• Change reference to Cz
• Shift the electrode a little - eliminate pulse
wave

31. Sweat artifact:
• Warm and humid recording room
• Anxiety and emotional tension
• Autonomic dysfunction
• Electrical potentials due to sweat glands
• Reduction in the skin resistance (GSR)
• NaCl and lactic acid of sweat may produce
large base line sways

32. Sweat:
These are the slow waves of very low frequency (1/3-1/2 Hz)

33. Salt bridge:
Electrolyte in sweat interact with electrode gel / paste to
produce a salt bridge

34. Elimination:
• Proper air conditioning
• Reducing emotional stress
• Sponging the patient’s face & forehead with
alcohol/spirit
• Setting the short time constant (LFF) if all the
efforts fail

35. Movement artifacts:
• Movement of head, body and limbs produce irregular
high voltage potentials
• Movement of the head during HV or respiration can
produce occipital electrode artifacts
• Movement associated with seizure may obscure
cerebral activity
• Artifacts may occur in essential tremors, Parkinson
disease and other movement disorders

36. Head movement:
Movement between the head and the pillow

37. Movement associated with seizure:
Contraction of skeletal muscles before the seizure activity starts

38. Movement associated with seizure:
Difficult to determine the origin of the seizure activity

39. Patting artifacts:
Mother patting baby

40. Respiration artifacts:
More commonly seen during HV as slow wave activity

41. Reduction/elimination:
• Solicit the co-operation of the patient to be calm
and still
• Changing the position or turning the patient over
will diminish tremor artifacts
• Placing a roll of towel or firm material under the
neck may do away with respiratory artifacts

42. Extra physiological artifacts:
– Electrode –electrode pop, contact
–Technical-lead movement, placement
–Instrumental –AC 60hz artifact
ventilator, circulatory pumps
–Iv fluids
– Environmental-mobile, TV, radio,
electromagnetic

43. • The scalp-electrode junction is an important and
delicate link in the whole system
• Electrode artifacts occur due to the change in the
resistance or electrode potential between the scalp
and the electrode
• Poor contact, improper electrolyte application,
broken lead, poor contact at the junction box, dry
out of electrode paste
Electrode artifacts:

44. Electrode pop:
A sudden change in the electrical potential between
the electrode and scalp gives rise to the ‘pop’

45. Electrode artifact:
Loose contact of the electrode with the scalp

46. Electrode movement artifact:
This is movement of electrode on the scalp, because of excessive jelly

47. Recognition & differentiation from cerebral activity:
• Electrode artifact is strictly confined to one lead or channels
having input from this electrode, where as cerebral activity
would usually spread to the adjacent electrodes
• In a bipolar montage, the artifacts show mirror images
(like phase reversals) in two adjacent channels
• Wave morphology may change from time to time
Electrode artifacts:

48. Elimination
• Applying proper electrolyte
• Check electrode impedance & continuity
• Change the electrode
• If it still present change the position at a
distance of 0.5-1cm
Electrode artifacts:

49. • due to the malfunctioning of certain parts of the machine
-Pen deflection
-Amplifier
-Galvanometer
-Faulty ground
-Photic stimulator
Instrumental:

50. • Non-symmetrical electrode placement
• Erroneous settings of different channels
• Unequal electrode impedances result in loss of
common mode rejection and recording of AC
artifact
Technical artifacts:

51. Pen deflection:

52. A1- disconnected:

53. Photic:

55. Interchanging electrode placement:
Interchanging the Fp2 electrode with O2

56. AC artifact:60 hz artifact
Very high electrode impedance of more than 25 kΩ

57. • troublesome as they cannot be easily controlled by the
technologist
• Movement of other persons
• Types of environmental artifacts:
– Electromagnetic Interference
– Electrostatic Induction
– Radio frequency Interference
• As technology expands – new artifacts appear
– Mobile phone artifacts
Environmental artifacts:

58. Electromagnetic interference:
• Current flowing through an electrical conductor (main
power supply), produces a magnetic lines of force around
the conductor
• The greater the current, the stronger the field
• Occurs between mains and patient or electrode attached to
the scalp or junction box
• Common sources – power transformers
– Electric motors in lifts, fans, air-conditioners
• AC interference (result of capacitance or inductive effects
on wires leading from the scalp to the junction box)

59. Electrostatic Induction:
• Opposite polarities of two charged bodies produces
electrostatic induction when negative electric charge is
applied
• Presence of several instruments adjacent to the EEG
machine (like fluorescent light, ventilators etc.)
• Movement of any charged body near the patient (like
plastic, rubber, synthetic fibres etc)
• Often the technologist himself is the recipient of this
discharge
• Low electrical resistance between patient and the
environment

60. Static artifact:
Produced by placing a charged synthetic paper near the patient

61. Static artifact:
walking in to collect a report

62. Electrostatic artifact:
Startle or clap response can also cause static artifact

63. AC Interference

64. Cell phone artifact:

65. Minimisation/removal of environmental artifacts:
• Keeping electrode leads close together.
• Move away from source (at least 10 feet)
(since electrostatic induction is inversely proportional to
the distance between patient and source)
• Changing the orientation of the patient/source parallel to
the electromagnetic lines of force
• Locate the EEG lab at least 50 feet away from AC
feeders, transformers etc.
• One earthing point common to all equipment
• Shielding the source of artifact and machine with earthed
metal shield

66. Artifacts are also useful:
• Slow lateral eye movements and disappearance or
reduction of EMG are a valuable sign of
drowsiness/sleep
• Eye open and eye closure artifacts record the precise
point where the patient opened or closed his eyes
• Short bursts of EMG activity may mark the occurrence
of myoclonic jerks

67. Environment for artifact free recording
• Quiet atmosphere
• Comfortable bed
• No synthetic carpeting
• Convenient control of lighting
• Proper earthing / shielding
• Different power supply to equipment and air
conditioner
• Comfortable temperature and humidity levels to
avoid sweating, tension, restlessness

68. Thank you