This presentation explains the technique, interpretation and utility of commonly used activation procedures in EEG.

1. Activation Procedures in EEG
Dr Pramod Krishnan
Consultant Neurologist and Epileptologist
HOD Neurology
Manipal Hospital, Bengaluru

2. Activation procedures
• These are specific manoeuvres performed during the EEG recording to
bring forth abnormalities that would not be seen otherwise.

3. Activation procedures used in EEG
Routinely performed activation procedures
1. Eye opening and Closure
2. Mental alerting
3. Intermittent photic stimulation
4. Hyperventilation
5. Sleep.
Activation procedures performed in special situations
1. Scotosensitivity and Fixation off sensitivity
2. Cognitive tasks like arithmetic, problem solving, playing chess etc.
3. Pattern stimulation
4. Television and video games
5. Eating
6. Reading
7. Praxis
8. Hot water bath

4. Eye opening and closure

5. Eye opening (negative deflection in Fp1 and Fp2) causing synchronous attenuation of posterior dominant
alpha rhythm. Eye closure (positive deflection in Fp1 and Fp2) results in return of alpha rhythm.

6. Manoeuvre Description
Eye closure sensitivity Generalised spikes occur immediately on eye closure and can last upto
4 sec. Eg Jeavons syndrome (classical), JME, JAE, IOE
Eye closed sensitivity Generalised or focal spikes occur only when eyes remain closed.
Disappear on eye opening. Eg. Childhood epilepsy with occipital
paroxysms.
Scotosensitivity Generalised spikes occur only in complete darkness, irrespective of
eyes being open or closed.
Fixation off sensitivity Generalised spikes occur when fixation is impaired. Eg using Frentzel
glasses.

7. Eye closed sensitivity: On eye closure repetitive generalised spike and waves are seen which continue for
several seconds unlike eye closure sensitivity where it does not last more than 4 sec.

8. Eye closed sensitivity: On eye opening, the spikes abruptly terminate. This pattern is most commonly seen
in idiopathic occipital lobe epilepsies. Eg Childhood epilepsy with occipital paroxysms.

10. Fixation off sensitivity: This patient has eye closed sensitivity (top left), possibly fixation off sensitivity or
scotosensitivity (top right, bottom left), only fixation off sensitivity (bottom right)

11. Mental alerting

12. Arithmetic calculation
• This is done with eyes closed.
• In an alert patient, mental activities like calculation cause attenuation
of the posterior alpha rhythm.
• In drowsy patients, mental activities increase the frequency of the
posterior dominant rhythm.
• If the background rhythm does not show increase in frequency on
alerting, it may be pathological slowing.

13. Mental arithmetic with eyes closed causes attenuation of the posterior alpha rhythm, which returns on
completion of the calculation task.

14. Intermittent photic stimulation

15. Intermittent photic stimulation
• Subject is asked to look at a series of flashing lights of different
frequencies ranging from 1 Hz to 50 Hz.
• Light source should be 30 cm away.
• Each frequency is delivered for 10 sec, which includes eyes open, eyes
closed and eye closing states.
• There is 10 sec gap between different frequencies.
• The sequence is 1, 3, 6, 8, 10, 12,14, 16, 18, 20, followed by 50, 40, 30, 24
and below.
• Red colored light and patterned IPS facilitate induction of PPR.

16. 1. Photomyogenic response

17. Photomyogenic artifact: Repetitive EMG artifacts that occur from facial muscles during photic stimulation.
They have a spike like morphology and are time locked to the photic flash.

18. Photomyogenic artifact: They lack after coming slow wave. They occur across all frequencies. They are
mainly seen over the frontal regions, and are bilateral. They do not occur beyond the photic stimulation.

19. Photomyogenic artifact: They occur with eyes open or closed.

22. 2. Photic driving

23. Photic drive: They are monophasic transients seen over the occipital regions, and follow each flash by
a lag of 80-150 msec, at the same frequency, or sub- or supra harmonically.

24. Photic drive: The occipital transients are time locked to the stimulus.

26. Ocular flutter: These are seen as rhythmic high amplitude deflections over the bifrontal regions that
resemble large amplitude delta waves.

27. 3. Photo-paroxysmal response

28. Photo-paroxysmal response
• PPR is defined as occurrence of generalised spikes/ polyspikes at least
twice during the same frequency of IPS, irrespective of the duration of
the paroxysm, or whether it outlasted the paroxysm or not.
• IPS must be discontinued if PPR is seen.
• Stimulus frequency at which PPR most frequently occurs is 15-18 Hz.
• It is more prevalent in females, and in those between 5-20 years of age.
• The photosensitivity range may be determined by stimulating the
ascending and descending frequencies.
• PPR has a high correlation with clinical epilepsy.

29. Photo-paroxysmal response
• Prevalence in a cohort of 575 epilepsy patients from South India was 3.5%.
• PPR was highest in PME (67%), JME (22%), other IGE (3%). About 15% of
patients with focal epilepsy can have PPR.
• Photosensitivity can be familial. Nearly one-third of siblings of epilepsy
patients with PPR may exhibit photosensitivity.
Grade Description
Grade 1 Spikes confined to occipital region.
Grade 2 Spikes confined to parieto-occipital region.
Grade 3 Parieto-occipital spikes extending to frontal regions.
Grade 4 Generalised spikes/ polyspikes.

30. Grade 3 PPR (longitudinal bipolar montage): Parieto-occipital spikes extending to frontal regions, seen
consistently at 12 Hz, in a patient with JAE.

31. Grade 4 PPR (longitudinal bipolar montage): Generalised spikes/ polyspikes and waves were seen
consistently at a frequency of 8Hz in a patient with JME.

32. Grade 4 PPR (average referential montage): Generalised spikes/ polyspikes and waves were seen
consistently at a frequency of 8Hz in a patient with JME.

33. Grade 4 PPR (longitudinal bipolar montage): Generalised spikes/ polyspikes and waves were seen
consistently at a frequency of 16 Hz in a patient with JME.

34. PPR
EEG bipolar montage showing rhythmic frontally dominant generalised spike and dome activity triggered by
photic stimulation at 10Hz, in aptient with CAE.

35. EEG referential montage showing the same findings.

36. Hyperventilation

37. Hyperventilation
• Breathe deeply at 20-30 breaths/ min for 3 minutes with eyes closed.
• Post HV observation should be for 3 minutes.
• Best seen in children between 8-12 years of age.
• Most prominent if blood glucose is below 80 mg/dl
• HV related changes diminish with age and is therefore not routinely
performed after age of 50 years.
• It should not be performed in patients with cardiovascular,
cerebrovascular or chronic lung diseases.

38. Abnormal slowing in HV
• Slowing can persist upto 1 min after cessation of HV.
• Focal slowing during HV may indicate an underlying pathology only if
it is also evident in the baseline EEG.
• Focal slowing only during HV should be interpreted with caution.

39. Hyperventilation
Washout of CO2
Respiratory alkalosis
Cerebral
vasoconstriction
Reduced cerebral
blood flow

40. Hyperventilation: Initially there is diffuse slowing in the theta range, followed by high amplitude 1.5-4Hz
delta activity, called ‘build-up’.

41. Hyperventilation: Initial diffuse theta is followed by delta range slowing which is symmetrical and
synchronous, more in the anterior region in adults and post region in children.

42. Hyperventilation: hyperventilation induced high amplitude rhythmic slowing (HIHARS) is a
hypersynchronous slowing seen in children during HV and may be confused with absence seizures
because of intermixed fast activity that may mimic spikes.

43. Hyperventilation: can accentuate asymmetrical or focal pathological slowing. Here the asymmetry between
the left and the right is accentuated during hyperventilation.

44. Hyperventilation: can accentuate asymmetrical or focal pathological slowing. Here the asymmetry between
the left and the right is accentuated during hyperventilation.

45. Hyperventilation: can trigger spikes in epilepsy patients. This EEG shows bifrontal spikes noted during
hyperventilation. Spikes are followed by delta range slowing.

46. Hyperventilation: Predominantly right frontal spikes are seen in this record during hyperventilation.

47. Hyperventilation: Frontally dominant generalised spike and wave discharges are noted in a patient with
JME during hyperventilation

48. HV
EEG bipolar montage showing rhythmic frontally dominant generalised spike and dome triggered by
hyperventilation.

49. EEG referential montage showing the discharges during hyperventilation.

50. Sleep

51. Sleep
• It is a powerful activator of nearly all forms of epilepsy.
• Routine EEG should include 20 min of awake and 20 min of sleep.
• Sleep deprivation can be used to obtain a sleep record. Patient is asked
to sleep 50% of his usual sleep time on the night prior to the recording.
• In children, Chloral hydrate (max 25 mg/kg) or Melatonin can be used
to induce sleep without significant drug induced alterations in the
EEG.

52. Referential montage showing frontally dominant generalised polyspike and wave discharges in a
22 year old patient with JME. Few focal frontal spikes are seen.

53. EEG bipolar montage: shows frontally dominant generalised polyspike and wave discharges
in sleep.

54. Longitudinal bipolar montage in a child with atypical BRE showing marked activation of spikes
in sleep, producing continuous spike and wave discharges in sleep.

55. Longitudinal bipolar montage in a child with LKS showing marked activation of spikes in sleep,
producing continuous spike and wave discharges in sleep.

56. MAMATA BAG(4714636)
Right and left frontal and fronto-temporal epileptiform discharges.
EEG Longitudinal bipolar montage of a 38 year old lady showing right fronto-temporal
spikes. MRI brain showed right fronto-temporal venous infarct.

57. Longitudinal bipolar montage of a 9 year old child with idiopathic occipital epilepsy showing
frequent occipital spikes in sleep on both sides.

58. Referential montage of a 5 year old boy showing frequent spikes in the central, parietal and
temporal channels, with phase reversal.

59. Referential montage of the same child showing marked activation of the spikes in sleep, which is
highly characteristic of BCECTS.

60. Special forms of stimulation
Watching TV Watch black and white TV at 2-3 m, and progressively reduce the distance to
30 cm. 40% of patients with PPR have seizures while watching TV. PPR may
occur only at high frequencies like 100 Hz.
Pattern sensitivity Invariably associated with photosensitivity. Isolated pattern sensitivity is
rare. Show a card of 30 cm width with alternating black and white stripes of
25 mm each at a distance of 50 cm from the eyes.
Somatosensory
stimulation
Touch, vibration may elicit myoclonus.
Lous sudden sound May elicit myoclonus or seizures in some.
Reading Silent and loud reading
Cognitive tasks Mental arithmetic, argumentative conversation, card or chess playing,
praxis.

61. THANK YOU