normal eeg

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1. Normal EEG Dr. Sachin Adukia Dr. Gopal Krishna Dash

2. Contents Introduction Descriptors of EEG activity Normal EEG (Wakeful adult) Normal Sleep EEG Benign or normal EEG variants Activation procedures

3. Brief History Vladimirovich (1912) first animal EEG study (dog) Cybulski (1914) first EEG recordings of induced seizures Berger (1924) first human EEG recordings 'invented' the term electroencephalogram (EEG) American EEG Society formed in 1947 Aserinsky & Kleitman (1953) first EEG recordings of REM sleep

4. Introduction What Electrical potential generated by summation of cortical nerve cell (Pyramidal cell) Exictatory and Inhibitory Postsynaptic Potential Not Action potential

5. Generator Thalamic pacemaker cells in nucleus reticularis Thalamocortical neurons stimulated excitatory impulses to cortex. Tracing EEG is difference in voltage between 2 recording electrodes plotted over time

6. EEG recording depends upon differential amplification: output - expressed as d/b 2 inputs in an electrode: called a channel. Typically, 21 or more channels in a montage Common average reference Each electrode is compared to avg signal from all other electrodes Those susceptible to artifact (Fp1, Fp2, O1, O2) are excluded Bipolar montage each channel consists of comparison of 2 adjacent electrodes Transverse bipolar Electrode pairs are arranged in a L-R pattern, starting in the front moving posteriorly AKA “coronal” montage

7. Basic descriptors Frequency Delta – Below 3.5 HZ ( 0.1-3.5Hz) Theta – 4 to & 7.5Hz Alpha – 8 to 13 Hz Beta –13 to 30 Hz Gamma – Greater than 30 Hz Amplitude- uV , peak to peak Spatial distribution Reactivity to different stimuli

8. Alpha Origin: thalamus, cortex and corticothalamic reverberating circuits Frequency of 8-13Hz During wakefulness Over posterior regions of the head. Amplitude < 50µV. Best seen with eyes closed and physical and mental relaxation. Attenuated by: Visual or mental effort, eye opening, alerting stimuli. Amplitude higher on the right. Morphology : rounded or sinusoidal. Spatial distribution: Posterior : Occipital, Parietal, posterior temporal.

9. Alpha Rhythm

10. Beating

11. 8 Hz - by age 3 progressively increases until 9-12 Hz is reached by adolescence V ery stable in an individual, rarely varying >0.5 Hz. With drowsiness may decrease by 1-2 Hz Difference >1 Hz between the two hemispheres is significant. Alpha reactivity Eye opening, sensory stimuli, mental activity

12. EYES CLOSED

13. EYES OPEN

14. EYES CLOSED

15. EYES CLOSED EYES CLOSED EYES OPEN

16. Beta Frequency - Over 13 Hz Upper beta range ~ gamma range 2 main types precentral type : predominantly anterior and central regions related to sensorimotor cortex functions, reacts to movement or touch. The generalized beta activity : induced or enhanced by drugs may attain amplitude over 25 microvolts Accentuates in Drowsiness and stage 1 sleep. Excess medication (BDZ & Barbiturate) Amplitude Assymetry ~ > 35% is abnormal Breach rhythm Localised increase in beta activity in skull defect areas.

17. Diffuse beta

18. Breach

19. Theta term Theta -Gray Walter, 1944, ? related to function of thalamus. Frequency between 4 – 8Hz. Amplitude below 15mV normal rhythm during drowsiness 4 months  8 years : predominance over fronto-central regions In adolescents: can occur over anterior head regions In adults: diffusely or over posterior head regions

20. Mu rhythm Wicket/comb rhythm <5% EEG: young adults 7-11Hz For few seconds in central or centroparietal area Intermittent & asymmetrical : persistent asymmetry on same side is abnormal Accentuate: scanning visual images. Attenuate ~ voluntary/ reflex/passive movement/intention to move /tactile stimuli Physiological significance Somatosensory process associated with movement.

21. Pre discharge

22. discharge

23. discharge

24. Post discharge

25. Posterior slow waves of youth During awake state Notched broad (slow) waves Notching d/t merging of normal alpha waves in wakefulness Can be confused with epileptiform discharges

26. Like Alpha, post slow waves attenuate with eye opening

27. Reappear with eye closure

28. Normal sleep EEG (adults) Elements of normal sleep activity Slow waves Positive occipital sharp transients Vertex sharp transients Sleep spindles K complexes Sleep stages Drowsiness II Light sleep III Deep sleep IV Very deep sleep Sleep cycle

29. Stage 1 In adults, most sensitive sign of drowsiness is the disappearance of eye blinks and slow eye movements Slowing , dropout or attenuation of the background O ccurrence of theta activity over posterior regions

30. Just before sleep

31. Deep Drowsiness Vertex waves Maximum at the vertex. Young adults- sharp or spiky appearance , high voltages Older adults - more blunted appearance may be asymmetrical Physiologic , not to mistake for epileptiform activity Sometimes trains or short repetitive series, clusters, or bursts of in quick succession

32. Vertex waves may be asymmetrical

33. Stage 2 Positive Occipital Sharp Transients of Sleep (POSTS) S harp-contoured , monophasic , surface-positive transients single or in trains of 4-5 Hz over occipital regions S imilar appearance to lambda waves of awake record U sually bilaterally synchronous, may be asymmetric P redominantly during drowsiness and light sleep

34. Sleep spindles frequency of 13- 14 Hz symmetric and synchronous at intervals of 5-15 seconds S pindle trains ranging from 0.5-1.5 sec duration prolonged trains or continuous spindle ? Medication: BZP

35. K- complex B road diphasic or polyphasic waveform (>500 msec ) Seen in Stage II, III, IV NREM sleep. Frontal and central region Initial sharp component f/b slow component. Sharp component is biphasic. Slow component represented by large waves followed by superimposed spindles representing fast component. can occur in response to afferent stimulation and may be linked to an arousal response

36. Stage 3 Background activity shows delta frequency (0.7-3Hz). Rhythmic 5-9Hz low voltage activity. Sleep spindles- less prominent K complexes

37. Stage 4 rarely obtained in routine office EEG Prominent Delta activity. Sleep spindles and K complexes are rare

38. Sleep Cycle Each cycle contains all stages NREM & REM: 4-7 cycles /sleep 1 st cycle shortest: later 80-120 min. : REM sleep ~ appears 70-90 min after onset of sleep. Young adults: stage 1 5-10% stage 2 30-50% stage 3&4 20-40%

39. Benign discharges:- Transients and rhythms

40. BSSS- Benign spordic sleep spikes

41. Wicket Spikes

42. Pre discharge

43. discharge

44. Post discharge

45. 14 and 6 spike waves

46. Pre discharge

47. discharge

48. Post discharge

49. RMTD- Rhythmic mid-temporal theta discharges

50. Pre discharge

51. discharge

52. Post discharge

53. SREDA Subclinical Rhythmic Electrographic Discharge Of Adults

54. Pre discharge

55. discharge

56. discharge

57. discharge

58. Post discharge

59. Hypersynchronous hypnogogia

60. Pre discharge

61. discharge

62. Post discharge

63. discharge

64. Hyperventilation O ften produces little change in the EEG in adult If there is a change, usually consists of generalized slowing. either gradual or abrupt onset in theta or delta range may continue as series of rhythmic slow waves or consist of repeated bursts of slow waves at irregular intervals

65. Pre discharge

66. discharge

67. Post discharge

68. discharge

69. Photic stimulation Driving response- posterior , time locked to stimulus Photo- myoclonic resonse electrical activity of frontal scalp muscles- Frontalis and Orb Oculi Repeated contractions of these musc . produces time locked response Anterior Same freq as the flash

70. References Abou-Khalil B, Misulis KE. Atlas of EEG & seizure semiology : Text with DVD. Butterworth-Heinemann; 2005 Oct 12. Laoprasert P. Atlas of pediatric EEG. McGraw Hill Professional; 2010 Dec 31.

71. Thank You