EEG- CONCEPTS AND CLINICAL USES FOR NEUROLOGY RESIDENTS

EEG- CONCEPTS AND CLINICAL USES FOR NEUROLOGY RESIDENTS

1. Fundamentals of an EEG - Dr. Aayam Adhikari Medical Officer

2. History of an EEG 1875- English scientist Richart Caton observed these EEG signals from the exposed brains of rabbits and monkeys. 1924- German Physician Hans Berger used ordinary radio equipment to amplify electrical activities in the human brain. He lead s the foundations of modern electroencephalography. 1934- Adrian and Matthew published a paper on “ human brain waves “ and identified 10-12 Hz frequency and termed them “ alpha rhythm “

3. Tribute to Hans Berger

4. Introduction EEG is defined as an electrical activity of an alternating type recorded from a scalp surface after being picked up by metal electrodes and conductive media. It is a non-invasive diagnostic tool with minimum harm/side effects. It measures mostly currents that flow during synaptic excitation of pyramidal neurons in the cerebral cortex.

5. Introduction Electrocorticogram- EEG measured directly from the cortical surface. Electrogram- EEG measured directly from depth probes.

6. Resting and action potentials The r esting membrane potential is -70mv.

7. The action Potential

8. Organisation of Cerebral Cortex

9. Complex architecture of Neural elements Inhibitory and excitatory are spatially segregated over the surface of these neurons. Oriented vertical to the Cortical surface.

10. Direction of current flow reflects polarization due to EPSP or IPSP

11. EEG is a measure of Neural Synchrony The p otential produced by a single neuron is too small to be measured by an electrode placed o n the scalp. Since they are vertically oriented, they can SUMMATE . EEG is produced from a MASSIVE number of neurons, approximately 100000 neurons.

12. Neurons as electrical Dipole Potential differences can be measured between electrodes located at different iso-potential lines. Dipoles perpendicular to the scalp is picked up by the electrodes while the parallel/tangential ones are not.

13. Rules of Polarity POSITIVE Is DOWN . Negative potentials are upgoing waves and positive potentials are downgoing waves. EEG OUTPUT IS ALWAYS RELATIVE !!!!

14. Non invasive measurement of EEG International 10-20 system- consistent naming and reproducible placement. Reference points- Nasion, Inion, Left and right pre-auricular points. Locations- F-frontal, T-temporal, P-parietal, O-occipital and z- central Numbers- Even- right side, Odd- left side

15. Anatomical landmarks

16. Nomenclature of Electrode placement

17. Bipolar Montage

18. Bipolar Montages

19. Phase reversal Significance : 1. Negative phase reversals are normally seen over epileptiform discharges

20. Field Reversal

21. End of Chain Phenomenon In a bipolar montage, for the first and the last electrode in the chain, there is not an electrode in front to compare to and this give rise to end of chain phenomenon.

22. Circumferential Montage They do not have para-sagittal electrodes. This array of electrodes are only used to screen particular area of concern.

23. Referential Montages

24. An example of EEG

25. Brain waves classifications : Beta waves ( more than 13 Hz ) Alpha waves ( 8-13 Hz). Theta waves (4-8 Hz) Delta waves (0.5-4 Hz )

26. Different waves and frequencies at different areas of the brain

27. Waveforms Alpha waves are one of the most studied waveforms. They are normally found in the posterior and occipital regions. It is induced by sleep, relaxation, or alertness in the form of thinking and calculation. Beta waveforms are more dominant during the state of wakefulness with open eyes. If sleep occurs, the lower frequencies of waveforms are seen. Individual state of mind and their thinking abilities can alter the waveform patterns.

28. EEG Description Frequency Location Morphology – Amplitude and Rhythm ( polymorphic or rhythmic)

29. EEG MORPHOLOGY

30. SYSTEMATIC EEG READING State : Sleep, Awake , Drowsy Normal background or slow Symmetry and focal slowing Epileptiform activity Artifact

31. EEG AWAKE

32. EEG features of wakefulness Myogenic artifacts. Posterior dominant Rhythm ( alpha wave ) Eye movements ( eye blink ) Alpha blocked with open eye.

33. Muscle artifacts

34. EEG features of Drowsiness Decreased muscle artifact. Slow rolling eye movements. Loss of alpha waves Increased Theta wave activity.

35. EEG- Drowsy Roving eye movements Less muscle artifact Less muscle activity

36. Alpha waves Look at the differences of the activity of alpha wave on eye opening and closure- reactivity Frequency- 11 Hz Amplitude- 40-50 MV S ometimes alpha waves are called POSTERIOR DOMINANT RHYTHM

37. Interpreting the Alpha Rhythm

38. Interpreting the Alpha Rhythm

39. Posterior Dominant rhythm It is the resting rhythm in the posterior region once the eyes are closed and the patient is quiet. PDR should be symmetrical in frequency and amplitude. A normal PDR is 8.5-12Hz. Abnormal if there are 50% changes in the amplitude and 1 Hz change in the frequency.

40. Varients of Alpha waves Alpha squeak- transient increase in frequency before the alpha waves reach a stable 11 Hz frequency. Myogenic muscle artifact Lambda waves Mu Rhythm

41. Mu rhythm Arch shape Produced by the somatomotor cortex

42. EEG in Sleep Posterior Occipital Sharp Transient of Sleep ( POSTS ) Absence of myogenic artifacts. No posterior dominant rhythm. Vertex waves ( late stage I and stage II sleep )

43. STAGE-I SLEEP

44. STAGE II SLEEP

45. Stage II Sleep K complex Sleep spindles

46. K complex High voltage Broad contour 2 or more phases S uperimposed fast activity. Occurs during arousals

47. Sleep spindles Present over the midline electrodes. Medium voltage Frequency- 11-15 Hz

48. STAGE II SLEEP K complex

49. Slow wave sleep Deep stage sleep. High voltage Delta Activity.

50. REM Sleep No normal alpha rhythm. No muscle artifact. Rapid, chaotic, complicated eye movements.

51. Epileptiform Discharges Occurs over cortical hyperactivity Sharp is a single epileptiform discharge defined by a duration of 7—200 ms and by its disruption of the EEG background. Spike ha s a shorter duration than spike, 20-70ms Multiple phases. Disrupt Background After coming slow wave. Lateralized periodic discharge- sharp and spike waves at periodic interval s and almost epileptogenic. It requires structural co-relation.

52. Epileptiform Discharges

53. Epileptiform Discharges

54. FOCAL SLOWING Focal cerebral dysfunction Brain Tumor Stroke Hemorrhage

55. While describing a focal slowing Location Frequency- delta and theta or mixed waves Continuous/ intermittent Rhythmic/ Polymorphic

56. Attenuation of fast activity on the left side

57. Breach Artifact In a thick skull, high frequency waves do not pass through

58. Breach artifact

59. Seizures Abnormal, organized, and evolving burst of cortical activity that interrupts the brain’s usual function. Organized and Evolving. Lasting more than 10 seconds. Epileptiform discharges aver a ging more than 2.5 Hz.

60. Seizures Evolution in terms of Morphology, Frequency and Location Frequency- 2 sequential change of at least 0.5hz ( each frequency lasting for 3 cycles at least ) Morphology- 2 sequential change to a novel morphology. Location- 2 sequential changes to a new electrode position.

61. EEG in Seizures - 1.Generalized seizures

62. Focal seizures

63. Focal seizure- strip II

64. Triphasic waves S een in Metabolic derangements

65. Artifacts in EEG 1. Eye blinks 2. Lateral eye movement 3. Chewing/mastication 4. Cardiac artifacts 5. Sweat 5. Artery pulsation

66. References Jeremy Moeller- https://www.youtube.com/watch?v=NY_CthbqObA&list=PLxaiR6teSdjoEZWaDWm28A9QjFN7eguAp&index=16 https://www.learningeeg.com/ https://www.louisvillelectures.org/neurology ( University of Louisville, Kentucky, USA )