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EEG: Basics

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EEG: Basics

  1. 1. Dr.M.Arivumani
  2. 2. EEG 1
  3. 3. EEG2
  4. 4. EEG 3
  5. 5. EEG 4
  6. 6. EEG 5
  7. 7. Function of EEG <ul><li>The EEG uses highly conductive silver electrodes coated with silver-chloride and gold cup electrodes to obtain accurate measures… use impedance device to measure effectiveness, resistance caused by dura mater, cerebrospinal fluid, and skull bone </li></ul><ul><li>Monopolar Technique : the use of one active recording electrode placed on area of interest, a reference electrode in an inactive area, and a ground </li></ul><ul><li>Bipolar Technique : the use of two active electrodes on areas of interest </li></ul><ul><li>Measures brain waves (graphs voltage over time) through electrodes by using the summation of many action potentials sent by neurons in brain. Measured amplitudes are lessened with electrodes on surface of skin compared to electrocorticogram </li></ul>
  8. 8. Sodium-Potassium Pump <ul><li>The mechanism within neurons that creates action potentials through the exchange between sodium and potassium ions in and out of the cell </li></ul><ul><li>Adenosine Triphosphate (ATP) provides energy for proteins to pump 300 sodium ions per second out of the cell while simultaneously pumping 200 potassium ions per second into the cell (concentration gradient) </li></ul><ul><li>Thus making the outside of the cell more positively charged and the neuron negatively charged </li></ul><ul><li>This rapid ionic movement causes the release of action potentials </li></ul>
  9. 9. History <ul><li>Richard Caton (1875) –localization of sensory functions with monkeys and rabbits </li></ul><ul><li>Hans Berger (1924) – first EEG recording done on humans - described alpha wave rhythm and its suppression compared to beta waves </li></ul><ul><li>- acknowledged “alpha blockade” when subject opens eyes </li></ul><ul><li>William Grey Walter – influenced by Pavlov and Berger, further developed EEG to discover delta waves during sleep (1937) and theta waves (1953) </li></ul>
  10. 10. Alpha Wave <ul><li>Characteristics: - frequency: 8-13 Hz -amplitude: 20-60 µV </li></ul><ul><li>Easily produced when quietly sitting in relaxed position with eyes closed (few people have trouble producing alpha waves) </li></ul><ul><li>Alpha blockade occurs with mental activity -exceptions found by Shaw(1996) in the case of mental arithmetic, archery, and golf putting </li></ul>
  11. 11. Alpha
  12. 12. Beta Waves <ul><li>Characteristics: -frequency: 14-30 Hz -amplitude: 2-20 µV </li></ul><ul><li>The most common form of brain waves. Are present during mental thought and activity </li></ul>
  13. 13. Beta
  14. 14. Theta Waves <ul><li>Characteristics: -frequency: 4-7Hz -amplitude: 20-100µV </li></ul><ul><li>Believed to be more common in children than adults </li></ul><ul><li>Walter Study (1952) found these waves to be related to displeasure, pleasure, and drowsiness </li></ul><ul><li>Maulsby (1971) found theta waves with amplitudes of 100µV in babies feeding </li></ul>
  15. 15. Delta Waves <ul><li>Characteristics: -frequency: .5-3.5 Hz -amplitude: 20-200µV </li></ul><ul><li>Found during periods of deep sleep in most people </li></ul><ul><li>Characterized by very irregular and slow wave patterns </li></ul><ul><li>Also useful in detecting tumors and abnormal brain behaviors </li></ul>
  16. 16. Gamma Waves <ul><li>Characteristics: -frequency: 36-44Hz -amplitude: 3-5µV </li></ul><ul><li>Occur with sudden sensory stimuli </li></ul>
  17. 17. Less Common Waves <ul><li>Kappa Waves: -frequency: 10Hz -occurred in 30% of subjects while thinking in Kennedy et al.(1948) </li></ul><ul><li>Lambda Waves: -amplitude: 20-50µV -last 250 msec, related to response of shifting visual image -triangular in shape </li></ul><ul><li>Mu Waves: -frequency: 8-13Hz -sharp peeks with rounded negative portions (7% of population) </li></ul>
  18. 18. <ul><li>Sleep and The EEG </li></ul>
  19. 19. Sleep and EEG cont’d: <ul><li>Different stages of sleep and their respective brain waves: </li></ul><ul><ul><li>Stage 1: Low voltage random EEG activity (2-7 Hz) </li></ul></ul><ul><ul><li>Stage 2: Irregular EEG pattern/negative-positive spikes (12- to 14- Hz) </li></ul></ul><ul><ul><ul><ul><li>Also characterized with sleep spindle and K-complexes that could occur every few seconds. </li></ul></ul></ul></ul><ul><ul><li>Stage 3: Alternative fast activity, low/high voltage waves and high amplitude delta waves or slow waves (2 Hz or less). </li></ul></ul><ul><ul><li>Stage 4: Delta waves </li></ul></ul><ul><ul><li>Stage REM (Rapid eye Movement): “episodic rapid eye movements,” low v voltage activity. </li></ul></ul><ul><ul><li>Stage NREM: All stage combined, but not including REM or stages that may contain REM. </li></ul></ul><ul><li>The K-complex occurs randomly in stage 2 and stage 3 </li></ul><ul><ul><li>The K complex is like an awaken state of mind in that is associated with a response to a stimulus that one would experience while awake. </li></ul></ul>
  20. 20. EEG brain waves in the Sleep Cycle:
  21. 21. Position of electrodes
  22. 22. A1-lefrt ear A2-right ear Fp-frontal pole leads F-frontal leads P-parietal leads C-central leads T-temporal leads O-occipital leads
  23. 23. Spikes and slow wave copmlexes- typical- 3/sec-absence seizures fast - 4-6/sec-myoclonic jerks slow -1-2.5/sec-intractable epilepsy with MR
  24. 24. Polyspikes –these rapid Polyspikes are found in GTCS Post traumatic epilepsy Lennox gastaut syndrome
  25. 25. INDICATION <ul><li>Epilepsy-diagnosis,classify,monitoring response to treatment,predicting prognosis </li></ul><ul><li>Comatose and confused patients </li></ul><ul><li>Non neurological disorder </li></ul><ul><li>Degenerative disease </li></ul><ul><li>Psychological and behavioural problems </li></ul>
  26. 26. EEG 1
  27. 27. Fast Spike and wave complexes GTCS
  28. 28. EEG 2
  29. 29. Repitive Spike on left side-right sided partial seizure
  30. 30. EEG 3
  31. 31. Spike and slow wave complex 3/sec absence seizure
  32. 33. EEG 4
  33. 34. High voltage delta activity-deeply comatose patient
  34. 35. EEG 6
  35. 36. SSPE- Periodic discharges at 4 sec interval. Maximum at fronto central areas Giant slow waves mixed with several sharp waves
  36. 37. <ul><li>REFERENCES </li></ul><ul><li>CLINICAL ENCEPHALOGRAPHY-U K MISRA </li></ul><ul><li>J KALTIA </li></ul><ul><li>THANK YOU </li></ul>