K5ii: Describe the principles behind the electroencephalogram and evoked potentials

EEG – Electroencephalography

  • Recording of electrical activity of the brain
    • 20 reference electrodes
    • Anatomically placed
    • 20 lines graphed
    • Sum of thousands of post-synaptic potentials generate an electric current →recorded at the surface
    • Represents the voltage difference b/w 2 electrode locations
    • 3 parameters recorded:
      1. AMPL – electrical height
      2. FREQ – no. times per sec wave touches zero voltage line
      3. TIME
    • 4 waves
      1. β > 13Hz →awake, excited, alert, REM
      2. α 8 – 13Hz →awake, relaxed, quiet rest
      3. θ 4 – 8Hz →sleeping
      4. δ 0 – 4Hz →deep sleep, encephalopathy
    • EEG →records the electrical activity of millions of neurons →NON-SPECIFIC

Evoked Potentials: triggered →very specific

  • Evoked potentials = polyphasic waves produced after stimulation of specific neural tracts
  • They can detect slowed electrical conduction e. due to demyelination along pathways even when there is no clinical sign yet
  • e. MS diagnosis requires 2 distinct areas of demyelination ∴EP testing can confirm diagnosis