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:
- AMPL – electrical height
- FREQ – no. times per sec wave touches zero voltage line
- TIME
- 4 waves
- β > 13Hz →awake, excited, alert, REM
- α 8 – 13Hz →awake, relaxed, quiet rest
- θ 4 – 8Hz →sleeping
- 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