The ability to record EEG is dependent on the synchronization of the pyramidal cells that make up layers III or V of the cerebral cortex.


Frequencies are cycles per second, of any activity.  The period of one cycle typically measures in msec.


Frequencies are analyzed when they are separated out, individual wave form frequency form raw continuous EEG.

Evaluate the power and/or amplitude of identified frequency  – done by an FFT (fast fourier transformer)

  • Fournier Theorem – any physical function that varies periodically with time with a frequency (f) can be expressed as a superposition of sinusoidal components of frequencies: f, 2f, 3f, etc.
  • FFT is a specialized math function that generates a graph able numeric data of frequency in Hz by power.  This is known as spectral analysis, it can be represented by a line (CSA) or a colored graph (DSA)

Compressed Spectral Array (CSA)

  • Frequency is depicted along the X-axis
  • Power and Time along the Y-axis
  • Each line represents a chunk of analyzed processed EEG

eeg_csa_screen

Density Spectral Array (DSA)

  • Frequency is depicted by the X-axis
  • Power and Time along the Y-axis, but instead of lines, power is scaled by the color graph

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  • Increased values represented as red
  • Low values represented as blue
  • Yellow line is defined as the spectral edge
    • The spectral edge frequency (SEF) is the frequency that x % of the power and frequency are below that line (x is typically between 75-95%)
    • During CEA surgeries the SEF is usually set to 90-97%
  • Bispectral analysis is information on the phase coupling between frequencies in the EEG signal

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