Background: Electroencephalography (EEG)

      In an Electroencephalogram, electrodes on the surface of the skin detect the electrical field caused by brain activity. Through recording electrodes in conductive media placed carefully on the head, an EEG selectively measures activity in specific brain regions. These methods are used to pinpoint sensory areas that respond specifically and predictably to brain-state activity and lend insight into the brain’s method for processing information from the environment.

       EEG recordings register the summed electrical activities of entire populations of neurons.[1] In fact, even though readings are typically on the order of magnitude of milli- or microvolts, each electrode detects the electrocellular activity of roughly a billion cortical neurons.[2] To accurately interpret the information this data reveals, a proper EEG setup must amplify the signal magnitude and filter out any interference buried in the recording. The complex signal that remains is typically isolated into narrow, pre-defined frequency bands that have been linked to specific brain activity. Spectral analysis, or determination of power spectral densities (PSD) identifies the frequency content of a signal through its distribution over frequency. [3]

 

 

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[1] Lopes da Silva F. EEG: origin and measurement. In: Mulert C, Lemieux L, eds. EEG-fMRI; 2010.

 

[2] Kaiser D. Basic principles of quantitative EEG. Journal of Adult Development 2005; 12(3)99-104.

 

[3] Dressler O, Schneider G, Stockmanns G, et al. Awareness and the EEG power spectrum: analysis of frequencies. British Journal of Anaesthesia 2004; 93(6)806-9.