Evoked Potentials

from Wikipedia, the free encyclopedia

Evoked potentials ( Latin evocare , "bring about", "cause" and potentia , "strength", "power") are potential differences in the electroencephalogram (EEG), which are triggered by stimulation of a sensory organ or peripheral nerve . In a broader sense, all specifically triggered electrical phenomena in the EEG can be understood as evoked potentials.


Every sensory stimulus triggers changes in electrical potential in the sensory areas of the cerebral cortex . These evoked potentials can only be detected with the usual technology with significantly smaller amplitudes than the spontaneously occurring EEG signal (1–15 µV instead of 50–100 µV). In order to be able to measure and represent the evoked activity, several realizations of an evoked potential are averaged . The EEG is regarded as a stochastic interference signal that is independent of the stimulus and whose mean value is zero, while the evoked potential of interest is temporally linked to the stimulus. It shows the same course after each stimulus. As a result of the repeated presentation of a stimulus and the averaging of the subsequent EEG segment, the stimulus-independent activity tends towards zero, while the stimulus-related evoked potential is added up. The number of realizations necessary in practice depends on the signal-to-noise ratio and is different depending on the sensory modality and physical characteristics. With a potential triggered by light flashes, around 50 stimuli are sufficient, while around 1000 to 2000 stimuli have to be presented to measure the early acoustic brainstem potentials.

The evaluation takes into account the shape of the wave, the wave height ( amplitude ) and the transit time ( latency ).


See also


  1. ^ Roche Lexicon Medicine, 5th edition (online version) Search termsomatosensorisch e. P.
  2. Pschyrembel Clinical Dictionary Version 2002 (electronic version of the 258th edition), under the headingPotentiale, somatosensibel evozierte