Acoustically evoked potentials

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In the medical sense, acoustic evoked potential (AEP) is a change in the electroencephalogram (EEG) that is caused (“evoked”) by a sound event. Physically, AEPe are potential differences between different lead electrodes on the scalp, the time course of which shows a typical pattern for the respective measurement situation, which can be changed by diseases. The triggering sound event is called a “stimulus” and synchronizes the generally asynchronous activity of the inner ear (“ cochlea ”), auditory pathway and primary auditory center / cerebral cortex . The acoustic stimulus is presented to the test person via headphones or loudspeakers.

The AEP are a subgroup of evoked potentials .

Lead, electrode position

The strongest AEP is obtained when the active tissue from the cochlea to the auditory cortex is between the lead electrodes. Typically, one electrode is placed directly on the head (“Vertex”, Cz in the 10-20 system ) and one behind the right or left ear (“Mastoid”, A1 / A2). A third electrode is used as a reference (“ ground ”) and is usually attached to the forehead or neck. Due to the low signal strength of the AEP, the measurement is repeated several times and the measured signals are averaged , which reduces random interference.

AEP subgroups

AEP can be measured from the start of the stimulus with different measurement conditions for a duration of 1000 ms. They are divided into four intervals:

  1. 0-10 ms early acoustic evoked potentials (FAEP)
  2. 10–100 ms mean acoustic evoked potentials (MAEP)
  3. 100-300 ms late acoustic evoked potentials (SAEP)
  4. > 300 ms very late acoustic evoked potentials (SSAEP)

In each interval a typical sequence of maxima and minima is described, called "waves". The time between the stimulus and the typical waves is called latency , the signal swing between wave maximum and minimum is called amplitude . Out of clinical habit, the FAEPs are applied inverted to the other AEP components (MAEP, SAEP, SSAEP) (positive signal components point downwards in the FAEP).

literature

James W. Hall: New Handbook of Auditory Evoked Potentials . Pearson, Boston, Mass. 2006, ISBN 978-0-205-36104-5 .

Individual evidence

  1. ↑ Picton TW, Hillyard SA, Krausz HI, Galambos R: Human auditory evoked potentials. I. Evaluation of components Electroenceph Clin Neurophysiol 36: 179-190 (1974)