Intensity dependence of auditory evoked potentials (AEPs) as biological marker for cerebral serotonin levels: effects of tryptophan depletion in healthy subjects

Psychopharmacology (Berl). 1999 Sep 1;146(1):101-7. doi: 10.1007/s002130051094.


Rationale: The intensity dependence of the auditory evoked potentials (AEP) has been suggested to be a specific biological marker of central serotonergic activity.

Objective: While previous studies used circumstantial evidence to support this hypothesis, we manipulated (decreased) cerebral levels of serotonin directly by using tryptophan depletion.

Methods: Twelve healthy young subjects were investigated using placebo and two different amino acid mixtures in a double blind cross over design on three different occasions. AEPs recorded during tryptophan depletion were analyzed by dipole analysis and regional sources using methods published in the literature.

Results: For none of the mixtures a significant effect of tryptophan depletion was found. There was a trend towards reduced intensity dependency after tryptophan depletion, especially in the right hemisphere. This reduction correlated with the amount of reduced tryptophan in plasma.

Conclusions: The results indicate, in contrast to earlier indirect studies, that the intensity dependence of AEPs is not a specific marker of central serotonergic activity.

Publication types

  • Clinical Trial

MeSH terms

  • Adult
  • Biomarkers
  • Brain Chemistry*
  • Cross-Over Studies
  • Double-Blind Method
  • Evoked Potentials, Auditory*
  • Female
  • Humans
  • Male
  • Serotonin / analysis*
  • Tryptophan / analysis*
  • Tryptophan / blood


  • Biomarkers
  • Serotonin
  • Tryptophan