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.