1. ¹Department of Psychology, Dresden University of Technology, Dresden, Germany
2. ²Department of Neuroscience, Section of Pharmacology, Uppsala University, Uppsala, Sweden
3. ³Department of Psychiatry and Psychotherapy, University of Würzburg, Würzburg, Germany

Correspondence: T Hensch, Department of Psychology, Dresden University of Technology, Mommsenstr. 13, Dresden 01062, Germany. Tel: +49 351 463 36999, Fax: +49 351 463 36993, E-mail: Tilman.Hensch@tu-dresden.de

Received 11 July 2005; Revised 4 November 2005; Accepted 28 November 2005; Published online 18 January 2006.

Abstract

Intensity dependence of auditory-evoked potentials (IAEP) has been suggested as an indicator of central serotonergic neurotransmission. Two recent studies investigated a possible association of IAEP with a functional polymorphism in the transcriptional control region of the serotonin transporter gene (5-HTTLPR) that has a short (s) and a long (l) variant. Although both studies found an association between 5-HTTLPR and IAEP, Gallinat et al found l/l individuals to exhibit lower IAEP, whereas Strobel et al observed stronger IAEP in l/l individuals. These conflicting results require further evaluation and more attention needs to be paid to variables that are known to be confounded with the effects of IAEP and 5-HTTLPR. Using a paradigm comparable to Strobel et al, the present study analyzes the effect of 5-HTTLPR on IAEP in a healthy male student sample (N=91; age=23 years, SD=1.9) that was homogenous for most significant confounding variables. A stronger IAEP was shown in l/l individuals, irrespective of the method of IAEP parametrization. This also held at retest after 3 weeks in a subsample (N=18). Given the successful replication of Strobel et al, several possible reasons for conflicting results with regard to Gallinat et al are discussed. It is argued that the most significant difference between Gallinat et al on the one hand, and Strobel et al and this study on the other, is that different intensity ranges are used which impact IAEP. Therefore, this study encourages further analysis of dose dependence of results.