1. ¹Department of Psychiatry, Ludwig-Maximilians-University, Munich, Germany
2. ²Department of Nuclear Medicine, Ludwig-Maximilians-University, Munich, Germany
3. ³Psychosomatic Hospital Windach, Germany

Correspondence: Dr O Pogarell, Department of Psychiatry, Section of Clinical Neurophysiology, Ludwig-Maximilians-University of Munich, Nussbaumstr. 7, D-80336 Munich, Germany. Tel: +49 89 5160 3409; Fax: +49 89 5160 5542; E-mail: oliver.pogarell@med.uni-muenchen.de

Received 22 March 2004; Revised 6 July 2004; Accepted 6 July 2004; Published online 4 August 2004.

Abstract

Brain monoaminergic function is involved in the pathophysiology of psychiatric disorders. The loudness dependence (LD) of the N1/P2 component of auditory evoked potentials has been proposed as a noninvasive indicator of central serotonergic function, whereas single photon emission computed tomography (SPECT) and [¹²³I]-CIT can be used to visualize both serotonin (SERT) and dopamine transporters (DAT). The aim of the study was to correlate LD and SPECT measures in patients with obsessive-compulsive disorder, a condition with evidence for a serotonergic dysfunction. A total of 10 subjects received both neurophysiological and imaging investigations. Evoked potentials were recorded following the application of acoustic stimuli with increasing intensities. The LD of the relevant subcomponents (tangential dipoles) was investigated using dipole source analysis. SPECT was performed 20–24 h after injection of a mean 140 MBq [¹²³I]-CIT. As a measure of brain SERT and DAT availabilities, a ratio of specific to nonspecific [¹²³I]-CIT binding for the midbrainpons region (SERT) and the striatum (DAT) was used. The LD of the right tangential dipole correlated significantly with both SERT and DAT availabilities (Pearson's correlations: =0.69, p<0.05, and =0.80, p<0.01, respectively). The correlations remained significant after controlling for the effects of age, gender, and severity of clinical symptoms. Associations between LD and both SERT and DAT availabilities further validate the use of neurophysiological approaches as noninvasive indirect measures of neurochemical brain function and point at a hypothesized interconnection of central monoaminergic systems.