Comparison between the analysis of the loudness dependency of the auditory N1/P2 component with LORETA and dipole source analysis in the prediction of treatment response to the selective serotonin reuptake inhibitor citalopram in major depression.

ABSTRACT

OBJECTIVES: The loudness dependency of the auditory evoked potentials (LDAEP) is used as an indicator of the central serotonergic system and predicts clinical response to serotonin agonists. So far, LDAEP has been typically investigated with dipole source analysis, because with this method the primary and secondary auditory cortex (with a high versus low serotonergic innervation) can be separated at least in parts. METHODS: We have developed a new analysis procedure that uses an MRI probabilistic map of the primary auditory cortex in Talairach space and analyzed the current density in this region of interest with low resolution electromagnetic tomography (LORETA). LORETA is a tomographic localization method that calculates the current density distribution in Talairach space. RESULTS: In a group of patients with major depression (n=15), this new method can predict the response to an selective serotonin reuptake inhibitor (citalopram) at least to the same degree than the traditional dipole source analysis method (P=0.019 vs. P=0.028). The correlation of the improvement in the Hamilton Scale is significant with the LORETA-LDAEP-values (0.56; P=0.031) but not with the dipole source analysis LDAEP-values (0.43; P=0.11). CONCLUSIONS: The new tomographic LDAEP analysis is a promising tool in the analysis of the central serotonergic system.