Search

Objectives Direct challenge of cortical serotonergic (5-hydroxytryptamine, 5-HT) availability by tryptophan depletion test (TDT) was used to assess the hypothesized inverse relationship between central 5-HT function and loudness dependence of auditory evoked potentials (LDAEPs). Gender must be taken into particular account here, since there are gender differences in 5-HT brain synthesis, with women reacting more strongly to TDT. Methods In a double-blind, controlled cross-over study, 16 healthy females were ingested two highly concentrated amino acid mixtures with (+TRP) or without TRP (−TRP). While monitoring TRP levels and mood states, the AEP of different loudness stimuli were recorded, followed by dipole source analysis. Results Under the −TRP condition, free plasma TRP levels decreased by 81.10% (±5.14). Most of the loudness change rates of the relevant N1/P2 tangential dipole activities were significantly increased under −TRP, but calculated LDAEP did not differ significantly between treatments. LDAEP and states of mood were not correlated. Conclusions Despite strong TRP depletion, the results did not reach sufficient evidence that LDAEP is a valid biological marker of central 5-HT activity in females when using TDT. This agrees with the literature and supports the view that LDAEP indicates predominantly biological vulnerability in predisposed individuals. Copyright © 2007 John Wiley & Sons, Ltd.

Human cortical somatosensory evoked potentials (SEPs), which are presumably generated in afferent thalamocortical and early cortical fibers, reveal a burst of superimposed early (N20) high-frequency oscillations (HFOs), around 600 Hz. There is increasing evidence of an imbalance of thalamocortical systems in schizophrenic patients. In order to assess correlations between somatosensory evoked oscillations and symptoms of schizophrenia, we investigated median nerve SEPs in 20 inpatients and their age-matched and gender-matched healthy controls using a multichannel EEG. Dipole source analysis and wavelet transformation were performed before and after application of a 450-Hz high-pass filter. In schizophrenics, the maximum HFOs occurred with a significantly prolonged latency. There was also a higher amplitude (energy) in the low-frequency range of the N20 component compared with the controls. Importantly, amplitudes (energy) of HFOs were inversely correlated with symptoms of formal thought disorder and delusions. Alterations of the thalamocortical somatosensory signal processing in schizophrenia with absence of an early HFO – assumed to be of inhibitory nature – could indicate a dysfunctional thalamic inhibition with increased amplitudes of N20, paralleled by enhanced positive schizophrenic symptoms.