Influence of Neurexan® on brain activity in responses to deviant stimuli during an auditory oddball task

Abstract

Background: Neurexan®, a medicinal product sold over the counter (OTC), contains four ingredients; Passiflora incarnata (passionflower), Avena sativa (oats), Coffea arabica (coffee) and Zincum isovalerianicum (zinc valerianate). Neurexan® has been investigated in patients with symptoms related to acute stress, nervousness/restlessness, and insomnia. The previous research suggested an attenuated neuroendocrine stress response in healthy volunteers induced by Neurexan® (Doering et al. 2016). This study further explores the effects of Neurexan® on cognitive performance and attention that can be assessed by the oddball paradigm. It is generally recognized that stress is associated with cognitive impairments. Expecting that Neurexan® reduces the stress level, we hypothesized that the subjects in the placebo group would be more susceptible to distraction compared to treatment group. Methods: In a randomized, placebo-controlled, double-blind, two-period crossover trial, brain responses to the unattended auditory oddball task of 39 healthy, moderately stressed males were measured with 64-channel electroencephalogram (EEG) after intake of a single dose of Neurexan® or placebo. The paradigm consisted of 80 standard tones and two types of deviant tones (10 frequency deviant; 10 duration deviant), presented in a pseudo-randomized order. The standard tone was composed of eight equally loud sinusoidal tones (fundamental frequency 330 Hz and seven harmonic partials) and had the duration of 100 ms. The deviants were either 40 ms shorter (duration deviant) or 1.25 semitones higher (frequency deviant). Results: Significant effect of Neurexan® on the latency of mismatch negativity (MMN) (decreased latency under treatment) was observed with repeated-measures ANOVA. The main effect of the treatment (F(1,37)=4.297, p=0.045, η2= 0.104) and significant treatment x deviant-type interaction (F(1,37)=8.828, p=0.005, η2=0.193) were found. Further Wilcoxon-test for paired samples showed that this reductione of latency was present for the frequency deviant stimuli (z(37)=-2.85, p=0.004). Conclusion: Significant reduction of MMN latency in the Neurexan treatment group suggests that Neurexan® induces subtle primary processing changes in term of reaction time