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Abstract:
Introduction:
Human sweat contains chemosignals that have been shown to increase state anxiety in women (Albrecht et al. 2011), and increase reaction times to anxiety-related words (Mutic et al. 2016). Human sweat contains a mixture of different compounds including androgens like androstadienone (4,16-androstadien-3-one, AND). AND has recently been discussed to influence attention in social contexts showing that under AND-exposure heterosexual women spent more time looking at female faces (Parma et al. 2012) and rated male faces more attractive (Ferdenzi et al. 2016).
Concerning neural activation, studies on AND-action have mostly been limited to passive inhalation of the compound (Berglund et al. 2006, Burke et al. 2012) which led to increased hypothalamic activation. Given its effects on attention we sought to investigate the neural underpinnings of AND-action in a task tapping emotional interference (Stroop task).
Based on partial evidence from previous studies (Hummer and McClintock 2009, Frey et al. 2012) we first hypothesized that under AND compared to a placebo odor both men and women will pay more attention to task-relevant emotional faces but less attention to non-relevant emotional words resulting in a weaker emotional conflict in the Stroop task. Concomitantly this should also be reflected in reduced activation in brain regions important for monitoring and resolving response conflicts, e.g. the inferior frontal gyrus and the inferior parietal lobe (Chechko et al. 2012). Furthermore, independent of stimulus-congruency, we expected AND to elicit stronger activation in regions implicated in emotional processing, e.g. the amygdala, the right orbito-frontal cortex and the right lateral prefrontal cortex (Hummer et al. 2016).
Methods:
We recruited 15 healthy men and 15 women taking oral contraceptives (mean age=23.55 years, SD=2.91 years) and tested them repeatedly once under AND- and once under placebo-exposure. Functional MRI-scanning was performed on a 3T Trio MR scanner (Siemens Medical Systems, Erlangen, Germany) at the Medical Faculty, University of Tübingen, Germany.
Participants completed an emotional Stroop task (Figure 1) to assess interference control (Chechko et al. 2012). The emotional Stroop task creates a response conflict due to the incompatibility of an emotional target (word) and emotional distractor (face) stimulus.
Statistical analyses were accomplished using the software Statistical Parametric Mapping (SPM12, http://www.fil.ion.ucl.ac.uk/spm). A flexible factorial model was created including the factors sex (men, women), congruency (congruent, incongruent trials), emotion (happy, fearful, angry faces) and odor (androstadienone, placebo) to analyze the whole brain for significant activation. Furthermore, regions of interest were selected based on former studies including the amygdala, hypothalamus, right orbitofrontal and right lateral prefrontal cortex.
Supporting Image: Figure1.jpg.
Results:
Although we detected strong behavioral interference and enhanced neural activation in areas implicated in response conflict (inferior frontal gyrus, inferior parietal lobe) neither men nor women showed reduced interference on behavior or neural activation level during AND-exposure Furthermore, AND did not modulate neural activation in an emotion- or sex-specific way. However, region-of-interest analyses detected enhanced activation of the left amygdala during AND compared to PLAC (Figure 2) but failed to detect AND-effects in other areas involved in emotional processing, e.g. the right orbitofrontal and lateral prefrontal cortex.
Furthermore, a general sex effect emerged showing enhanced neural activation for men compared to women in the inferior occipital and fusiform gyrus implicated in facial and emotional processing.
Conclusions:
We did not find changes in the neural signature of emotional intereference under the putative human chemosignal AND. However, we show initial evidence that AND modulates amygdala activation in both men and women.
