Alarm substances are airborne chemical signals, released by an individual into the environment, which communicate emotional stress between conspecifics. Here we tested whether humans, like other mammals, are able to detect emotional stress in others by chemosensory cues. Sweat samples collected from individuals undergoing an acute emotional stressor, with exercise as a control, were pooled and presented to a separate group of participants (blind to condition) during four experiments. In an fMRI experiment and its replication, we showed that scanned participants showed amygdala activation in response to samples obtained from donors undergoing an emotional, but not physical, stressor. An odor-discrimination experiment suggested the effect was primarily due to emotional, and not odor, differences between the two stimuli. A fourth experiment investigated behavioral effects, demonstrating that stress samples sharpened emotion-perception of ambiguous facial stimuli. Together, our findings suggest human chemosensory signaling of emotional stress, with neurobiological and behavioral effects.

Anticipation is a central component of anxiety and the anterior insula appears to be an important neural substrate in which this process is mediated. The anterior insula is also thought to underlie the interoceptive representation of one's affective state. However, the degree to which individual differences in anticipation-related insula reactivity are associated with variability in the subjective experience of anxious anticipation is untested. To assess this possibility, functional magnetic resonance images were acquired while participants completed an auditory anticipation task with trial-by-trial self-report ratings of anxious anticipation. We hypothesized that the anterior insula would be positively associated with an individual's subjective experience of anticipatory anxiety. The results provide evidence for an amygdalo-insular system involved in anxious auditory anticipation. Reactivity in the right anterior insula was predictive of individuals' subjective experience of anxious anticipation for both aversive and neutral stimuli, whereas the amygdala was predictive of anticipatory anxiety for aversive stimuli. In addition, anxious anticipatory activation in the left insula and left amygdala covaried with participants' level of trait anxiety, particularly when the anticipated event was proximal.

Near infrared spectroscopy (NIRS) is a non-invasive optical imaging technique that can be used to measure cortical hemodynamic responses to specific stimuli or tasks. While analyses of NIRS data are normally adapted from established fMRI techniques, there are nevertheless substantial differences between the two modalities. Here, we investigate the impact of NIRS-specific noise; e.g., systemic (physiological), motion-related artifacts, and serial autocorrelations, upon the validity of statistical inference within the framework of the general linear model. We present a comprehensive framework for noise reduction and statistical inference, which is custom-tailored to the noise characteristics of NIRS. These methods have been implemented in a public domain Matlab toolbox, the NIRS Analysis Package (NAP). Finally, we validate NAP using both simulated and actual data, showing marked improvement in the detection power and reliability of NIRS.