Men with autism spectrum disorder (ASD) respond differently to social chemical signals that are not consciously perceived, sometimes displaying the opposite responses to those of individuals without ASD, reports a study published online this week in Nature Neuroscience. This finding could explain in part why individuals with ASD misread emotions.
Mammals typically rely on their sense of smell to read emotions and communicate socially through the perception of chemical signals (chemosignals), and there is growing evidence for meaningful social chemosignaling in humans as well. Human chemosignals have been shown to convey information such as age, aggression, happiness, and fear, and they can act subliminally to influence brain activity and general psychological and emotional states.
Noam Sobel and colleagues find that unconscious exposure to the ‘smell of fear’ - sweat produced by skydivers, who were stressed (as measured by cortisol levels) - increased activity of the autonomic nervous system (the part of the nervous system responsible for unconscious bodily functions, like breathing and heartbeat) in neurotypical individuals but not in people with ASD. The authors also find that a mannequin emitting this fear chemosignal was less trusted by neurotypical individuals than a mannequin emitting the sweat from people walking calmly, but participants with ASD reported trusting the mannequin emitting the ‘smell of fear’ more. Moreover, unconscious exposure to two different synthetic chemosignals also had opposite effects in neurotypical participants and individuals with ASD.
he authors find that both groups had an intact sense of smell, because they responded similarly when asked to differentiate and rate body odours and only responded differently to chemosignals they did not consciously detect. The authors speculate that an altered response to chemosignals is more likely to have profound effects than not being able to respond to them at all, as altered responses may lead to misreading of emotional signals.