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Altered Responses to Social Chemosignals in Autism Spectrum Disorder
Social chemosignals are volatiles secreted by one individual to affect the behavioral, physiological, brain activity and hormonal state of other individuals. A Growing body of evidence implies that social chemosignals likely play a major role in human social interaction, mostly without conscious awareness.
Objectives: Because Autism spectrum disorder (ASD) is characterized by impaired social communication, often attributed to misreading of emotional cues, we hypothesized that misreading of emotional cues in ASD partially reflects altered social chemosignaling.
Methods:
In a series of experiments we investigated this hypothesis by comparing the physiological and behavioral responses of typically developed (TD) adults and cognitively able adults with ASD to the subliminal presentation of social chemosignals. In the first two experiments, we tested the effects of smell of fear (actual body-odor collected from first-time tandem skydivers). We tested the physiological responses to the smell of fear in both TD (n =20) and ASD (n=20) participants, and in a second experiment we tested how TD (n =20) and ASD (n=20) participants respond behaviorally to the smell of fear. Then, we tested the impact of two different isolated putative social chemosignals. The first is a commonly studied putative social chemosignal, 4,16-androstadien-3-one (AND). we measured the impact of AND on physiological measures using a widely applied assay for human chemosignaling (TD, n =23, ASD, n = 17). The other chemosignal tested is a novel putative compound, hexadecanal (HEX), a molecule that promotes social buffering in rodents. Given that HEX is also present in human skin, we measured the impact of HEX on the acoustic startle response, a brainstem aversive reflex that occurs after a startling event such as a loud noise (TD, n =17, ASD, n = 17).
Results:
The undetected smell of fear increased physiological arousal in TD yet did not affect arousal in ASD (F1,34 = 12.8, p = 0.001). In addition, the undetected smell of fear reduced explicit and implicit measures of trust in TD, but acted opposite in ASD (F1,37 = 10.1, p < 0.003). The putative chemosignal AND drove increased arousal in TD yet decreased arousal in ASD (F1,37 = 8.0, p = 0.007). Finally, the putative chemosignal HEX significantly reduced startle in TD but not in ASD (F1,30 = 7.7, p < 0.01).
Conclusions: Experiments with subliminal presentation of a natural stimulus (smell of fear) and two different synthetic putative social chemosignals (AND and HEX) converged to imply altered autonomic and behavioral responses to social chemosignals in ASD. I speculate that altered response to chemosignals may be involved in part of the symptoms of ASD. This speculation suggests novel paths of research, diagnosis, and treatment.