Differential Processing of Body Odors and Common Odors in ASD: Sensory-Motor Vs. Emotional Analysis

Background: There is emerging evidence from ASD samples for associations between olfactory processing and social engagement as well as for manifestations of anxiety. There is likewise evidence for links between neuroanatomical networks implicated in ASD and networks known to support typical olfactory processing. Studies of social and nonsocial olfaction may shed light on these associations. Body odors provide a wealth of social information and their brain processing is distinguished from that of common odors in typical individuals. However, there are no reported neuroimaging studies of either social or nonsocial olfactory processing in ASD.

Objectives: The goal of the present study was to compare the neural bases of social body odors versus common, nonsocial odors in adults with ASD and neurotypical controls. Specifically, we are interested in dissociating familiar and unfamiliar masked body odors to evaluate detection for signals of implicit threat.

Methods: Preliminary results are based on 45 healthy adult volunteers including ASD (n=22) and neurotypical comparison (NT; n=23) participants. During fMRI scanning, participants were asked to indicate the intensity and pleasantness of various odors including clean air (baseline), a neutral common odor (cedarwood oil), and two body odors masked with the neutral odor (i.e., participants could consciously only smell the cedarwood). One odor was from a familiar individual (family or roommate) and the other was the odor of a stranger. We conducted two-way ANOVA with diagnosis as between-subject factor and odor condition as a within-subject factor. These preliminary results are uncorrected, p<0.008.

Results: Results indicate that both groups processed body odors in distinct networks from the nonsocial common odor. However, the ASD group activated more sensory areas than controls for both body odor conditions. In contrast, the control group activated insula and amygdala more than the ASD group for familiar but not unfamiliar body odors.

Conclusions: These results suggest that individuals with ASD are able to distinguish social from common odors, but do so on based on analyzing sensorimotor properties of the stimuli rather than relying on the relevant social information embedded in body odors. To our knowledge, this is the first neuroimaging study to reveal the neural basis for atypical odor-mediated social communicative behaviors in ASD. Difficulties with discrimination of implicit emotional stimuli may likewise contribute to ongoing states of uncertainty that underlie anxiety in many people diagnosed with ASD.