Autism and the Smell of Fear.

• Author: Sobel, Noam

Autism typically involves the inability to read social cues. We most often associate this with visual difficulty in interpreting facial expression, but research at the Weizmann Institute of Science suggests that the sense of smell also may play a central role in autism. As we reported in Nature Neuroscience, it can be shown that people on the autism spectrum have different--and even opposite--reactions to odors produced by the human body.

These odors are ones that we are unaware of smelling, but which are, nonetheless, a part of the nonverbal communication that takes place between people, and which have been shown to affect our moods and behavior. The findings may provide a unique window on autism, including, possibly, on the underlying developmental malfunctions in the disorder.

Researchers in the lab investigate, among other things, the smells that announce such emotions as happiness, fear, or aggression to others. Although this sense is not as dominant in humans as it is in many other mammals, we still subliminally read and react to certain odors. For instance, "smelling fear," even if we cannot consciously detect its odor, is something we may do without thinking. Since this is a form of social communication, we thought it might be disrupted in a social disorder like autism.

To conduct our experiments, lab members devised a series of experiments with a group of participants on the high-functioning end of the autism spectrum who volunteered for the study. To begin with, we tested the ability of both autistic and control volunteers to identify smells that can be detected consciously, including human smells like sweat. There was no significant difference between the groups at this stage, meaning the sense of smell in the autistic participants was not significantly different from that of controls.

Two groups then were exposed either to the "smell of fear" or to a control odor. The smell of fear was sweat collected from people taking skydiving classes, and control odor was sweat from the same people, only this time it had been collected when they were just exercising, without feeling fear.

This is where differences emerged. Although neither group reported detecting dissimilarities between the two smells, their bodies reacted to each in a different way. In the control group, smelling the fear-induced sweat produced measurable increases in the fear response (for example, in skin conductivity), while the everyday sweat did not. In the autistic...