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Men with autism may misread social cues in body odors

by  /  21 December 2017
T-shirt test: People with autism can distinguish among different people’s T-shirts by smell but do not react to these odors in the typical way.

Men with autism respond differently to human odors — and the social signals that they contain — than do their neurotypical peers, according to a new study1.

The results suggest that men with autism misread social signals present in human odors — causing them to misinterpret others’ emotions.

Human sweat contains chemicals believed to convey social and emotional information. For instance, when women smell sweat collected from men watching scary movies, they are more likely to describe faces with ambiguous expressions as fearful2.

In the new study, researchers exposed men to sweat collected from people who were skydiving. Unlike controls, men with autism do not show increased skin conductance, a measure of physiological arousal, to this ‘fear sweat.’ They are also more likely than controls to trust a mannequin that emits this scent.

“I think this could be a meaningful aspect of impaired social interaction,” says lead investigator Noam Sobel, professor of neurobiology at the Weizmann Institute of Science in Rehovot, Israel. “Humans constantly engage in social chemo-signaling; we do this all the time, and it shapes our interactions,” he says. “And somehow these mechanisms work differently in autism.”

Several studies have examined olfaction in people with autism. Researchers have found, for example, that children with autism inhale odors differently than their typical peers do, and some children with the condition may be particularly sensitive to smells.

But there has been little work on how people with autism process the social information contained in body odors.

The new paper is provocative because it suggests that the communication problems that accompany autism may extend to chemical forms, says Johannes Frasnelli, professor of anatomy at the University of Quebec at Trois-Rivières in Canada, who was not involved in the research.

However, little is known about how people communicate through odors. “I think what this paper does is it generates hypotheses; it looks at the problem from a very interesting angle,” Frasnelli says. The topic “definitely deserves more research,” he says.

The smell of fear:

Sobel and his colleagues began by assessing the basic olfactory skills of 16 men with autism and 18 controls. They asked the participants to sniff three samples of body odor, two of which were from the same person, and pick out the one that did not belong.

The participants with autism performed just as well on this task as their peers did, suggesting that they are not impaired in their ability to detect and distinguish among odors.

The researchers then asked 15 men with autism and 15 controls to rate sweat samples collected from skydivers. Both groups reported that the smell of this perspiration was more intense, less pleasant and connoted higher levels of fear than sweat collected from men who had been walking calmly.

Despite the similarity of these ratings, however, the fear sweat prompted markedly different bodily reactions in the two groups of men. The controls showed a significant increase in skin conductance while smelling the fear sweat, but not the walking sweat. Men with autism, however, did not show an elevation in arousal.

To assess how the chemical signals in fear sweat might influence the men’s behavior, Sobel’s team built two robotic mannequins, one that gave off fear sweat and another that emitted a control odor (sports sweat). The mannequins were also programmed to help the participants in a cognitive test, providing them with spoken hints to help them quickly locate and click on a target on a computer screen.

Both mannequins gave advice that was correct 70 percent of the time. Still, the controls put more trust in the hints provided by the mannequin that emitted sports sweat than in those provided by the one that gave off the fear sweat; the opposite was true of the men with autism.

The results were published in Nature Neuroscience on 27 November.

Mixed signals:

The results suggest that although men with autism can detect the chemical signals in fear sweat, they interpret and react to these signals differently than controls do.

The study “really shed light on the fact that it’s not the explicit processing of odors that are impaired in autism, but the implicit processing of the social cues in odors,” says Bruno Wicker, a neuroscience researcher at the French National Center for Scientific Research and Aix-Marseille University in Marseille, France, who was not involved in the study.

This distorted signal processing may be particularly problematic because it occurs largely without conscious awareness.

“You can’t do anything to mitigate this wrong message,” Sobel says. “You’re unaware of getting a message at all, let alone that it’s wrong. So this obviously would pose a major obstacle and barrier to social interaction.”

The underlying reason for these differences is unclear, but it may be that olfactory receptors in people with autism go awry. Because these receptors are located throughout the brain, the problem could derail multiple aspects of brain development, the researchers say.

  1. Endevelt-Shapira Y. et al. Nat. Neurosci. Epub ahead of print (2017) PubMed
  2. Zhou M. and D. Chen Psychol. Sci. 20, 177-183 (2009) PubMed
  • C Stargazer

    Well that was an amusing read. It’s yet another layer of verification that we do not communicate on base animal levels and depend on literal meanings, logic and direct communication. We lack many of the genetic throwbacks to the animal kingdom.

    If anything, I would consider it a deficit for someone to depend on odors and body language to communicate.

  • Sherine Gilmour

    I think it would be interesting for the researchers to do a follow-up comparing the reactions of (a) a group of people with ASD to (b) a group of NT people in an already developed fear state or anxiety state. Then compare the results involving the mannequin and sweat.

  • Kal

    Why is the autistic people’s response considered inaccurate here? Would a person who emits the smell of fear be less likely to provide accurate advice or to be trustworthy? Without the answer to that question, we don’t know whose response is correct. Perhaps the non-autistic people were wrong to mistrust a fearful advice giver.

    • Zoran Bekric

      I have to echo this question. The report just assumes that distrusting people who smell of fear because they have been skydiving — or, more simply, distrusting skydivers — is correct. It makes no attempt to establish that those who smell of fear are less trustworthy, especially since in the experiment described, the mannequins giving hints, they weren’t.

      The results of this research could just as legitimately and accurately be headlined:
      “Men with autism display less unconscious bias based on body odors”.

  • Sharwan Kumar

    I am surprised that spectrum is publishing this news item so late. I have already read this news item elsewhere already, last month. Please publish the news items concerning autism research as soon as they are published or presented.
    What has not been mentioned is how did the fear sweat differed from the non- fear sweat. What chemicals are there which could be associated with emotion connected with fear? Are those chemicals well known to represent fear or are they the ones that the authors think to be those that cause fear, fear due to height only or all types of fear? What are those chemicals after all? To be contd…

  • Sharwan Kumar

    Can not comment further unless original article is provided to me. In order to have access to the article published in the journal, one has to pay for it.
    The authors should always publish such articles in journals that are freely available to the public. In fact, I am of the opinion that authors should make their personal websites and upload their articles therein. The university system of promotions is stupid that asks teachers to publish papers in journals that are peer reviewed. Promotions should be based on teaching results and not on research results.


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