Autism and the sense of smell
Our sense of smell helps us detect various odours and fragrances and helps us identify the source of those smells. This sense is also closely linked to parts of the brain that process emotion and memory.
Although it is not our primary sense, it can subliminally react to certain odours as it does in mammals such as the “smell of fear”. Although this is not a conscious odour, when we smell fear, we do it without thinking. This is a form of social communication.
Autism is typically characterised by impaired social communication due to misreading of emotional cues. We often attribute that to visual difficultly in reading facial expressions.
The autism group had the opposite effect to the control group – the calm odour induced less trust in the mannequin while the fear-induced sweat made them display more trust.
It is unclear why people with autism misread emotions but a new research from the Weizmann Institute of Science suggests that the sense of smell plays a key role in autism and explains how people with autism read emotions.
For this study a series of experiments was devised with a group of participants who included people on the high-functioning end of autism spectrum.
To begin the experiments, the researchers tested the ability of both the control volunteers and volunteers with autism to be able to identify smells that can be consciously detected such as the smell of human sweat.
There was not significant difference in both the groups indicating that the sense of smell in people with autism was not any different from control volunteers at this stage.
The two groups were then exposed to the “smell of fear” and a control odour. The “smell of fear” was the sweat from people taking skydiving classes while the control odour was the sweat from the same people, only this time it was collected while they were just exercising – without feeling any fear.
Both the groups reported no dissimilarities between the two smells, but their bodies reacted differently.
In the control group, the “smell of fear” induced increased fear response but sweat from exercising did not.
The opposite effect was seen in people with autism. The fear-induced sweat reduced their fear response but the calm sweat increased measurable levels of anxiety.
In the next experiment, talking robotic mannequins were used. These mannequins emitted a particular odour while talking. The mannequins gave the volunteers different tasks to complete. With these mannequins the researchers had complete control over all the social cues. The tasks were designed to measure the level of trust a volunteer had in the mannequin.
Here too, the results were similar. The autism group had the opposite effect to the control group – the calm odour induced less trust in the mannequin while the fear-induced sweat made them display more trust.
In other experiments volunteers were exposed to sudden loud noises during the session while also being exposed to calming component of body-odour called hexadecanal.
Another automatic fear response – blinking – was recorded using electrodes above the muscles of the eye.
The blink response was weaker in the control group when exposed to hexadecanal than the autism group whose blink response was stronger to hexadecanal.
This study shows that the autism volunteers did not display an inability to read olfactory social cues but rather they misread them.
This, points to a deeper connection between our sense of smell and development at an early age with recent research pointing to the role nasal receptors play in development.
Perhaps the sensing of subtle chemical signals goes askew in people with autism during the crucial stages of early development – explaining why people with autism react differently to olfactory cues.
Source: Nature Neuroscience
