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Fading into the background

A new study published here – Distinct Patterns of Neural Habituation and Generalization in Children and Adolescents With Autism With Low and High Sensory Overresponsivity – on pubmed.com explores how the brain can fade repetitive or familiar sounds in order to allow concentration in neurotypical persons and compares the workings of the same function in neurodiverse individuals.

For most of us, sensory stimuli such as noises or unusual textures trigger activity in the part of our brain which processes sensory information. The more we are exposed to this stimuli, the more our brain is able to recognise it as familiar and tamp or manage our response to it. This process, called habituation. It helps us tune out background noise/sensations so that we can pay attention and process new information. Let’s take a fan as an example – you hear it when it’s turned on at the start of the day, you feel it every time it turns towards you, but you don’t keep hearing that buzz or noticing the gust every second throughout the day, unless you choose to.

The article’s objective is to explore sensory overresponsivity (SOR), which is an atypical negative reaction to sensory stimuli prevalent in autism spectrum disorder. The study monitored responses in three stages of sensory processing:  initial response, habituation (i.e., change in response over time), and generalisation of response to new but familiar stimuli.

The new study, by lead investigator Shulamite Green  (assistant clinical professor of psychiatry and biobehavioral sciences at the University of California, Los Angeles), found that some autistic children don’t show signs of habituation. This means that their brain does not fade out the sound of a fan, the gust of wind, a stray hair that tickles their neck but their brain keeps trying to understand the stimuli over and over again – which is overwhelming and exhausting.

You can read the very interesting findings at length through the link above. The summary is:

  • The team studied brain responses to sensory stimuli in 42 children with autism and 27 non-autistic children, ages 8 to 18 years, who have average or above-average intelligence.
  • The autistic children into two groups: highly responsive to touch and sound and those less responsive. 
  • Each child’s brain was scanned while it experienced a series of stimuli, each lasting 15 seconds: white noise, a scratchy sponge rubbed along the left arm, and then both at once. The sequence looped six times.
  • The team monitored the regions of the brain which process sound and touch, and the amygdala, which filter sensory information.
  • During the first two rounds of repetition, all children showed increased brain activity. The group with the less responsive children had a noticeable brain activity drop during the third and fourth rounds and remained low for the fifth and sixth.
  • The brain activity of autistic children with high sensory reactivity veered towards high for all six repetition rounds.

The team also exposed the children to one more round of stimuli using similar sensations but with a slight difference in texture and frequency. The brain activity for the group with the low sensory reactivity indicated that they recognised the stimuli as new but also that they were similar enough to tune them out. Whereas, the other group had high brain activity which may indicate that their brains were processing the stimuli as completely separate and new. It was also interesting to read that some children with autism showed no brain response to the new stimuli at all. This may mean that they could not tell that the stimuli were new, or that their brains had faded the response to the original stimuli so much that they couldn’t activate in response to the new information.

Next time you see a child covering their ears, a parent frantically trying to to put their sock back on, a crying toddler in a busy train/bus/airplane – remember that what you see is never the whole story. Our bodies and minds are vast and beautiful and different. Instead of getting annoyed let your brain fade it out so you can focus on something else – because you have that ability and they may not. Your brain’s natural reaction will be to habituate not to stare or glare or offer unnecessary parenting advice – so pop your headphones in, look out the window or engage in another conversation instead of focusing on the distraction – because you have a choice, people with autism may not.

If you would like a taster of what sensory overload can be like Autism Speaks has 5 video simulations that help you experience sensory overload.

Don’t let kindness, understanding and love fade into the background. See it, appreciate it, teach it and use your capabilities for good.

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