Impaired somatosensory processing is often found in neurodevelopmental conditions. Researchers are paying closer attention to the meaning of deficits in this sensory system and its possible impact on autistic individuals.
We’re all a little touchy about, well, touch at the moment. The pandemic’s social distancing made human touch a rare commodity. It left many craving a tight hug from a friend while, for others, touch will continue to symbolize the spreading of a much feared virus. Perhaps our new reaction to touch will make us a little more sensitive to the feelings of those who have never experienced touch in a typical way.
Autism is inextricably linked to sensory processing disorders. Leekam et al. (2007) found that over 90% of autistic children participating in a study had sensory abnormalities with sensory challenges in multiple sensory domains.
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Tactile (or perceptible to our sense of touch) defensiveness is a symptom that is often found in children with autism. Common signs include frequent mouthing of non-food objects, strong preference or aversion to food with specific textures, and these kids may prefer to touch others rather than being touched.
Over-reactivity to touch is a daily difficulty faced by individuals with a sensory processing disorder. It goes beyond hyper and hyposensitivity—in this article the focus will be on somatosensation, a sense involved in almost everything we do.
What is somatosensation?
The somatosensory system is part of the nervous system. It helps us to detect and perceive pain, temperature, head and body position, and, of course, touch (Jacobs, 2011). The somatosensory system is involved in many functions, and it plays a key role in fine and gross motor skill development. Somatosensation is often described as a mixed sensory category; the stimuli received comes not only from skin, but also from limbs and joints.
The somatosensory system includes receptors and neurons which convey information, such as body position and movement, to the brain. These receptors are found in skin, muscle, bone, and tendons.
The processing of information (pertaining to pain, touch, movement, and temperature) from these receptors are vital for survival, optimal environmental interaction, and it also serves important social and emotional functions.
In other words, our somatosensory system allows us to identify and react to tactile characteristics of our environment. Sensory atypicalities in this sphere would thus lead to abnormal reactions to sensory stimuli like temperature. Research tells us that sensory processing difficulties may have an influence on behavior, learning and everyday living. It is important, therefore, to examine how somatosensation could be affected in those on the spectrum.
Autism and somatosensory impairment
Sensory challenges in autism have not been studied with the same frequency and intensity reserved for aspects such as language impairment and communication deficits. A recent study (Dellapiazza, et al., 2020) set out from the preposition that, while abnormal sensory processing is common in autism spectrum disorders, the impact such atypical processing has on adaptive challenges and problem behaviors may not be well understood.
This study (Dellapiazza, et al., 2020) suggests that sensory processing atypicalities may explain a big part of behavioural problems for children with autism spectrum disorders (ASD). Can some of these behavioural problems be the direct result of deficits in the somatosensory system? Unfortunately there are only a few studies investigating the specific somatosensory challenges of children on the spectrum.
One such study (Büyüktaşkın et al., 2021) focused on somatosensory differences in autistic children. The study found that children with autism had a higher tactile discrimination threshold than typically developing children.
This study is important as it proposes a way in which we can actually measure sensory differences in autistic children. Research is finding evidence of what parents with autistic children have said for a long time—that sensory difficulties in ASD cause many of the behavioral challenges—but the problem faced by clinicians remains finding a way to measure sensory differences objectively and accurately.
The above mentioned study (Büyüktaşkın et al., 2021) suggests that measuring atypical sensory processing may aid deeper comprehension of clinical symptoms and neurobiological aspects of autism.
If studies pertaining to somatosensation (and its impact on autism) could pave the way to finding an objective measure of sensory processing challenges in autistic individuals, it already seems like a worthy endeavour. A further incentive to study the impact of deficits in the somatosensory system on autism, is the fact that it may help professionals, like occupational therapists, to streamline therapy to an optimal level for autistic children.
Addressing somatosensation challenges
Difficulties in measuring sensory differences in autistic individuals along with challenges in classifying sensory deficits seems to be a common theme in much of the applicable research. The precise mechanisms leading to under and over reaction of the nervous system in different circumstances and environments also seems complicated.
Parents often share how their autistic child may be hypersensitive to certain tactile stimulation like tags in his/her clothing. And yet when it comes to pain and temperature, the same child may be hyposensitive, seemingly unaware of painful sensations or extreme temperature.
The far reaching implications of atypical sensory response in autism was made apparent in a study by Cascio et al. (2012). Magnetic resonance imaging was used to investigate participants’ response to somatosensory stimulation. The results suggest that adults with ASD displayed a lesser response to neutral and pleasant stimuli, and an exaggerated response to unpleasant stimulatory input.
The authors suggest that this finding may validate the idea that autistic individuals experience less social reward from touch compared to neurotypical individuals. This may play a part in social withdrawal for individuals on the spectrum.
Symptoms of somatosensation deficits
For parents with a child on the spectrum, the research may confirm what they already know—sensory difficulties, including those of the somatosensory system, are at the root of not only behavioral issues, but such challenges may also cause emotional outburst or so-called meltdowns and lessen social motivation.
Parents who think their child may have difficulties processing somatosensory stimuli should monitor reactions of hyper and hyposensitivity across all senses. In particular, behavior like the following may need to be discussed with an occupational therapist:
- An indifference to pain and temperature
- Over-responsiveness or extreme sensitivity to texture evident in an abnormal reaction to tags in clothing. The child may insist on only wearing pajamas or clothing with a particular feel
- An abnormal response to being touched, for example, a haircut may trigger a meltdown. The child may be especially sensitive to unexpected touch, like tickling
Parents may worry about the process of having their child evaluated for sensory issues and somatosensation deficits, especially as many kids on the spectrum hate unfamiliar situations. Many occupational therapists assess children through a play session, which could actually be fun for the child.
Treatment for somatosensation deficits
Occupational therapists may suggest somatosensory stimulation intervention for your child on the spectrum. A literature review of somatosensory stimulation intervention for children with autism found promising results, but because more studies are needed the authors were cautious about such treatments (Thompson-Hodgetts & Hodgetts, 2008).
The above mentioned review examined interventions like massage therapy, weighted vests, pressure vests and gloves, and also arm splints and pressure arm wrapping (Thompson-Hodgetts & Hodgetts, 2008). The authors ended the review with an appeal to clinicians and researchers to systematically investigate the effects of somatosensory stimulation.
Even though most therapeutic interventions for somatosensation deficits still need backing from research, many parents provide anecdotal evidence of tactile sensitivity decreasing with interventions like weighted vests and blankets. A sensory processing disorder can disrupt a child’s life in serious ways, therefore, therapy options like deep touch therapy (or deep pressure therapy) may be worth exploring.
A somatosensory gateway to understanding autism
For all the hardship brought on by somatosensory deficits, wouldn’t it be remarkable if an exploration of this sense led to a better understanding of autism? Dr. Lauren Orefice was named the grand prize winner of The Eppendorf and Science Prize for Neurobiology in 2019 for her research that shows that peripheral somatosensory neurons can shape some behaviors associated with autism.
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Dr. Orifice added a new dimension to autism understanding with this research that shows how neurons outside the brain (the ones that control the sense of touch) can alter brain function. Her research, in mouse models, demonstrates that somatosensory neurons could be targeted in future therapeutic interventions for autism symptoms.
A premise that was explored in this research (Orefice et al., 2019) was the overreactivity of autistic individuals to light touch. Dr. Orifice’s research could create a therapeutic strategy targeting somatosensory neurons, with the potential to treat tactile overreactivity.
For autistic children who often deal with people dismissing their sensory issues as being “just oversensitive”, Dr. Orifice’s research may be especially encouraging.
References:
Büyüktaşkın, Dicle & Iseri, Elvan & Guney, Esra & Gunendi, Zafer & Cengiz, Bülent. (2021). Somatosensory Temporal Discrimination in Autism Spectrum Disorder. Autism Research. 14. 10.1002/aur.2479.
Cascio, C. J., Moana-Filho, E. J., Guest, S., Nebel, M. B., Weisner, J., Baranek, G. T., & Essick, G. K. (2012). Perceptual and neural response to affective tactile texture stimulation in adults with autism spectrum disorders. Autism research : official journal of the International Society for Autism Research, 5(4), 231–244. https://doi.org/10.1002/aur.1224.
Dellapiazza, F., Michelon, C., Oreve, M. J., Robel, L., Schoenberger, M., Chatel, C., Vesperini, S., Maffre, T., Schmidt, R., Blanc, N., Vernhet, C., Picot, M. C., Baghdadli, A., & ELENA study group (2020). The Impact of Atypical Sensory Processing on Adaptive Functioning and Maladaptive Behaviors in Autism Spectrum Disorder During Childhood: Results From the ELENA Cohort. Journal of autism and developmental disorders, 50(6), 2142–2152. https://doi.org/10.1007/s10803-019-03970-w.
Jacobs K.M. (2011) Somatosensory System. In: Kreutzer J.S., DeLuca J., Caplan B. (eds) Encyclopedia of Clinical Neuropsychology. Springer, New York, NY. https://doi.org/10.1007/978-0-387-79948-3_359.
Leekam, S. R., Nieto, C., Libby, S. J., Wing, L., & Gould, J. (2007). Describing the sensory abnormalities of children and adults with autism. Journal of autism and developmental disorders, 37(5), 894–910. https://doi.org/10.1007/s10803-006-0218-7
Orefice, L. L., Mosko, J. R., Morency, D. T., Wells, M. F., Tasnim, A., Mozeika, S. M., Ye, M., Chirila, A. M., Emanuel, A. J., Rankin, G., Fame, R. M., Lehtinen, M. K., Feng, G., & Ginty, D. D. (2019). Targeting Peripheral Somatosensory Neurons to Improve Tactile-Related Phenotypes in ASD Models. Cell, 178(4), 867–886.e24. https://doi.org/10.1016/j.cell.2019.07.024.
Thompson-Hodgetts, Sandra & Hodgetts, William. (2008). Somatosensory Stimulation Interventions for Children with Autism: Literature Review and Clinical Considerations. Canadian journal of occupational therapy. Revue canadienne d’ergothérapie. 74. 393-400. 10.2182/cjot.07.013.
