Somatosensation

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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.

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.

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.

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.

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.

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.

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.

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.

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.