Strong negative reactions to everyday stimuli, such as the feeling of clothes on skin or the sounds of ambient noises, are uniquely linked to anxiety and autism, and not to other neuropsychiatric conditions such as attention-deficit/hyperactivity disorder, according to a new study.
These responses, termed sensory over-responsivity, have long been part of the diagnostic criteria for autism. This trait occurs in about 15 to 20 percent of children in the general population and is overrepresented in various psychiatric conditions, including anxiety disorders, ADHD and obsessive-compulsive disorder.
Prior studies have primarily assessed neuropsychiatric conditions in isolation—for example, by comparing a group in one diagnostic category with a control group, says Rebecca Schwarzlose, assistant professor of psychiatry at Washington University School of Medicine in St. Louis. But autism, anxiety and other neurodevelopmental conditions often co-occur. Sensory over-responsivity may be the result of this overlap in many cases, rather than being linked to the condition in question, according to the new work, published last month in the Journal of the American Academy of Child & Adolescent Psychiatry.
Schwarzlose and her colleagues brought together five independent, previously collected datasets containing a mix of community samples—people randomly selected from the general public—and samples containing a high proportion of autistic people. In total, they analyzed 15,728 children aged 6 to 18 years.
Sensory over-responsivity was associated with the traits of all six psychiatric conditions the team assessed in analyses that considered one diagnosis at a time. But a different picture emerged when the researchers analyzed all the traits simultaneously: Sensory over-responsivity appeared to be uniquely associated with anxiety symptoms and autism traits. The links with other conditions, such as ADHD, were reduced to small effect sizes or became insignificant.
“It’s a huge strength to be able to look at sensory over-responsivity in such a large sample,” says Grace Baranek, professor of occupational science and occupational therapy at the University of Southern California, who was not involved in the work. “We haven’t had the capabilities or the resources, necessarily, to kind of merge these datasets in the way that they were able to do.”
T
he findings confirm those in previously reported, smaller studies and provide additional evidence that over-responsivity to sensory stimuli may have cascading effects on neurodevelopment, Baranek says. But the findings don’t necessarily rule out a link between sensory processing differences and ADHD, she adds.A key limitation of this study is that it measured sensory over-responsivity based on a single yes/no questionnaire item that asked parents if their child seemed overly sensitive to sounds, textures or smells, she says.
Schwarzlose says that in unpublished work, she and her colleagues have endeavored to use a more objective measure, assessing how children react to sensory stimuli in the lab while playing games. Those observations have aligned more closely with parent reports of sensory over-responsivity in everyday life than with children’s reports, which she says gave her team greater confidence in their published findings.
But sensory over-responsivity is complex and encompasses many factors, including how a person experiences a sensation and their behavioral responses. Sensory under-responsivity, which other studies have linked to ADHD and autism, should also be considered, Baranek says.
Shulamite Green, associate professor of developmental psychology at the University of California, Los Angeles, who was not involved in this work (but is one of Schwarzlose’s former supervisors), agrees that the case for ADHD and sensory over-responsivity—which she has seen frequently overlap in the clinic—is not closed.
However, the new study suggests that perhaps the mechanisms underlying sensory over-responsivity—such as its biological underpinnings or how it develops over time—are more similar in people with anxiety and autism than in those with ADHD, Green says. “We see these differences in sensory reactivity across all of these different groups of kids.” But what hasn’t been well understood is whether these differences develop in the same way, she adds.
S
chwarzlose and her colleagues also analyzed neuroimaging data, which had been collected using resting-state functional MRI, in a subset of 9,197 children. They found that sensory over-responsivity was linked to reduced functional connectivity between the cingulo-parietal network, which is involved in memory, and both the left and right caudate nuclei, which are involved in bridging sensory inputs and behavior.These findings are preliminary, Schwarzlose says. Some of the effect sizes are small and do not appear to be significant in a smaller dataset the researchers used to replicate their findings, she and her co-investigators note. The team is now looking more closely at these brain circuits using fMRI studies in which participants’ brains are scanned while they are exposed to certain sensory stimuli.
It is still “very early days” for this research, but the hope is that this work will help the field better understand what drives a trait that can be debilitating to those who experience it, Schwarzlose says. “We know that sensory over-responsivity can be really impairing. It is pretty universally hated by people who experience it.”
