Autism, SPD Hit Different Brain Areas

Children with sensory processing disorder (SPD), and children with autism, both possess fewer white matter connections--but in very different brain regions, say University of California San Francisco (UCSF) researchers.

Their PLOS One study is the first to compare—and find potentially critical differences in—brain connectivity in autism, versus sensory processing disorder, versus controls.

The study could help establish SPD as a distinct neuropathology, letting thousands of children get the right help, proponents believe.

“This is really important work,” said Sophie Molholm in an email to Bioscience Technology. An Albert Einstein College pediatric neuroscientist, Molholm was not involved in the paper. “There are very few studies on SPD, and we don’t yet understand what brain regions and neural pathways are implicated in the highly disruptive sensory processing issues that are experienced by individuals” with the disorder. The UCSF group “makes significant headway,” Molholm said.

“Differentiating two diagnostic groups from each other and a control group, based on white matter microstructure pathology that correlates with sensory-based behavior, is an astonishing breakthrough,” said Temple University sensory processing expert Moya Kinnealey, also by email. Kinnealey was also uninvolved in the study. “This meticulously researched article demonstrates sensory-based behaviors are reliably traceable to white matter differences.”

Building on earlier work

The new research builds on the UCSF group’s 2013 study, which found boys with SPD have quantifiable regional differences in brain structure compared to typical boys. That study attracted enormous interest from parents and clinicians worldwide. Articles on it attracted thousands of hits for months post-publication. But while it showed a potential biological basis for SPD, other neurodevelopmental disorders weren’t compared.

SPD is tough to diagnose. More than 90 percent of autistic kids can display abnormal sensory behaviors. SPD is not yet listed in the Diagnostic and Statistical Manual of Mental Disorders.

In the new study, the USCF group found kids with SPD show a greater brain disconnection than those with autism in some sensory-based tracts. And children with autism, not SPD, had flaws in brain connections critical for processing facial emotion and memory.

“The biggest surprise for me was how very well the main results fit with our hypotheses about how ASD [autism spectrum disorders] and SPD kids would be similar, and how they would differ,” said co-author Pratik Mukherjee in an email to Bioscience.

“Two big surprises for me,” said senior author and Director of Research, Autism, and Neurodevelopment Elysa Marco, also by email. First, she said, in many sensory regions, the SPD group showed less connectivity than the ASD group. Second, she said, “there were uniquely affected tracts for the SPD and ASD groups— and the ASD group’s tracts were well-known facial emotion processing tracts. This was a really nice replication of the existing literature and different from the SPD cohort."

Kids with SPD improperly process stimulation, and can be painfully hypersensitive to sounds, sights, and touch. Easily distracted, they possess poor fine motor skills. A sound that irks one day is ignored the next. As clinicians are split over whether it is distinct from autism, kids often go without proper treatment, the UCSF group says.

DTI MRI strikes again

As in the last study, Mukherjee, an imaging expert, used diffusion tensor imaging (DTI) MRI. It follows water molecules as they slither through brains on white matter tracts. DTI reveals direction and integrity of tracts, mapping paths between regions.

The study looked at connectivity of tracts in 16 boys with SPD, 15 boys with autism and 23 “control” boys.

Both the SPD and ASD groups showed decreased connectivity in parieto-occipital tracts, areas filtering basic sensory information. Only autistic kids showed impairment in the inferior fronto-occipital fasciculi (IFOF), inferior longitudinal fasciculi (ILF), fusiform-amygdala, and the fusiform-hippocampus tracts, areas key for social-emotional processing.

A feature of autism is eye-to-eye avoidance, and difficulty “getting” faces. Impairment in this area of brain connectivity distinguished the study’s ASD and SPD groups. The more difficulty kids had socially, the more those regions were disconnected.

And kids with SPD showed less connectivity in basic perception and integration tracts connecting for the auditory, visual, and tactile systems involved in sensory processing.

The finds show “it is crucial to understand and treat sensory processing issues in developmental disorders,” said Molholm. “In ASD, difficulties with communication and social interactions are often the major focus of treatment.” But in ASD, in the study, “there is disruption of pathways implicated in SPD… This suggests treatment of sensory dysregulation might be essential to alleviating majorly disruptive symptoms of ASD.”

At Albert Einstein, Molholm and neuroscientist John Foxe are also looking at neural mechanisms underlying SPD, using high-density electrophysiological recordings. They see “clear differences in sensory processing and multisensory integration in SPD compared to typically developing individuals. We also see significant similarities and differences in how brain function is impacted by SPD and ASD,” Molholm said.

Kinnealey said the work “reframes several barriers to understanding ASD and SPD.” If other studies echo it, “there could be a paradigm shift.”

Disagreement

There is some disagreement. Vanderbilt University speech specialist Stephen Camarata, uninvolved in the study, emailed that the paper is “intriguing…but it will be even more interesting to see whether it is replicated. In autism, we have seen quite of number of reports showing differences that do not hold up."

Larry Desch, lead author of a 2012 American Academy of Pediatrics advisory that “at this time” clinicians avoid SPD diagnoses, said via email: “This is a small study and needs to be replicated with larger samples. I have no reason to disbelieve the results, but how practical is doing fancy MRI scans in order to ‘prove’ somebody has SPD? There still are some concerns from researchers about what is really being measured by the Sensory Profile.”

Desch said the study doesn’t detail how other diagnoses in the SPD group were excluded. “The study states ‘formal ADHD evaluations were not conducted as part of this study.’ But it reports many of those with SPD demonstrated high scores for attention issues on the Sensory Profile.”

Finally, he said, research is needed on interventions to see if they help “with whatever SPD is.”

Marco said it is “absolutely true” replication is key. She noted, however, the study is not about diagnoses, but showing neural causes of “sensory processing and cognitive differences in this group of affected children, relative to a group well-studied over time [ASD] known to have sensory differences as well.” The Sensory Profile is “a good screener for sensory differences.”

When it comes to detailing how they excluded other diagnoses in the SPD group, Marco said: “We used the Social Communication Questionnaire and the ADOS (Autism Diagnostic Observation Schedule) when there was a concern for Autism in the SPD kids, and to validate diagnosis [in ASD]. Again, this was not about labeling kids, but about finding if there are brain differences in kids with sensory processing [behavioral] differences, both those with social communication differences— ASD— and without— SPD— relative to controls.” She added: “The Sensory Profile has an ‘attention scale’ that might raise concern for attention challenges but is certainly not a formal ADHD diagnosis.”

Regarding the notion more intervention research is needed, she said, “Very true!” She is working on cognitive intervention training now.