The study by Chang et al, published online in PLOS on July 30, uses new sophisticated tract imaging to show impaired white matter microstructure. In this study, three groups were compared: 15 ASD boys, 16 SPD boys, and 23 neurotypical children (“typically developing children, TDC”, the authors call them. The authors are interested in demonstrating that SPD are a distinct diagnostic class—not yet officially categorized. They recognized that many more children have sensory processing difficulties than would be considered Autistic Spectrum. While 90% of ASD children have atypical sensory behaviors, it is important to recognize those with SPD but not ASD. As the authors state, “With over 1% of children in the USA carrying an ASD label and reports of 5–16% of children in the USA having sensory processing difficulties, it is important to define the neural underpinnings of these conditions and to delineate the areas of overlap and the areas of divergence.”
In a press release from UCSF, Elysa Marco MD, cognitive and behavioral child neurologist at UCSF Benioff Children’s Hospital San Francisco and the study’s corresponding author said, “One of the most striking new findings is that the children with SPD show even greater brain disconnection than the kids with a full autism diagnosis in some sensory-based tracts. However, the children with autism, but not those with SPD, showed impairment in brain connections essential to the processing of facial emotion and memory.”
The UCSF press release is available at http://www.ucsf.edu/news/2014/07/116196/kids-autism-and-sensory-processing-disorders-show-differences-brain-wiring Note this is also where I obtained the photo used in this blog.
In their discussion, Chang and colleagues discussed the far-reaching implications of their study. They showed in their white matter diffusion tensor imaging (DTI) that, “perhaps the most striking finding is that, relative to the control group, the ASD cohort shows reduced structural connectivity in the fusiform gyrus connections to the amygdala and hippocampus, whereas children with SPD do not. These white matter pathways are thought to facilitate facial emotional processing, a core feature of autism and the domain of clinical divergence for ASD versus SPD.”
For further contrast, they bring in the neuro-genetic disturbance, Williams Syndrome. People with that condition, have intellectual deficits + distinct “elfin” features + cardiac developmental dysfunction—but notably, most individuals with Williams syndrome are highly verbal relative to their IQ, and are overly sociable, having what has been described as a “cocktail party” type personality [Wikipedia: Lashkari, Askan; Smith, Andrew & Graham, John (1 May 1999). “Williams-Beuren Syndrome: An Updated Review for the Primary Physician”. Clinical Pediatrics 38 (4): 189–208.]. Chang et al remark that the network deficits through the fusiform-amygdala-hippocampus system they have demonstrated in ASD are in stark contrast to the network enhancements in Williams syndrome patients. “Individuals with Williams Syndrome show a social phenotype that is in some ways opposite to the autism phenotype with increased attention to faces and abundant social interest and drive. It is thus worthwhile to consider social cognition, or facial emotion recognition specifically, as a continuous trait that might map directly to connectivity of the fusiform tract to limbic structures.
Somewhat technically, but of importance, they continue later in the paper, “there are however additional farther reaching implications for fusiform connectivity disruptions with regard to language development. A theoretical model of audiovisual affective speech perception begins with input to primary auditory and visual cortex. The input module feeds information to the fusiform gyrus as well as the integration module of the superior and middle temporal cortex. The primary sensory cortices as well as the fusiform gyrus are reciprocally connected to the amygdala and insula, which comprise the emotion module that guides emotional relevance and may facilitate the rapid recruitment of limbic brain regions by visual inputs. Additional contextual information is brought in through connections with the memory module, including the hippocampus and parahippocampal gyrus. This framework is useful in considering how autism social communication deficits may map to neuroanatomic networks.”
Disruption in Sensory Pathways but Divergent Connectivity in Social-Emotional Pathways
- Yi-Shin Chang ¶,
- Julia P. Owen ¶,
- Shivani S. Desai,
- Susanna S. Hill,
- Anne B. Arnett,
- Julia Harris,
- Elysa J. Marco mail,
- Pratik Mukherjee
- Published: July 30, 2014 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0103038