Restriction Spectrum Imaging As a Potential Measure of Cortical Neurite Density in Autism.
Autism postmortem studies have shown various cytoarchitectural anomalies in cortical and limbic areas including increased cell packing density, laminar disorganization, and narrowed minicolumns. However, there is little evidence on dendritic and axonal organization in ASD. Recent imaging techniques have the potential for non-invasive,in vivostudies of small-scale structure in the human brain, including gray matter. Here, Restriction Spectrum Imaging (RSI), a multi-shell diffusion-weighted imaging technique, was used to examine gray matter microstructure in 24 children with ASD (5 female) and 20 matched typically developing (TD) participants (2 female), ages 7-17 years. RSI extends the spherical deconvolution model to multiple length scales to characterize neurite density (ND) and organization. Measures were examined in 48 cortical regions of interest per hemisphere. To our knowledge, this is the first time that a multi-compartmental diffusion model has been applied to cortical gray matter in ASD. The ND measure detected robust age effects showing a significant positive relationship to age in all lobes except left temporal when groups were combined. Results were also suggestive of group differences (ASD<TD) in anterior cingulate, right superior temporal lobe and much of the parietal lobes, but these fell short of statistical significance. For MD, significant group differences (ASD>TD) in bilateral parietal regions as well as widespread age effects were detected. Our findings support the value of multi-shell diffusion imaging for assays of cortical gray matter. This approach has the potential to add to postmortem literature, examining intracortical organization, intracortical axonal content, myelination, or caliber. Robust age effects further support the validity of the ND metric forin vivoexamination of gray matter microstructure in ASD and across development. While diffusion MRI does not approach the precision of histological studies,in vivoimaging measures of microstructure can complement postmortem studies, by allowing access to large sample sizes, a whole-brain field of view, longitudinal designs, and combination with behavioral and functional assays. This makes multi-shell diffusion imaging a promising technique for understanding the underlying cytoarchitecture of the disorder.
Brain Development Imaging Laboratory, Department of Psychology, San Diego State University San Diego, CA, USA.
Ruth A
RA
Carper
School of Medicine, University of California San Diego La Jolla, CA, USA.
Jeffrey M
JM
Treiber
Multimodal Imaging Laboratory, Department of Radiology, University of California San Diego La Jolla, CA, USA.
Nathan S
NS
White
Brain Development Imaging Laboratory, Department of Psychology, San Diego State University San Diego, CA, USA.
Jiwandeep S
JS
Kohli
Brain Development Imaging Laboratory, Department of Psychology, San Diego State University San Diego, CA, USA.
Ralph-Axel
RA
Müller
DTI; MRI; autism; cerebral cortex; connectivity; diffusion; gray matter; neurite