Axonal deficits in young adults with High Functioning Autism and their impact on processing speed

Area of Science:

• Neuroimaging
• Neuroscience
• Biomedical Engineering

Background:

• Autism Spectrum Disorder (ASD) is associated with white matter deficits, but findings from Diffusion Tensor Imaging (DTI) are inconsistent.
• Previous studies using DTI reported reduced fractional anisotropy (FA) and increased mean diffusivity (MD) in ASD, with unclear physiological causes.
• Understanding white matter alterations in ASD is crucial for diagnosis and intervention.

Purpose of the Study:

• To characterize white matter deficits in High-Functioning Autism (HFA) using advanced Diffusional Kurtosis Imaging (DKI).
• To investigate the diagnostic utility of compartment-specific diffusion metrics and their association with processing speed.
• To differentiate intra-axonal and extra-axonal white matter compartments in HFA.

Main Methods:

• Employed DKI and a two-compartment diffusion model to analyze white matter microstructure.
• Measured Axonal Water Fraction (faxon) reflecting axonal caliber and density, and compartment-specific diffusivities.
• Compared 16 young male adults with HFA and 17 typically developing controls (TDC), examining correlations with processing speed.

Main Results:

• Significantly decreased faxon observed in HFA across major white matter tracts (corpus callosum, cortico-spinal, longitudinal, and fronto-occipital fasciculi).
• Reduced intra-axonal diffusivity (Daxon) found in some regions; decreased axial extra-axonal diffusivity (ADextra) noted in the genu of the corpus callosum.
• Decreased faxon and Daxon correlated with reduced processing speed; faxon metrics showed high accuracy in discriminating HFA from TDC.

Conclusions:

• Findings suggest altered axonal microstructure in young adults with HFA, associated with impaired processing speed.
• Compartment-specific diffusion metrics enhance specificity and sensitivity for detecting white matter deficits in ASD.
• DKI and advanced modeling offer a promising approach for understanding and diagnosing white matter abnormalities in ASD.