Section: New Results

Clinical and Neurocognitive Applications of Diffusion MRI

Plasticity of left perisylvian white-matter tracts is associated with individual differences in math learning brain structure and function

Participants : Dietsje Jolles [Stanford University & Leiden University] , Demian Wassermann, Ritika Chokhani [Stanford University] , Jennifer Richardson [Stanford University] , Caitlin Tenison [Stanford University] , Roland Bammer [Stanford University] , Lynn Fuchs [Vanderbilt University] , Kaustubh Supekar [Stanford University] , Vinod Menon [Stanford University] .

Plasticity of white matter tracts is thought to be essential for cognitive development and academic skill acquisition in children. However, a dearth of high-quality diffusion tensor imaging (DTI) data measuring longitudinal changes with learning, as well as methodological difficulties in multi-time point tract identification have limited our ability to investigate plasticity of specific white matter tracts. Here, we examine learning- related changes of white matter tracts innervating inferior parietal, prefrontal and temporal regions following an intense two-month math tutoring program. DTI data were acquired from 18 third grade children, both before and after tutoring. A novel fiber tracking algorithm based on a White Matter Query Language (WMQL) was used to identify three sections of the superior longitudinal fasciculus (SLF) linking frontal and parietal (SLF-FP), parietal and temporal (SLF-PT) and frontal and temporal (SLF-FT) cortices, from which we created child-specific probabilistic maps. The SLF-FP, SLF-FT, and SLF-PT tracts identified with the WMQL method were highly reliable across the two time points and showed close correspondence to tracts previously described in adults. Notably, individual differences in behavioral gains after two months of tutoring were specifically correlated with plasticity in the left SLF-FT tract. Our results extend previous findings of individual differences in white matter integrity, and provide important new insights into white matter plasticity related to math learning in childhood. More generally, our quantitative approach will be useful for future studies examining longitudinal changes in white matter integrity associated with cognitive skill development.

This work has been published in [16]

Prefrontal cortex white matter tracts in prodromal Huntington disease

Participants : Joy T. Matsui [Iowa University] , Jatin G. Vaidya [Iowa University] , Demian Wassermann [Iowa University] , Regina Eunyoung Kim [Iowa University] , Vincent A. Magnotta [Iowa University] , Hans J. Johnson [Iowa University] , Jane S. Paulsen [Iowa University] , Predict-Hd Investigators And Coordinators Of The Huntington Study Group [NIH] .

Huntington disease (HD) is most widely known for its selective degeneration of striatal neurons but there is also growing evidence for white matter (WM) deterioration. The primary objective of this research was to conduct a large-scale analysis using multi-site diffusion-weighted imaging (DWI) tractography data to quantify diffusivity properties along major prefrontal cortex WM tracts in prodromal HD. Fifteen international sites participating in the PREDICT-HD study collected imaging and neuropsychological data on gene-positive HD subjects without a clinical diagnosis (i.e. prodromal) and gene-negative control subjects. The anatomical prefrontal WM tracts of the corpus callosum (PFCC), anterior thalamic radiations (ATR), inferior fronto-occipital fasciculi (IFO), and uncinate fasciculi (UNC) were identified using streamline tractography of DWI. Within each of these tracts, tensor scalars for fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity coefficients were calculated. We divided prodromal HD subjects into three CAG-age product (CAP) groups having Low, Medium, or High probabilities of onset indexed by genetic exposure. We observed significant differences in WM properties for each of the four anatomical tracts for the High CAP group in comparison to controls. Additionally, the Medium CAP group presented differences in the ATR and IFO in comparison to controls. Furthermore, WM alterations in the PFCC, ATR, and IFO showed robust associations with neuropsychological measures of executive functioning. These results suggest that long-range tracts essential for cross-region information transfer show early vulnerability in HD and may explain cognitive problems often present in the prodromal stage.

This work has been published in [17]