Reduced asymmetry of the hand knob area and decreased sensorimotor u-fiber connectivity in middle-aged adults with autism

Individuals with autism spectrum disorder (ASD) frequently present with impairments in motor skills (e.g., limb coordination, handwriting and balance), which are observed across the lifespan but remain largely untreated. Many adults with ASD may thus experience adverse motor outcomes in aging, when physical decline naturally occurs. The 'hand knob' of the sensorimotor cortex is an area that is critical for motor control of the fingers and hands. However, this region has received little attention in ASD research, especially in adults after midlife. The hand knob area of the precentral (PrChand) and postcentral (PoChand) gyri was semi-manually delineated in 49 right-handed adults (25 ASD, 24 typical comparison [TC] participants, aged 41-70 years). Using multimodal (T1-weighted, diffusion-weighted, and resting-state functional) MRI, we examined the morphology, ipsilateral connectivity and laterality of these regions. Correlations between hand knob measures with motor skills and autism symptoms, and between structural and functional connectivity measures were also investigated. The right PrChand volume was greater, and typical leftward laterality of PrChand and PoChand volume was lower in the ASD than the TC group. Furthermore, we observed increased mean diffusivity of the right PoC-PrChand u-fibers in the ASD group. In the ASD group, right PoC-PrChand u-fiber volume was negatively associated with current autism severity, and positively associated with right PoC-PrChand functional connectivity (FC). Correlations of hand knob measures were observed with manual dexterity and coordination skills but did not survive multiple comparisons correction. Our findings suggest decreased morphological laterality and u-fiber connectivity of the sensorimotor network involved in hand function in middle-aged adults with ASD. The altered morphology may relate to atypical functional asymmetries found in ASD earlier in life, but additionally, could reflect an overreliance on right hemisphere motor circuits over time. The right PoC-PrChand u-fibers may underlie compensatory self-regulation of unwanted core motor behaviors seen in ASD.

Fiber Connectivity Density Mapping in End-stage Renal Disease Patients: A Preliminary Study

Abnormal brain structural connectivity of end-stage renal disease (ESRD) is associated with cognitive impairment. However, the characteristics of cortical structural connectivity have not been investigated in ESRD patients. The current study aimed to investigate the structural connectivity of the entire cerebral cortex in ESRD patients. Twenty-five ESRD patients and 20 healthy controls were recruited for this study; all participants underwent diffusion tensor imaging and high-resolution T1-weighted imaging scanning. Fiber connectivity density (FiCD) mapping was performed to calculate structural connectivity of the whole cortex, and between-group differences were compared in a vertexwise manner. We also tested the associations between FiCD changes and clinical information using Pearson correlation analysis. The results demonstrated that the mean global FiCD value was significantly decreased in ESRD patients compared with that of HCs. Notably, FiCD values were significantly changed (decreased or increased) in certain cortical regions, which mainly involved the bilateral dorsolateral prefrontal cortex (DLPFC), inferior parietal, lateral temporal and middle occipital cortex (P < 0.01 with Monte Carlo correction). Moreover, in ESRD patients, the increased FiCD values in the right middle frontal gyrus were negatively correlated with serum creatinine (r=-0.473, p = 0.017) and urea levels (r=-0.511, p = 0.009). The increased FiCD values in the left middle frontal gyrus were negatively correlated with dialysis duration (r=-0.577, p = 0.003) and parathyroid hormone (PTH) levels (r=-0.552, p = 0.004). Our results suggested that ESRD patients exhibited extensive impaired cortical structural connectivity. And there may be a compensation mechanism of cortical structural recombination that plays a role in the way the brain adapts to maintain optimal network function. Moreover, serum creatinine, urea and PTH levels may be risk factors for brain structural network decompensation in ESRD patients.

Mapping Short Association Fibers in the Early Cortical Visual Processing Stream Using In Vivo Diffusion Tractography

Short association fibers (U-fibers) connect proximal cortical areas and constitute the majority of white matter connections in the human brain. U-fibers play an important role in brain development, function, and pathology but are underrepresented in current descriptions of the human brain connectome, primarily due to methodological challenges in diffusion magnetic resonance imaging (dMRI) of these fibers. High spatial resolution and dedicated fiber and tractography models are required to reliably map the U-fibers. Moreover, limited quantitative knowledge of their geometry and distribution makes validation of U-fiber tractography challenging. Submillimeter resolution diffusion MRI—facilitated by a cutting-edge MRI scanner with 300 mT/m maximum gradient amplitude—was used to map U-fiber connectivity between primary and secondary visual cortical areas (V1 and V2, respectively) in vivo. V1 and V2 retinotopic maps were obtained using functional MRI at 7T. The mapped V1–V2 connectivity was retinotopically organized, demonstrating higher connectivity for retinotopically corresponding areas in V1 and V2 as expected. The results were highly reproducible, as demonstrated by repeated measurements in the same participants and by an independent replication group study. This study demonstrates a robust U-fiber connectivity mapping in vivo and is an important step toward construction of a more complete human brain connectome.