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

Abstract

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.