Many individuals with autism spectrum disorder (ASD) exhibit motor difficulties, but it is unknown whether manual motor skills improve, plateau, or decline in ASD in the transition from childhood into adulthood. Atypical development of manual motor skills could impact the ability to learn and perform daily activities across the life span. This study examined longitudinal grip strength and finger tapping development in individuals with ASD (n=90) compared to individuals with typical development (n=56), ages five to 40 years old. We further examined manual motor performance as a possible correlate of current and future daily living skills. The group with ASD demonstrated atypical motor development, characterized by similar performance during childhood but increasingly poorer performance from adolescence into adulthood. Grip strength was correlated with current adaptive daily living skills, and Time 1 grip strength predicted daily living skills eight years into the future. These results suggest that individuals with ASD may experience increasingly more pronounced motor difficulties from adolescence into adulthood and that manual motor performance in ASD is related to adaptive daily living skills.

Mounting evidence suggests that poorer motor skills may be related to more severe autism symptoms. This study investigated if atypical white matter microstructure in the brain mediated the relationship between motor skills and ASD symptom severity. Sixty-seven males with ASD and 42 males with typical development (5-33 years old) completed a diffusion tensor imaging scan and measures of grip strength, finger tapping, and autism symptom severity. Within the ASD group, weaker grip strength predicted more severe autism symptoms. Fractional anisotropy of the brainstem's corticospinal tract predicted both grip strength and autism symptom severity and mediated the relationship between the two. These findings suggest that brainstem white matter may contribute to autism symptoms and grip strength in ASD.

Heightened auditory sensitivity and atypical processing of sounds by the brain are common in autism. Functional studies that measure brain activity suggest abnormal neural response to sounds, yet the development underlying atypical sound processing in autism is unknown. We examined the growth of the first cortical area of the brain to process sound, the primary auditory cortex, also known as Heschl’s gyrus. Volume of Heschl’s gyrus gray and white matter was measured using structural MRI in 40 children and adolescents with autism and 17 typically developing participants. Up to three time points of volumetric brain data, collected on average every 2.5 years, were examined from individuals 3-12 years of age at their first scan. Our study is the first to examine volumetric changes during childhood and adolescence in Heschl’s gyrus longitudinally, or in the same individuals over time. Consistent with previous studies using only one time point of data, no differences between the participant groups were found in Heschl’s gyrus gray matter volume. However, reduced longitudinal growth of Heschl’s gyrus gray matter volume was found in the right hemisphere in autism. Reduced longitudinal white matter growth in the left hemisphere was found in the right-handed autism participants. Atypical growth of Heschl’s gyrus white matter volume was found bilaterally in the autism individuals with a history of delayed onset of spoken language. Heightened reported sensitivity to sounds, obtained from the Sensory Profile, was associated with reduced gray matter volume growth in the right hemisphere. Our longitudinal analyses revealed dynamic gray and white matter changes in Heschl’s gyrus throughout childhood and adolescence in both typical development and autism.

Microstructure of the thalamus, a key sensory and motor brain area, appears to develop differently in individuals with autism spectrum disorder (ASD). Microstructure is important because it informs us of the density and organization of different brain tissues. During childhood, thalamic microstructure was distinct in the ASD group compared to the typically developing group. However, these group differences appeared to narrow with age, suggesting that the thalamus continues to dynamically change in ASD into adulthood.