Brainstem White Matter Predicts Individual Differences in Manual Motor Difficulties and Symptom Severity in Autism

Abstract

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.

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“…2, Part D), in their autistic participants, between the degree of abnormality in the arcuate and uncinate fasciculi and childhood language symptoms as measured by the Autism Diagnostic Interview-Revised (Le Couteur et al, 2003). At the behavioural level, relationships between movement deficits and autistic symptom severity are well documented in our review (MacDonald, Lord, & Ulrich, 2014;Papadopoulos et al, 2012;Stevenson, Lindley, & Murlo, 2017;Travers et al, 2015Travers et al, , 2013Uljarevic, Hedley, Alvares, Varcin, & Whitehouse, 2017;Colombo-Dougovito & Reeve, 2017 are an exception, but a questionable one due to their methods).…”

“…In a small sample, Hanaie et al (2013) documented abnormalities in the cerebellum, in autistic children, which predicted poorer motor skills and poorer ball skills (these authors did not measure gait). Travers et al (2015) found cerebellar abnormalities to predict tapping speed in autistic children and adolescents. As previously noted, functional communication between the cerebellum and the rest of the motor system was reported to be compromised .…”

“…9 These are supplemented by theoretical accounts of ASC in terms of brain-wide dysfunction characterized by 'noisy' or dysfunctional neural communication (Belmonte et al, 2004;Minshew & Goldstein, 1998;Rubenstein & Merzenich, 2003). In autistic children and adolescents, Travers et al (2015) indeed found reduced structural integrity of the long-ranging corticospinal tract of fibres which arise from motor cortex and travel to the brainstem; this related to poorer grip strength and finger tapping, and to autistic symptomatology. Hanaie et al (2016) also found correlations with poorer motor performance and reduced integrity in parts of the brainstem which connect to the somatosensory cortex through the thalamus, which connect the cerebellum to the brainstem, and the superior longitudinal fasciculus connecting the supramarginal gyrus and inferior parietal sulcus with frontal motor systems.…”

“…Precisely 49 studies comparing ASC and typically-developing (TD) control groups answer this question in the affirmative. The more methodologically rigorous studies, those which a) either matched for chronological and/or mental age and/or IQ or b) controlled for these in their analyses, and c) had more sizeable groups (>30 per group) demonstrate that motor impairments occur more often than might be expected in TD children (AbuDahab, Skidmore, Holm, Rogers, & Minshew, 2013;Ament et al, 2015;Dewey, Cantell, & Crawford, 2007;Dowell, Mahone, & Mostofsky, 2009;Duffield et al, 2013;Dziuk et al, 2007;Floris et al, 2016;Sumner, Leonard, & Hill, 2016;Travers et al, 2015Travers et al, , 2016. A meta-analysis of 41 studies confirmed that, despite substantial variation, effect sizes are large with TD participants significantly outperforming individuals with autism in motor coordination, arm movements, gait and postural stability (Fournier, Hass, Naik, Lodha, & Cauraugh, 2010), and that these effects did not seem affected by publication bias.…”

“…Other studies of kinematics in very basic arm movements and reaching and grasping reveal differences between autistic and TD participants (Campione, Piazza, Villa, & Molteni, 2016;Cook, Blakemore, & Press, 2013). Use of more traditional neuropsychological tests reflect poorer performance in the grip strength (Abu-Dahab et al, 2013;Hardan et al, 2003;Travers et al, 2015Travers et al, , 2016, finger tapping (Abu-Dahab et al, 2013;Duffield et al, 2013;Hardan et al, 2003;Travers et al, 2016) and pegboard tasks (Abu-Dahab et al, 2013;Ament et al, 2015;Barbeau, Meilleur, Zeffiro, & Mottron, 2015;Duffield et al, 2013;Hardan et al, 2003). These tests ascend in difficulty, primarily testing muscle strength, simple motor coordination and dexterity respectively.…”