Ian Fuelscher

Myelination of human brain white matter (WM) continues into adulthood following birth, facilitating connection within and between brain networks. In vivo MRI studies using diffusion weighted imaging (DWI) suggest microstructural properties of brain WM increase over childhood and adolescence. Although DWI metrics, such as fractional anisotropy (FA), could reflect axonal myelination, they are not specific to myelin and could also represent other elements of WM microstructure, for example, fibre architecture, axon diameter and cell swelling. Little work exists specifically examining myelin development. The T1w/T2w ratio approach offers an alternative non-invasive method of estimating brain myelin. The approach uses MRI scans that are routinely part of clinical imaging and only require short acquisition times. Using T1w/T2w ratio maps from three waves of the Neuroimaging of the Children’s Attention Project (NICAP) [N = 95 (208 scans); 44% female; ages 9.5–14.20 years] we aimed to investigate the developmental trajectories of brain white matter myelin in children as they enter adolescence. We also aimed to investigate whether longitudinal changes in myelination of brain WM differs between biological sex. Longitudinal regression modelling suggested non-linear increases in WM myelin brain wide. A positive parabolic, or U-shaped developmental trajectory was seen across 69 of 71 WM tracts modelled. At a corrected level, no significant effect for sex was found. These findings build on previous brain development research by suggesting that increases in brain WM microstructure from childhood to adolescence could be attributed to increases in myelin.

This study investigated sex and age differences in autistic behaviours in children with neurofibromatosis type 1 (NF1) who scored within the clinical range on the Social Responsiveness Scale - Second Edition (T score ≥ 60). Thirty-four males and 28 females (3–16 years) were assessed with the Autism Diagnostic Observation Schedule - Second Edition and Autism Diagnostic Interview - Revised. Across both measures, males exhibited greater social communication deficits relative to females. Age-related abatement of social communication difficulties was observed for males but not females. Conversely, no sex differences were found for restricted/repetitive behaviours, which were stable over time for both males and females. The findings are discussed within the context of broader neurodevelopmental considerations that are common in NF1.

Background Corpus callosum anomalies are commonly noted in autism spectrum disorder (ASD). Given the complexity of its microstructural architecture, with crossing fibers projecting throughout, we applied fixel-based analysis to probe white matter micro- and macrostructure within this region. As ASD is a neurodevelopmental condition with noted abnormalities in brain growth, age was also investigated. Methods Data for participants with (N=54) and without (N=50) ASD, aged 5-34 years, were obtained from the Autism Brain Imaging Data Exchange-II (ABIDE-II). Within each site, indices of fiber density (FD), fiber cross-section (FC), and combined fiber density and cross-section (FDC) were compared between those groups. Results Young adolescents with ASD (age = 11.19 ± 7.54) showed reduced macroscopic FC and FDC compared to age-matched neurotypical controls (age = 10.04 ± 4.40). Reduced FD and FDC was noted in a marginally older ASD (age 13.87 ± 3.15) cohort compared to matched controls (age = 13.85 ± 2.90). Among the oldest cohorts, a non-significant trend indicated reduced FD in older adolescents/young adults with ASD (age = 17.07 ± 3.56) compared to controls (age = 16.55 ± 2.95). There was a positive correlation between age and callosal mean FC and FDC in the youngest cohort. When stratified by diagnosis, this finding remained only for the ASD sample. Conclusion White matter aberration appears greatest among younger ASD cohorts. In older adolescents and young adults, less of the corpus callosum seems affected. This supports the suggestion that some early neuropathophysiological indicators in ASD may dissipate with age.

Pressure to send sexually explicit messages, or ‘sexting coercion’ is associated with adverse mental health outcomes and sexual risk behaviors. This study explores Differentiation of Self (DoS) as a potential protective factor to reduce susceptibility to sexting coercion. A convenience sample of 399 Australian participants, aged 18 to 21 years (M_age = 19.63; SD = 1.14, 68.2% women) completed an online survey measuring sexting behaviors and DoS. Women were four times more likely to send willing unwanted sexts, and seven times more likely to engage in coerced unwanted sexting than men. Participants with low DoS were four times more likely to engage in coerced unwanted sexting. DoS significantly mediated the relationship between gender and coerced unwanted sexting. Results support the proposal of a sexting coercion typology encompassing discrete sub-types of sexting coercion. Results also indicate DoS may operate as a protective factor for young people in Australia, reducing compliance with sexting when coerced.

While motivation for physical activity (PA) and PA participation have been linked, research on the relationship between motivation for PA and mental health outcomes is scant, with studies involving children largely underrepresented. Grounded in self-determination theory, this cross-sectional study aimed to determine whether autonomous motivation versus external motivation (a form of controlled motivation) for PA is associated with fewer emotional and behavioural difficulties and higher levels of PA in children. A sample of 87 children (aged 8–12 years) were recruited from five primary schools in Victoria, Australia. An adapted version of the Behavioural Regulation in Exercise Questionnaire (BREQ) was used to measure motivation for PA and structured parent-report questions were used to assess moderate-to-vigorous PA (MVPA) levels. Parents also completed the Strengths and Difficulties Questionnaire (SDQ) to measure children’s emotional and behavioural difficulties. Children’s autonomous motivation was associated with fewer emotional and behavioural difficulties (β = −0.25, p = 0.038) and higher levels of MVPA (β = 0.24, p = 0.014). These results indicate autonomous motivation is associated with improved mental health outcomes and higher levels of PA in children. Thus, PA interventions that promote autonomous motivation may enhance children’s mental health compared to interventions that promote mainly controlled forms of motivation.