Socioeconomic status is unrelated to T1w/T2w myelin content in the Human Connectome Project in Development

Growing evidence indicates that brain development varies as a function of family socioeconomic status (SES). Numerous studies have demonstrated that children from low-SES backgrounds have thinner cortex than children from higher-SES backgrounds. This may reflect exaggerated pruning of underutilized synaptic connections, increases in cortical myelination, or both. A recent study in a large developmental sample found widespread associations between lower SES and greater cortical T1w/T2w ratio thought to be an indirect proxy for cortical myelin. We evaluated the association of SES with cortical T1w/T2w ratio as a function of age in the Human Connectome Project in Development sample of 989 youth aged 8-21 years. We observed no associations between SES and T1w/T2w myelin that were significant after corrections for multiple comparisons at the region, network, or whole-brain level. We discuss some potential methodological sources of inconsistency between this and the previous study examining the same question. While the question of whether SES may influence cortical myelin development remains, these null results—when considered alongside frequently observed associations between SES and cortical thickness—may indicate that the association between SES and cortical development is characterized more by increased pruning of underutilized synaptic connections than by differences in cortical myelination.