Age-related differences in axon pruning and myelination may alter neural signaling in autism spectrum disorder

The temporal lobe exhibits atypical patterns of white matter development in ASD. In neurotypical individuals, decreased axon density in SWM with age reflects effective neural pruning and refinement of local and short-range connectivity. In contrast, individuals with ASD maintain a high density of small-diameter axons in STG SWM, suggesting reduced pruning that results in local overconnectivity. Moreover, myelin thickness in SWM does not increase with age in ASD, implying reduced efficacy of neurotransmission. These alterations in white matter ultrastructure may contribute to the atypical connectivity and neural communication observed in ASD across the lifespan.