Structural Determinants of Signal Speed: A Multimodal Investigation of Face Processing in Autism Spectrum Disorder.

Face perception is fundamental to social cognition and often disrupted in autism. However, the neurological basis for this disrupted face perception and the mechanisms underlying altered electrophysiological signaling in autism, such as increased latency of the N170-an electrophysiological marker of face processing, remain unknown. Here, we leverage multimodal neuroimaging in autistic adolescents to establish a link between MRI-measured axonal microstructure within the face processing network and EEG-measured N170 latency. We demonstrate that a novel metric of axonal signal transit time derived from axonal diameter, myelination, and length-estimated axonal latency (EAL)-predicts N170 latency during face processing. Moreover, we demonstrate that individuals with and without autism rely upon different pathways, providing a structural account for autism-related face processing differences. By establishing this relationship between EEG-based electrical function and MRI-based axonal microstructure, we provide a non-invasive, spatially-detailed estimate of neuronal processing speed that can inform understanding of brain function, development, and disorder.