Prior reports suggest that autism spectrum disorder (ASD) is associated with atypically excessive early brain growth. Recent cross-sectional studies suggest that later cortical development during adolescence/adulthood might also be aberrant, although longitudinal designs are required to evaluate atypical growth trajectories. The present study sought to examine longitudinal changes in cortical thickness and surface area among adolescents and young adults with ASD.

Two high-resolution anatomic magnetic resonance imaging scans approximately 2 years apart were acquired from 17 adolescents with ASD and 18 typically developing (TD) adolescents, matched on age (range = 14–24 years), IQ, sex ratio, and handedness (70 scans total). The FreeSurfer image analysis suite was used to quantify longitudinal changes in cortical thickness and surface area.

Accelerated cortical thinning for the ASD group as compared to the TD group was found in 2 areas in the left hemisphere, the posterior portion of ventral temporal cortex and superior parietal cortex (cluster corrected p < .01). For ventral temporal cortex, cortical thinning was associated with everyday executive function impairments, and thinner cortex at time 2 was correlated with ASD social symptoms. Differences in surface area changes were not detected.

The present longitudinal study extends prior cross-sectional research by demonstrating increased cortical thinning (in portions of temporal and parietal cortex) but comparable surface area growth rates in participants with ASD compared to TD controls during adolescence and into young adulthood. These findings provide further evidence for atypical cortical development beyond the early years in ASD, marked by increased cortical thinning in late adolescence/young adulthood.