Transdiagnostic Neurobiology of Social Cognition and Individual Variability as Measured by Fractional Amplitude of Low-Frequency Fluctuation in Autism and Schizophrenia Spectrum Disorders.

Background: Fractional amplitude of low-frequency fluctuation (fALFF) is a validated measure of resting-state spontaneous brain activity. Previous fALFF findings in autism and schizophrenia spectrum disorders (SSDs) have been highly heterogeneous. We aimed to use fALFF in a large sample of typically developing control participants (TDCs), autistic participants, and participants with SSDs to explore group differences and relationships with interindividual variability of fALFF maps and social cognition.

Methods: fALFF from 495 participants (185 TDCs, 68 with autism, and 242 with SSDs) was computed using functional magnetic resonance imaging as signal power within 2 frequency bands (i.e., slow-4 and slow-5), normalized by the power in the remaining frequency spectrum. Permutation analysis of linear models was used to investigate the relationship of fALFF with diagnostic groups, higher-level social cognition, and lower-level social cognition. Each participant's average distance of fALFF map to all others was defined as a variability score, with higher scores indicating less typical maps.

Results: Lower fALFF in the visual and higher fALFF in the frontal regions were found in both participants with SSDs and autistic participants compared with TDCs. Limited differences were observed between autistic participants and participants with SSDs in the cuneus regions only. Associations between slow-4 fALFF and higher-level social cognitive scores across the whole sample were observed in the lateral occipitotemporal and temporoparietal junction. Individual variability within the autism and SSD groups was also significantly higher than within the TDC group.

Conclusions: Similar patterns of fALFF and individual variability in autism and SSDs suggest some common neurobiological features across these related heterogeneous conditions.