Neural Signatures of Discrepant Nonverbal and Verbal IQ in Youth with ASD

Background: Research suggests that discrepant cognitive abilities (non-verbal IQ [NVIQ] > verbal IQ [VIQ], and VIQ > NVIQ) are more common in youth with ASD than in normative samples, and the NVIQ>VIQ pattern has been found to be associated with more severe autism symptomatology. However, the neural underpinnings of discrepant cognitive abilities in youth with ASD have not yet been established. Understanding the neural basis for IQ discrepancy is important because it may inform a critical ASD endophenotype and lead to greater understanding of the biology underlying heterogeneity in the presentation of ASD.

Objectives: We sought to investigate the neural basis of discrepant cognitive abilities in youth with ASD. We used a well-validated fMRI task engaging social perception and evaluated, on a whole-brain level, the neural correlates of the (NVIQ minus VIQ) difference score, while controlling for ASD symptom severity and full-scale IQ.

Methods: Sixty-seven children and adolescents (4-17 yrs., 54 males) with high-functioning ASD participated. They passively viewed alternating blocks of point-light displays of biological versus scrambled motions in a Siemens 3T scanner. All participants were diagnosed with ASD using the Autism Diagnostic Observation Schedule (ADOS), and the final diagnosis was confirmed by expert clinical judgment. Cognitive abilities were assessed with the Differential Abilities Scales-Second Edition (DAS-II).

Results: The NVIQ/VIQ discrepancy cutoffs were determined using DAS-II normative criteria of a significant discrepancy. Participant groupings (NVIQ>VIQ, NVIQ=VIQ, VIQ>NVIQ) did not differ significantly on age, gender, full-scale IQ, ASD symptom severity (as measured by ADOS CSS score) and head motion in the scanner. Our sample showed a greater trend of individuals with NVIQ>VIQ (21%) and VIQ>NVIQ (19%) when compared to the normative criteria (15%), but this difference is not significant, chisq(2) = 3.54, p = .17. For this reason, we did not test for group differences but treated the difference score, NVIQ minus VIQ, as a continuous variable. The (NVIQ minus VIQ) difference score was positively correlated with activation to biological versus scrambled motion in the postcentral gyrus, middle temporal gyrus, lateral occipital cortex, precuneus, inferior temporal gyrus, and fusiform gyrus, voxel-level Z > 2.326, cluster-level P < .05. Neurosynth-based functional decoding results indicate that these regions are primarily associated with visual perception, object recognition, spatial attention, and motion perception. Importantly, these neural correlates remained when controlling for ASD symptom severity and full-scale IQ score. Strikingly, ASD symptom severity was inversely correlated with the activation in the right posterior superior temporal sulcus (pSTS). 

Conclusions: Our results suggest that the magnitude of a participant’s NVIQ>VIQ discrepancy is associated with activity in a network of brain regions that are known to be engaged during early visual perception, object recognition, spatial attention, and general motion perception. Importantly, these neural correlates cannot be attributed to individual differences in ASD symptom severity or full-scale IQ level. Together, these results suggest that the NVIQ>VIQ discrepancy, as a feature underlying heterogeneity in the presentation of ASD, has its own neural basis that is separable from ASD core symptoms.