Mentalization Network Gray Matter Volumes Abnormalities in Autism Spectrum Disorders

Background: Autism Spectrum Disorders (ASD) share common deficits in social and communication skills. One influential cognitive theory proposed to explain these impairments is ‘mind-blindness’, i.e. deficiency in the ability to attribute states of mind (including emotions, desires and goals) to other people. This process, also known as Theory-of-Mind (ToM), or Mentalization, is a crucial component of social behavior allowing prediction and interpretation of others’ behavior. The brain network involved in this process includes the temporoparietal junction (TPJ), temporal pole (TP) and medial prefrontal cortex (MPFC). We previously demonstrated that ASD patients underactivate this network while engaged in a social, competitive game that entails on-line mentalization. In addition, previous studies showed that ASD patients exhibit abnormal gray matter (GM) volumes in widespread brain areas. In the current study, we examined GM abnormalities of ASD patients specifically in the mentalization network.

Objectives: To compare GM volumes of ASD patients to matched healthy controls (HC) in the mentalization network (i.e. TPJ, TP and MPFC), and to investigate the relationship between ASD GM volumes of this network and the severity of patients’ symptoms as measured by the ADOS.

Methods: Twenty-one high functioning ASD patients, ages 11-32, and 23 matched HC, ages 10-29, underwent an MRI scan. Structural MPRAGE T1-weighted images were acquired with a 3T scanner. Voxel-Based Morphometry (VBM) analysis was done using SPM2.

Results: Compared to HC, ASD patients showed increased GM volumes in the MPFC and bilateral TPJ, and decreased GM volumes in bilateral TP. Positive correlations were found between MPFC GM volume and patients’ ADOS scores.

Conclusions: High-functioning ASD patients showed abnormal GM volumes in the mentalization network, within MPFC volumes correlated with their symptom severity. These results support the theory that neuropathologic changes in specific brain regions underlie the mentalization impairments of ASD.