Network Sculpting Index Suggests Impaired Functional Network Differentiation in ASD
Objectives: To evaluate the efficiency of neurotypical networks (DMN, MNS, ToM) in ASD and typically developing (TD) groups by calculating a network sculpting index (NSI), a ratio of within network connectivity and outside network connectivity.
Methods: Resting-state functional MRI data were acquired for 6:10 minutes for 33 children and adolescents with ASD (7-18 y/o) and 33 TD participants matched for age, motion, and non-verbal IQ. Standard preprocessing involved motion and field map correction, spatial smoothing, low bandpass filtering (.008<f<.08Hz), nuisance regression, and standardization to MNI152 template. For each network (DMN, MNS, ToM), regions of interest (ROIs) were identified using 6mm-radius spheres centered on previously reported coordinates (Van Overwalle & Baetens, 2009; Watanabe et al., 2012). Within-network masks were created for each ROI, including the seed and all other ROIs in the network (dilated to 12mm radius); outside-network masks excluded all network ROIs and non-cortical voxels. Individual whole-brain correlation maps (using average time series extracted from seed) were cluster corrected (p<1-6) and Fisher-transformed to z’. For each network, the number of significant voxels, weighted by z’, was determined for within- and outside-network masks, and was then used to calculate the NSI using the formula: NSI = (WNC-ONC)/(WNC+ONC), with WNC and ONC being within and outside-of network connectivity, respectively.
Results: Mean NSI was significantly reduced in the ASD group (p<.05) for DMN whereas no significant differences were detected for MNS or ToM. A correlational analysis of NSI and three a priori selected social measures (ADI-Social, ADI-Communication, and ADOS Communication + Social [CS] scores available for ASD participants only) revealed a negative relationship between NSI and ADOS CS in MNS (r=-0.35, p<.05) and ADI-Communication scores in ToM (r=-.39, p<.05). Based on these correlations, a post hoc analysis was performed in a subset of ASD participants (n=25) with highest level of social symptomatology as defined by ADOS CS scores ≥10. Direct group comparison of this ASD subsample and 25 TD participants matched on age, motion, and non-verbal IQ corroborated earlier results in DMN (TD>ASD, p<.05). In addition, this analysis yielded significant between-group differences in mean NSI for MNS and ToM (TD>ASD, p<.05).
Conclusions: Findings suggest that DMN is less efficiently sculpted in individuals with ASD, compared to TD controls (more connectivity outside of the network than within). Concordant between-group differences were also found for MNS and ToM networks, but these were detected only in ASD participants with relatively high symptom severity.