Functional Dysconnectivity in Autism Spectrum Disorder Revealed by Network-Based Statistics.
AmirHussein Abdolalizadeh1, Bahram Mohajer1, and Nooshin Abbasi1

1Students Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran

Synopsis

Since the advent of Connectomics, borders of our knowledge about brain and nervous system have increased tremendously. Thus, novel methods to analyze brain connectivity have always been under focus. We used Network-based statistics (NBS), to exert a weak control over family-wise error, and discover interconnected networks in 35 Autism Spectrum Disorder (ASD) and 34 age-, sex- matched Typically developing (TD) children. We also used NBS results' nodes for structural connectivity analysis. We respectively showed increased and decreased functional connectivity of fronto-inferior temporal and default-mode networks, in patients with ASD compared to TD.

Introducion

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder known by aberrant functional and structural brain connectivities. The main outcome of this “dysconnectivity” is usually a triad of repetitive behaviors, underdeveloped social skills, and delayed or no language development.[1] Underlying causes of ASD are still poorly understood and there have been efforts to identify the brain pathology in this disorder[2]. One of the promising approaches is the use of connectivity matrices generated by functional or structural brain MRIs to explore graph metrics. Despite their usability, these approaches are subject to several problems including family wise error (FWE) in multiple comparisons[3]. One of the provided solutions is Network-based statistics (NBS)[4], which is a permutation based thresholding of graph matrices and applies a weak control over FWE. Moreover, functional and structural connectivity relationship is one of the recent interests in brain imaging studies[5]. In this study, we used NBS to identify functionally connected nodes, then we compared structural graph metrics in these nodes to see function/structure relationship in ASD.

Methods

We used an online open-source connectivity database (umcd.humanconnectomeproject.org)[6]. “UCLA_Autism” study connectivity matrices were used[7]. This study contains both structural and functional connectivity matrices for 69 subjects (35 ASD, 34 Typically Developing “TD”). The atlas used was generated by Power et, al. This atlas is very sensitive and specific to functional MRI connectivity signals and can be a better predictor of true functional connectivity[8]. These data are matched for age, sex and IQ. Structural matrices were number of fibers between two regions. The weighted structural matrices were built, as a number of fibers connecting two labels divided to all fibers in that network[9]. We used z-transformed functional matrices in NBS with 10000 permutations and t-threshold of 3.4 for two contrasts: ASD>TD and TD>ASD. The resultant significant nodes of functional matrices were then fed into Brain Connectivity Toolbox (BCT)[10] to calculate Local Efficiency (which is a measure of network segregation) from structural matrices. The results were analyzed with R v3.2.2 (https://www.r-project.org/) and corrected for false discovery rate (FDR).

Results

NBS showed a network of significant increased functional connectivity in ASD compared to TD (fig. 1, p-value=0.033). This network is comprised of 23 nodes and edges mostly connecting frontal and posteroinferior temporal cortices. On the other hand, in TD, NBS revealed a subnetwork of increased functional connectivity comprised of edges mostly connecting default-mode network (DMN) of the brain (e.g. precuneus, cingulate gyrus, angular gyrus; fig. 2, p-value=0.030). Our post-hoc analysis revealed no significant differences in local efficiency in the selected nodes.

Discussion

ASD is a neurodevelopmental disorder characterized by behavioral and cognitive problems[1]. Despite medical advances, the pathophysiology of this disease is still poorly understood. In this study we used NBS to investigate functional connectivity in ASD comparing to TD. Our study showed functional dysconnectivity in ASD. We found that frontal and posteroinferior temporal cortices’ show abnormally left-sided increased functional connectivity. This network is largely associated with social cognition and increased connectivity in this network may somehow explain the social problems in ASD, although studies relating social impairment and this network are required[11]. Moreover, patients with ASD showed reduced connectivity in DMN. DMN is anti-correlated with task-related networks and is believed to be involved in task-independent self-introspection[12]. Our finding is consistent with many studies indicating decreased functional connectivity in DMN, which has been related to symptoms of ASD[13]. We offer a new approach to study brain functional and structural connectivity. One of the solutions for family-wise errors is using the candidate nodes, i.e. choose limited number of nodes based on a hypothesis[3]. We propose a systematic approach, using NBS to identify significantly differing functionally nodes and investigate structural graph metrics in those to have brain function and structure in one view, although we didn’t find significant results. In conclusion, NBS reveals abnormally increased and decreased connectivity in frontotemporal network and DMN, respectively, which may be contribute to ASD’s clinical presentations.

Acknowledgements

No acknowledgement found.

References

1. Conti, E., et al., The first 1000 days of the autistic brain: a systematic review of diffusion imaging studies. Frontiers in Human Neuroscience, 2015. 9. 2. Rojas, D.C., et al., Hippocampus and amygdala volumes in parents of children with autistic disorder. American Journal of Psychiatry, 2015. 3. Fornito, A., A. Zalesky, and M. Breakspear, Graph analysis of the human connectome: Promise, progress, and pitfalls. NeuroImage, 2013. 80: p. 426444. 4. Andrew, Z., F. Alex, and T.B. Edward, Network-based statistic: Identifying differences in brain networks. NeuroImage, 2010. 53(4). 5. Sui, J., et al., Function–structure associations of the brain: evidence from multimodal connectivity and covariance studies. Neuroimage, 2014. 102: p. 11-23. 6. Brown, J.A. and J.D. Van Horn, Connected brains and minds—The UMCD repository for brain connectivity matrices. NeuroImage, 2015. 7. Rudie, J.D., et al., Altered functional and structural brain network organization in autism. NeuroImage: Clinical, 2012. 2. 8. Power, J.D., et al., Functional network organization of the human brain. Neuron, 2011. 72(4): p. 665-678. 9. Nir, T.M., et al., Connectivity network measures predict volumetric atrophy in mild cognitive impairment. Neurobiology of aging, 2015. 36: p. S113-S120. 10. Mikail, R. and S. Olaf, Complex network measures of brain connectivity: Uses and interpretations. NeuroImage, 2009. 52(3). 11. Kana, R.K., et al., Altered Medial Frontal and Superior Temporal Response to Implicit Processing of Emotions in Autism. Autism Research, 2015. 12. Fernández-Espejo, D., et al., A role for the default mode network in the bases of disorders of consciousness. Annals of neurology, 2012. 72(3): p. 335-343. 13. Redcay, E., et al., Intrinsic functional network organization in high-functioning adolescents with autism spectrum disorder. Frontiers in human neuroscience, 2013. 7.

Figures

NBSview window for ASD>TD contrast. Note the increased functional connections between frontal and inferior temporal cortices.

NBSview window for TD>ASD contrast. Note the increased functional connections between medial frontal, association and cingulate cortex, comprising DMN.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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