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
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