Inter-hemispherical Investigations on the Functional Connectivity of Autistic Resting State fMRI

Inter-hemispherical Investigations on the Functional Connectivity of Autistic Resting State fMRI

Vidhusha S (Department of Information Technology, Centre for Healthcare Technologies, SSN College of Engineering, India) and Kavitha Anandan (Department of Biomedical Engineering, Centre for Healthcare Technologies, SSN College of Engineering, India)
DOI: 10.4018/IJCINI.2016040105
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Abstract

Autism spectrum disorders are connected with disturbances of neural connectivity. Functional connectivity is typically examined during a cognitive task, but also exists in the absence of a task i.e., “rest.” Adults with ASD have been found to show weaker connectivity relative to controls. This work focuses on analyzing the brain activation for autistic subjects, measured by fMRI during rest, relative to the control group using interhemispherical analysis. Though both groups activated similarly in cortical areas, indications of under connectivity were exhibited by the autistic group measured by Granger Causality and Conditional Granger Causality. Results show that as connectivity decreases, GC and CGC values also get decreased. The left hemisphere exhibits depreciation in the connectivity in comparison to that of right hemisphere for the autistic individuals whose GC and CGC values keeps decreasing in the left hemisphere seed regions. Finally, the results provide an approach for analyzing the cortical underconnectivity, in clinical relevance for diagnosing autism in children.
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Introduction

Autism is a brain disorder that involves multiple functional networks. While a growing number of studies indicate a general underconnectivity in autism patients, multiple studies contradict stating overconnectivity (Assaf et al, 2010). There is a suggestion of strong connections in sub regions of the autistic brain with a deficiency in long range connectivity (Bandettini, 1993). Such differences have been explained by a combination of factors such as task-regression, field of view and low pass filtering (Deshpande et al, 2013).

Task based studies dominated functional neuroimaging till functional scans of resting subjects were acquired and the correlation of a seed defined in the frontal-parietal cortex with respect to the rest of the brain was computed. This revealed that even in the absence of a task, regions performing similar functions or regions that would be modulated by a task exhibit functional connectivity (Ding et al, 2006). Since the publication of this study, numerous studies have replicated the experiment and confirmed the results. This has sparked an interest in analyzing resting state fMRI (rs-fMRI).

rs-fMRI studies have also confirmed the existence of a default mode network, that is particularly active during resting periods and whose activity diminishes while performing a task. This network has been found to include the posterior cingulate cortex (PCC), ventral medial prefrontal cortex (vMPFC), inferior parietal lobule (IPL), lateral temporal cortex (LTC), dorsal medial prefrontal cortex (dMPFC), and parahippocampal gyrus (PHC) (Dodel et al, 2005). Of these, posterior cingulate cortex, medial and lateral parietal cortex and medial prefrontal cortex were chosen as the task negative regions (i.e. regions whose activity is lowered during the performance of an attention-demanding task) while from other fMRI studies (Friston et al., 1993), a set of task positive regions- intra parietal sulcus (IPS), frontal eye field (FEF) and middle temporal region (MT) were identified (Subbaraj, P. K et al, 2014) and from the connectivity based correlation and conjunction analyses (Goebel et al, 2003) these task positive and negative regions were found to be anti-correlated. The study focused on comparative analysis between control and autistic subjects in task positive and task negative regions.

Functional connectivity provides a measure of temporal correlations between secluded physiological events (Kana et al, 2006). It is different from effective connectivity which depends on an apriori model for the cases of causal mode of relationship. Functional connectivity using fMRI (Chengaiyan, S., & Anandhan, K., 2015) was studied on the regions of motor cortex of resting state human brain using the relevance of product moment correlation of BOLD time courses. Functional connectivity measures can be tested for its implication and the reliability of functional connectivity among the nodes infers the way in which the integration of nodes (Van Den Heuvel et al, 2010) is allied in the functional network.

The objective of this work is to examine the resting state functional connectivity (rs-FC) in task positive and task negative regions in adults with ASD. The role of rs-FCs in the following regions: Task positive - Intra Parietal Sulcus(IPS), Frontal Eye Field(FEF), Middle Temporal region(MT), Task negative - Posterior Cingulate Cortex/Precuneus(PCC), Medial Prefrontal Cortex(MPF) and Lateral Parietal Cortex(LP) in 9 adults with high functioning ASD compared to 9 matched healthy controls of short R-fMRI scans were acquired from from the ABIDE database. The correlation results showed connectivity in both the groups. But, there were evident indications of under connectivity in the left hemisphere exhibited by the autistic group which was validated by computing the Granger Causality (GC) and Conditional Granger Causality (CGC) respectively.

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