Date of Award

10-4-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Computer Science

First Advisor

Kamran Iqbal

Abstract

Understanding physiological processes in the brain requires formal system models. Furthermore, connectivity is a core component of such models. According to recent studies, 70% of all information within the cortical regions in the brain passed through only 20\% of information processing nodes, commonly referred as "Connector Hub Nodes" (CHNs). Knowledge of these CHNs not only help to understand the information processing behavior of the cortex but also reveals the impact of neurogenerative diseases that affect the functional brain connectivity. CHNs have been previously identified using functional magnetic resonance imaging (f-MRI) method, however, we believe that Electroencephalography (EEG), despite its low spatial resolution, can provide a better perspective on cognitive dynamics. This study, therefore, aims at discovering the Antipodal Connectivity Structures (ACS) in the brain using EEG data. It further introduces two potential cognitive biomarkers, the Antipodal Hub Nodes (AHNs) and the Antipodal Entropy (AE). In this regard, this study tries to answer the following questions: What are the factors affecting the occurrence frequencies of AHNs? Is AHN occurrence related to the cognitive task at hand? If so, is there a direct correlation between the occurrence rate and distinct cognitive functions? Furthermore, what are the differences between healthy and cognitively disabled brain, in terms of AE? As per our experimental results, occurrence of AHNs was observed earlier in the younger group than the older group using visual stimulus. A positive correlation between the number of AHNs and their amplitude was discovered at earlier components (P1 and N1) in auditory and visual stimuli. Furthermore, Katz Fractal Dimension provided the highest accuracy (93.1 %) for classification of Obsessive Compulsive Disorder (OCD) versus the Antipodal Entropy (78.3 %). The AHN analysis also revealed that using network resources in the brain changed with age. Later AHN connectivity (160 ms) and increased activity on prefrontal regions in older subjects showed that such compensatory mechanism for low-level tasks could be a useful strategy to achieve similar success as younger subjects. This study also suggests that OCD not only affects the frontal lobe, but also can involve the parietal lobe (Higuchi Dimension) and the occipital lobe (Katz Fractal Dimension).

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