Functional Connectivity Analysis under Vigilance Decrement and Enhanced Mental States

A Master of Science thesis in Biomedical Engineering by Omnia Hassanin entitled, “Functional Connectivity Analysis Under Vigilance Decrement and Enhanced Mental States”, submitted in June 2020. Thesis advisors are Dr. Hasan Al Nashash, Dr. Usman Tariq and Dr. Fares Yahya. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).

Abstract

This thesis proposes electroencephalogram (EEG) functional connectivity and graph theory analysis (GTA) to quantify brain activity under alertness, vigilance decrement, and enhanced mental states in four frequency bands. The vigilance decrement state was induced by performing a 30 min computerized incongruent Stroop color-word test (ISCWT). Meanwhile, the enhancement states were provoked by integrating a 250Hz pure sinusoidal tone (PST) or 16Hz beta binaural beats (BB) with the I-SCWT. We estimated functional connectivity using the phase-locking value (PLV) statistic and characterized the topological structure of the network based on concepts of node strength, clustering coefficient, and efficiency. We then evaluated the proposed methods using statistical analysis and a support vector machine classifier. The experimental results showed that the 30 min I-SCWT significantly elicited alteration in cortical connectivity (p < 0.05). PLV between brain regions significantly decreased with vigilance decrement (p<0.05), resulting in a less optimal network structure. Investigation of the intra-regional PLV networks suggested that changes in connectivity under vigilance decrement are specific to cortical areas and EEG frequency bands. Our Assessment results confirm that PLV+GTA provides a reliable index to quantify different aspects of cortical functional connectivity under different vigilance levels. Subject independent classification analysis based on GTA features corresponding to a single cortical region showed an average accuracy of 84.27% to discriminate vigilance decrement from alertness state. Under enhanced mental states, cortical connectivity remained high until the end of the total task duration. Also, significant improvements in the participants’ performance were observed in comparison to the no-audio condition. On average, PST stimulation showed a 25.84% improvement in the participants’ detection accuracy towards the end of the task. Similarly, BB stimulation showed a 26.01% improvement.