Resting state brain connectivity via bicoherence and coherence

Kandemir, Ahmet Levent
The human brain is a complex and dynamical system, which consists of segregated areas specialized for perceptual or motor processing. Task-specific functions are only carried out by integration of these segregated regions. Thus, in order to understand the human brain, it is very important to understand underlying network structure. There are various metrics to investigate the brain connectivity and each day, new metrics are introduced in the field. This study concentrates on bicoherence analysis. Bicoherence is a third order spectral coupling measure which is used to investigate nonlinear interactions, particularly quadratic phase coupling, within the brain. High computational cost and being prone to volume conduction effect has made bicoherence impractical in neuroscience. New approaches to bicoherence promise reduction in computational cost and robustness to volume conduction. ‘Sliced Bicoherence’ is a bicoherence metric calculating only the main diagonal of the bicoherence matrix with a significant reduction in calculation time. Sufficiency of calculation of only the main diagonal of the matrix has been an open question about the subject. On the other hand, newly introduced ‘Subtracted Bicoherence’ is an improvement over ‘Sliced Bicoherence’, eliminating volume conduction. Within the scope of this study, it was shown that the information content of bicoherence matrix was concentrated on the main diagonal. Also, validity and usability of ‘Sliced Bicoherence’ and ‘Subtracted Bicoherence’ in connectivity analysis were demonstrated by comparing them to well known ‘Coherence’ and ‘Imaginary Coherency’ metrics.
Citation Formats
A. L. Kandemir, “Resting state brain connectivity via bicoherence and coherence,” M.S. - Master of Science, Middle East Technical University, 2018.