11:00 : Hernando Ombao (C.035)
14:30 : Philippe Naveau (C.115)

11:00 : Hernando Ombao (C.035)

King Abdullah University of Science and Technology (KAUST) - Saudi Arabia
Invited by Rainer von Sachs

Connectivity in a Brain Network: An Overview

Abstract:

The brain can be considered as a system consisting of nodes at different levels starting from the microscopic to macroscopic: neurons, local fields, anatomical voxels, channels, regions of interest. One of the key problems in studying brain function is connectivity which reflects how different nodes of the brain interact with each other during rest and during a cognitive task. The first part of the talk will cover background material on the measures of functional connectivity which covers both time domain (cross-correlation) and frequency domain (coherence, partial coherence). Here, we also present our proposed metric, which we call spectral transfer entropy (STE) which quantifies the magnitude and direction of information flow from a certain frequency-band oscillation of a channel to an oscillation of another channel. Our approach utilizes the vine copula representation under which it is straightforward to test for the null hypothesis (zero STC) through a standard resampling approach.
In the second part of the talk, we consider the problem of characterizing "global” dependence between two regions, each consisting of many nodes. The naïve approach of computing all pairwise dependence is computationally demanding. Our approach is inspired by canonical coherence analysis (CCA) and in essence examines summarized dependence between the oscillatory activity at the pair of regions.  To overcome the limitations of CCA (linearity and sensitivity to outliers), we use the Kendall’s tau as a measure of dependence between the summarized oscillatory activity.
These proposed spectral dependence measures will be used to examine human electeoencephalograms (EEGs) and calcium recordings in mice.
This talk is based on joint work with Paolo Redondo, Mara Talento, and Sarbojit Roy.

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