In recent decades, great progress has been made in the world in the development of methods for assessing directional interactions between objects of different nature from their experimentally measured signals. Moreover, more than two-thirds of all studies are devoted to the study of the connectivity between brain structures in normal and pathological conditions. The most common approach is Granger causality in its various variations. The book gives an overview of the current state of science in this area and provides original results of authors published in more than 30 different articles in leading scientific journals over the past 7 years. For scientists - physicists, mathematicians and biologists, university professors, graduate students.