What lies underneath: Precise classification of brain states using time-dependent topological structure of dynamics
Fig 2
Measures of information structures.
An information structure (IS) is shown on the left. It is determined by the structural connectivity matrix (fixed) and the αi values (variable at each instant) for the 7 networks in Yeo’s parcellation. The nodes of the information structure correspond to stationary states of the system. Networks with a value greater than 0 are coloured. The IS can be studied through several measures. NoEL (number of energy levels) corresponds to the number of layers in the IS (levels 0 to 4). Frondosity is the ratio of nodes in the IS with respect to the maximum for its NoEL. Cooperation measures focus on cooperative nodes, which are those (except for level 1) where a network that does not appear on its own occurs in presence of other networks. The highest cooperation level is given by the highest level at which a cooperative node appears. Cooperation values consider cooperative nodes in different ways. Cooperation value A counts all cooperative nodes, adding in each case the level of the node from which it proceeds. Cooperation value B considers only one level (the lowest) for each new network, and cooperation value C operates in the same way but by adding powers of 2. Other used measures are criticality and synchronicity. Criticality measures how close is the globally stable node to a bifurcation point that modifies which are its active and inactive networks. Finally, synchronicity measures the ratio of IS of a subject (across time) in which all networks appear in the same state (active or inactive) in the globally stable solution.