Figure 1:

The calculation of Intrinsic Network Reactivity Index (INRI) includes three main steps of (a) identifying intrinsic events, (b) obtaining brain state trajectories, and (c) quantifying the brain state trajectories. In (a), each channel is recursively selected as a trigger channel, and a typical response to three sigma events (+3σ) of this trigger channel in rest of the channels (target channels) is calculated. Next, the resulting response signals are averaged for each subject group (in this case different GCS values and control subjects). In (b), the typical response signals from the previous step are collapsed into three dimensions using principal component analysis. Finally, in (c), the three-dimensional data of the previous step is quantified by fitting a surface to the absolute value of obtained trajectories and calculating the directional derivative of the projection of trajectory points on the fitted surface in the direction of the final point in the time domain.