Brain activity dynamics after traumatic brain injury indicate increased state transition energy and preference of lower order states

Fig. 1. Recurrent brain states. (A) The centroids of each of the four brain states, representing the average brain activity for that state. Yellow indicates high amplitude activity and purple indicates low amplitude activity. a.u. = arbitrary units B) Radial plots display the cosine similarity of each cluster centroid to the 7 Yeo functional networks, plus subcortex and cerebellum. States are labeled at the top by the most similar functional network and the type of activation (high amplitude is denoted with + and low amplitude is denoted with −). VIS = visual; SOM = somatomotor; DAT = dorsal attention; VAT = ventral attention; LIM = limbic; FPN = frontoparietal; DMN = default mode (Yeo et al., 2011); SUB; subcortex. CB = cerebellum. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. Individuals with TBI show a delayed, persistent shift in brain state occupancy and dynamics, wherein they favored lower-order visual and disfavored higher-order default mode states compared to non-injured controls. (A) Fractional occupancy rates for each of the four states, for non-injured controls (hc) and individuals with TBI at each post-injury time point. (B) T-statistic of HC vs TBI groups’ state-pair transition probabilities at each post-injury time point. *uncorrected p < 0.05 **corrected p < 0.05.

Fig. 3. Individuals with mild TBI show a trend toward delayed increase in global transition energy (and a significant decrease in global entropy) in such a way that is correlated with mean reaction time. (A) Global transition energy for non-injured controls and individuals with mild TBI at each time point. (B) Global entropy for non-injured controls and individuals with TBI at each time point. (C) Spearman correlation between global transition energy and MRT for individuals with mild TBI at each timepoint. Points are colored by their collection time post-injury. p-value displayed is corrected. *uncorrected p < 0.05.

Fig. 4. Individuals with TBI have decreased bottom-up versus top-down transition energy asymmetry. (A) T-statistics of the group differences (HC vs. individuals with mild TBI) in transition energies between pairs of brain states at each time point. (B) Transition energy asymmetry (the average difference between bottom up transition energy minus top down transition energy) for each pair of states *uncorrected p < 0.05 **corrected p < 0.05.

Fig. 5. Independent, moderate to severe TBI dataset shows delayed global transition energy increase and correlation between energy and attention. (A) Global transition energy for HC and TBI patients at each time point. (B) Global entropy for HC and TBI patients at each time point. (C) Transition energy asymmetry by group given by the average difference between bottom up transition energy and top down transition energy for each set of pairwise transitions. (D) Spearman correlation between global transition energy and MRT for TBI patients at each timepoint. p-value displayed is corrected. (E) T-statistics of the group differences in transition energies between brain activity states in HC vs. TBI subjects at each time point *uncorrected p < 0.05 **corrected p < 0.05.