Fig. 3: Estimating the arrow of time in brain signals provides significantly different signatures of brain state.

The figure summarises the results of analysing all the available (eyes closed) data from the non-human primates in sleep and four different states of anaesthesia (see Methods and Fig. 2). a The column shows individual examples of the functional connectivity matrices across the 128 electrodes and a scatter plot of the correlation between each condition. As can be seen, this conventional method is unable to distinguish between the very different brain states. b In contrast, the central panel shows the application of the thermodynamic framework of estimating the arrow of time on the same individual time series, which is clearly distinguishing brain states. c The column shows the significant group level results (across all non-human primates with all sessions belonging to the specific brain state) which provides a clear signature able to distinguish between different brain states (Wilcoxon rank-sum, p < 0.001).