Stationary stable cross-correlation pattern and task specific deviations in unresponsive wakefulness syndrome as well as clinically healthy subjects.

Brain dynamics is highly non-stationary, permanently subject to ever-changing external conditions and continuously monitoring and adjusting internal control mechanisms. Finding stationary structures in this system, as has been done recently, is therefore of great importance for understanding fundamental dynamic trade relationships. Here we analyse electroencephalographic recordings (EEG) of 13 subjects with unresponsive wakefulness syndrome (UWS) during rest and while being influenced by different acoustic stimuli. We compare the results with a control group under the same experimental conditions and with clinically healthy subjects during overnight sleep. The main objective of this study is to investigate whether a stationary correlation pattern is also present in the UWS group, and if so, to what extent this structure resembles the one found in healthy subjects. Furthermore, we extract transient dynamical features via specific deviations from the stationary interrelation pattern. We find that (i) the UWS group is more heterogeneous than the two groups of healthy subjects, (ii) also the EEGs of the UWS group contain a stationary cross-correlation pattern, although it is less pronounced and shows less similarity to that found for healthy subjects and (iii) deviations from the stationary pattern are notably larger for the UWS than for the two groups of healthy subjects. The results suggest that the nervous system of subjects with UWS receive external stimuli but show an overreaching reaction to them, which may disturb opportune information processing

Fig 5 -

(a) Stationary correlation pattern of subject 1 of the control group. Electrodes are ordered in such a way that the upper left and lower right square of each matrix display intra-hemispheric cross-correlations of the left and right hemisphere respectively. The lower left and upper right square show inter-hemispheric correlations. The three-by-three central square contains the correlation coefficients between the central electrodes and the rectangles display the correlations between hemispheric and central contacts. The diagonal elements of each matrix are set to zero to improve visual impression. (b) Stationary correlation pattern of each subject considered in the present study. First row, control subjects, middle row UWS, bottom row sleep.</p

10-second EEG segments of 5 electrodes.

A) one representative UWS patient; B) one subject of the control group during rest; C) one healthy subject during deep sleep and D) during REM sleep (see [31] for the description of the sleep subjects). The electrodes were selected to provide a representative image of the scalp.</p

First three moments of the cumulative probability distributions shown in Fig 9.

First three moments of the cumulative probability distributions shown in Fig 9.</p

P-values according to the Kolmogorov-Smirnov (KS) test for the comparison of the three experimental conditions (rest, rhythmic, arhythmic) for the control and UWS groups.

P-values according to the Kolmogorov-Smirnov (KS) test for the comparison of the three experimental conditions (rest, rhythmic, arhythmic) for the control and UWS groups.</p

First three moments of the cumulative probability distributions shown in Fig 7a.

First three moments of the cumulative probability distributions shown in Fig 7a.</p