Entropy Metrics Correlating with Higher Residual Functioning in Patients with Chronic Disorders of Consciousness

Abstract

To test the ability of different entropy measures to classify patients with different conditions of chronic disorder of consciousness, we applied the Lempel-Ziv complexity, the amplitude coalition entropy (ACE), and the synchrony coalition entropy (SCE) to the EEG signals recorded in 32 patients, clinically evaluated using the coma recovery scale revised (CRS-R). All the entropy measures indicated that differences found in the theta and alpha bands can distinguish patients in a minimal consciousness state (MCS) with respect to those in a vegetative state/unresponsive wakefulness state (VS/UWS). These differences were significant comparing the entropy measure performed on the anterior region of the left hemisphere and midline region. The values of theta-alpha entropy positively correlated with those of the CRS-R scores. Among the entropy measures, ACE most often highlighted significant differences. The higher values found in MCS were for the less impaired patients, according to their CRS-R, suggest that the preservation of signal entropy on the anterior region of the dominant hemisphere correlates with better preservation of consciousness, even in chronic conditions.

Keywords: EEG; disorders of consciousness; entropy.

Figure 1

ACE values on left (L) (A); and right (R) (B) hemispheres. Significant differences between MCS and VS/UWS were observed on the left hemisphere only and are marked with asterisks. In each diamond box, the line represents the mean value, the diamond height represents the SD and the whiskers represent the 10–90% range of the values. Panels C and D show, with the same colors as in A and B, the linear relationships between ACE measures and CRS-R score, which were significant on the left hemisphere only (the lines are shown only for significant relationships, with the same color of the symbols). The theta values are in light blue (circles in (C,D)), the alpha values in orange (triangles in (C,D)), and the beta values are in dark green (diamonds in (C,D)).

Figure 2

ACE values on left (L) and right (R) fronto-central (A); and midline (D) regions. Panels (C) shows the ratio between measures on left and right fronto-central regions; Panel (B) shows the linear relationships between ACE values obtained on the left fronto-central region and CRS-R values; Panel (E) shows the linear relationship between ACE values on the midline region and CRS-R values. Values and lines that did not give significant relationships are not shown. Colors and symbols as in Figure 1. Significant differences are marked with asterisks.