Brain function evaluation in the minimally conscious state using cross-sample entropy based on brain network measure under the spinal cord stimulation

Abstract

Although spinal cord stimulation (SCS), as an effective method for consciousness modulation, has been applied in MCS, the underlying mechanism is still not clear. In this study, the resting-state EEG signals recorded from healthy volunteers were employed as a control group for comparison. The sample entropy, as well as the brain networks characteristics derived from the cross-sample entropy, were used to investigate the neural responses between the states of the pre-SCS and post-SCS. The results showed that the complexity of EEG signals increased in the frontal and central regions after the SCS. The SCS also enhanced the coupling mode in intra-region of pairwise channels within the frontal region and central region, as well as the inter-region channels between the frontal region with other regions in high frequency bands ($\\alpha$ 8$\\sim$13 Hz, $\\beta$ 13$\\sim$30 Hz, $\\gamma$ 30$\\sim$45 Hz). This indicated that the information integration increased after SCS. Also, compared with the pre-SCS state, the average clustering coefficient increased and the average path length decreased in the post-SCS state in high frequency band (from $\\alpha$ to $\\gamma$). Also, the small-world network characteristics of the patients in the high frequency band are significantly enhanced after SCS ($p<0.001$ in $\\alpha,~\\beta,$ and $\\gamma$). Compared with the healthy control group, the change directions of these indices tend to the brain function indices of resting states in normal subjects. There was no significant difference between pre-SCS in MCS patient state and the resting state in healthy control subjects in the sample entropy and cross sample entropy of some regions, such as the sample entropy of the $\\beta$ and $\\gamma$ frequency bands in the frontal and the central regions($p>0.05$). However, the parameters of brain networks still exist significant differences between the post-SCS and resting state. Therefore, we think that these indices changes after SCS may be induced from the “short-range effect of SCS. We speculate that the SCS has the ability to remodeling brain function through the “short-range effect. This study provided a new interpretation of the underlying mechanism of the SCS, and also provided a new perspective for assessing the brain function of the patients with MCS.