Spinal cord stimulation modulates complexity of neural activities in patients with disorders of consciousness

Objective: Spinal cord stimulation (SCS) is a valuable treatment for patients with disorders of consciousness (DOC). This study used permutation entropy (PeEn) of neural activities to quantify brain responses to SCS. Method: We recruited 14 patients with DOC, including seven patients in minimally conscious state (MCS) and seven patients in vegetative state/unawareness state (VS/UWS). All patients received a single session of 20 min' continuous SCS. We recorded resting state EEG before, during and after SCS. In this study, PeEn was first calculated to describe overall neural activities changes in SCS. The brain was then divided into frontal, central, parietal and occipital regions to explore spatial SCS modulation effects. Finally, a correlation analysis was conducted between CRS-R values and changes in PeEn on each of the four regions. Results: SCS was associated with short-term changes in neural activities in DOC. When SCS was on, PeEn increased as compared to the baseline. When SCS was shut off, PeEn decreased. The PeEn of all patients after SCS was higher than before SCS, and changes of PeEn for MCS were more significant than those for VS, especially in the frontal region. Conclusion: PeEn from EEG data could be used to evaluate SCS modulation effects, and EEG complexity might be a critical index to describe brain responses to SCS in DOC.