Abstract
Spinal cord stimulation (SCS) has become a valuable brain-intervention technique used to rehabilitate patients with disorders of consciousness (DOC). To explore how the SCS affects the cerebral cortex and what possible electrophysiological mechanism of SCS effects on the cortex, the present study investigated the functional connectivity and network properties during SCS in minimally conscious state (MCS) patients. MCS patients received both SCS and sham sessions. Functional connectivity of the phase lock value (PLV) in the gamma band (30–45 Hz) was investigated at the pre-, on- and post-SCS stages. In addition, to evaluate global network properties, complex network parameters, including average path length, cluster coefficient and small-world, were measured. When SCS was turned on, significantly decreased connectivity was noted in the local scale of the frontal-frontal region and in the large scales of the frontal-parietal and frontal-occipital regions. The global network showed fewer small-world properties, average path lengths increased and cluster coefficients decreased. When SCS was turned off, the large-scale connectivity and global network returned to its pre-SCS level, but the local scale of frontal-frontal connectivity remained significantly lower than its pre-SCS level. Sham sessions produced no significant changes in either functional connectivity or network. The findings directly showed that SCS could effectively intervene cortical gamma activity, and the intervention included immediate global effects (large scale connectivity and network alteration only occurred in stimulation period) and long-lasting local effects (local scale connectivity alteration persist beyond stimulation period). Moreover, considering the mechanism and propagation of gamma activity, it indicates that the frontal cortex plays a crucial role in the SCS effects on the cerebral cortex.
Highlights
IntroductionThere is currently no effective standardized treatment for patients with disorders of consciousness (DOC)
Despite considerable research, there is currently no effective standardized treatment for patients with disorders of consciousness (DOC)
We reported that Spinal cord stimulation (SCS) modulated frontal delta and gamma activity in patients in a minimally conscious state (MCS) (Bai et al, 2017), showing that SCS modulated the brain functions of MCS patients and providing EEG evidence supporting the potential mechanism for doing so: stimulating the reticular formation and further affecting the frontal cortical region through the formation-thalamus-cortex network
Summary
There is currently no effective standardized treatment for patients with disorders of consciousness (DOC). Studies have shown its efficacy in modulating the brains of DOC patients (Yamamoto et al, 2012, 2013, 2017), but the underlying mechanism of its effects on the cerebral cortex is still unclear. We reported that SCS modulated frontal delta and gamma activity in patients in a minimally conscious state (MCS) (Bai et al, 2017), showing that SCS modulated the brain functions of MCS patients and providing EEG evidence supporting the potential mechanism for doing so: stimulating the reticular formation and further affecting the frontal cortical region through the formation-thalamus-cortex network. Further research is needed to provide detailed evidence about the pathway by which SCS affects the cerebral cortices of DOC patients
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