A Research Of Functional Brain Network In Epilepsy Based On Global Signal Topography

Epilepsy is a common chronic brain disorder with network dysfunction,accompanied by a large-scale disruption of excitatory and inhibitory neural interactions.With the rapid development of various neuroimaging techniques,especially functional magnetic resonance imaging(fMRI),there have been many studies on the pathological mechanism of epilepsy.The overall activity of the whole brain can be measured by socalled global signal(GS)in fMRI.However,most resting fMRI studies have regressed GS to better isolate functional networks,and this regression may fundamentally ignore meaningful GS changes in disease.Recent evidence from resting-state fMRI studies shows that the global signal fluctuations that are often overlooked in previous studies are not only non-neuronal physiological noise,but also an important source of neuronal activity itself,associated with meaningful neurophysiological activity in the brain.However,there is little work on global signaling in idiopathic generalized epilepsy(IGE)and temporal lobe epilepsy(TLE),and the mechanisms underlying the global pattern of fMRI spontaneous fluctuations in epilepsy remain unclear.Therefore,it is of scientific significance to explore abnormal global signal patterns in different types of epilepsy.Here,we quantified GS topography using beta weights obtained from a multiple regression model in a large group of epilepsy with different subtypes(n = 98,n =116)and healthy population(n = 151).We revealed that the non-uniformly distributed GS topography across higher-order association and sensory-motor networks in healthy controls was significantly shifted in patients.In particular,GS contribution was decreased in sensory networks such as the visual cortex,middle temporal gyrus and subcortical structures of the midbrain tegmentum,and increased in higher-order networks such as the orbitofrontal and medial frontal cortex.Additionally,such shifts of GS topography disturbances were more widespread and bilaterally distributed in generalized epilepsy,whereas in focal temporal epilepsy,these networks are spread beyond the epileptic focus but remain lateralized.Importantly,we found that these abnormal GS topography patterns were likely to evolve over the course of a longer disease.The present study demonstrates that epileptic processes can potentially affect global excitation and inhibition balance and shift the normal information flow of the brain.On this basis,we studied the dynamic properties of the global signal in the idiopathic generalized epilepsy and temporal lobe epilepsy with the sliding window method.Higher dynamic global signal variability was found at cuneus and occipital lobe in both healthy control and patient group.Further,we found that patients with idiopathic generalized epilepsy had higher global signal variability in bilateral angular gyrus,precuneus,middle frontal gyrus and inferior frontal gyrus and the temporal lobe epilepsy patients had lower dynamic global signal variability in the hippocampus\parahippocampus,cerebellum and medial frontal cortex.Post-hoc analysis showed that the global signal stability of default network,frontal-parietal network,salience network,auditory network,sensory-motor network and limbic network were significantly changed.These progressive topographical GS disturbances in subcortical–cortical circuits may underlie pathophysiological mechanisms of global fluctuations in human epilepsy.