EEG Global Signal And Its Application In Sleep

The global signal of the resting-state functional magnetic resonance(fMRI)constitutes an intrinsic fluctuation and presents an opportunity on characterizing and understanding the whole brain activity.Recently evidence is growing that GS contains physiologic information,but rarely reveals its related signal in electroencephalography(EEG).If there is EEG global signal,it will provide a new tool and perspective to understand brain function,just like fMRI global signal.This study defined a new EEG signal firstly,namely EEG global signal.It is calculated through Reference standardization technique of electroencephalogram(REST),and it can reflect the average electrophysiological activity of the whole brain.In this study,we conducted two experiments to explore EEG global signal and its application in sleep preliminarily.In the first study,the resting-state data of 24 healthy college students were collected using simultaneous EEG-fMRI technology,and then the EEG and fMRI global signals of each subject were calculated to explore the correlation between the two.We found fMRI global signal fluctuation showed a positive correlation with the power of EEG global signal in the ? band(30-45 Hz)and a negative correlation in the low frequency band(4-20 Hz).The results provided new evidence for the neurophysiologic information of fMRI global signal.In the second study,we collected the napping sleep EEG data of about 100 minutes from 14 healthy college students,and then explored the difference of spectrum and electrophysiological events of EEG global signal in different sleep phases.Since EEG global signal is an indicator of whole brain activity,we speculated that it would have unique advantages in characterizing the global alertness.We calculated the EEG power spectra in Wake,N1,N2,N3 stage respectively.Since the spindles is closely related to memory consolidation and is an effective indicators to characterize individual differences,then we analyzed sleep spindles in EEG global signal.It was found that the lower frequency(? and ?)power of the EEG global signal increased as the sleep depth increased,and were significantly different in different stage.There was no significant difference in the number of spindles in EEG global signal between men and women.In addition,we also found that,quantitatively,the sleep spindles were mainly local spindles.However,we still found the presence of global spindles.Its spatiotemporal pattern contains both local and global properties.The existence of global pattern of spindles was verified from the perspective of scalp EEG.The temporal lobes near earlobe,the parietal and frontal lobes near the central sulcus were the areas most likely to form global patterns of spindles.Inspired by fMRI global signal,this study defined a new signal as the EEG global signal.It can represent the average electrophysiological activity of the whole brain from the perspective of scalp.By exploring the relationship between EEG global signal and fMRI global signal,we found that they are closely related to each other.In view of the same neural source of the two,EEG global signal was the electrophysiological characteristic of fMRI global signal.More importantly,given the relationship between the two,EEG global signal might serve as a new biomarker for neuropsychiatric and other brain illnesses.We explored the EEG global signal at different sleep phases,and found that it basically retained slow-wave activity and spindle activity.It is different from the information obtained by a single electrode.Only when the spindles have reached a certain size,it can be shown as spindle discharge on EEG global signal.Because the spindles are involved in memory consolidation,spindle classification based on EEG global signal is expected to play an important role in basic research on memory consolidation during sleep.