Sleep Posture Influence Brain Network

People's daily life and night rest are always accompanied by posture changes,such as sitting and standing in daily work and study,and sleeping on one's side and back at night.Proper posture not only makes people comfortable,but also impact on individual cognitive,physical,and sleep.Several studies have shown that posture can influence perception and cognition,which in psychology is called “embodied cognition” that emphasizes the complex relationship among the cognitive ability,ongoing sense state,and surrounding environment.At the physiological level,posture can affect the various indicators of heart and head blood-vessel,these indicators also are closely related to the blood oxygenation level-dependent(BOLD)signal.Although in the neuroimaging field posture is paid little attention,there have been some electroencephalography(EEG)evidence implied posture impact on waking resting-state brain activity.Therefore,we should consider the impaction of environmental change on the brain and construct “embodied brain” model,in order to better understanding the ongoing interaction among the brain,body,and environment.Nowadays,EEG and functional magnetic resonance imaging(fMRI)are the most frequently neuroimaging techniques used in studies.In fMRI experiments,participants are always required to lie supine,while EEG experiments usually require participants to sit upright.From the point of design view,fMRI is suitable for the supine position,and this posture is mostly used in sleep.Even during sleep,most people using lateral position,especially right-lateral position,and the second used position is the supine position.Thus,it seems fMRI is particularly suitable for the sleep study.There are few studies demonstrated that posture can influence the waking resting-state EEG,but lacking direct evidence of posture impact on fMRI BOLD signal.However,we can speculate from some aspects,firstly,the posture can influence the index of heart and head blood-vessel,these indicators are closely related to the fMRI BOLD signal.Secondly,posture can affect the functional near-infrared spectroscopy(fNIRS)signal,which is extremely similar to the fMRI signal.Thus,posture is likely to impact on fMRI data.But now there is no empirical studies have shown that posture impact on fMRI data.This is mainly due to the limited equipment,fMRI cannot scan the upright posture,therefore,it is difficult to verify the posture on vertical angle change affect the neural signal.So,the present study selected the right-lateral position and the supine position allowed by the fMRI environment to study and compared the brain activity change of resting state and slow wave sleep state in two postures.In study 1,using simultaneous EEG-fMRI technology separately recorded the 5 minutes waking resting-state in the supine position and right-lateral position.Of waking resting-state fMRI data after using ICA decomposed components and extracted the ALFF and functional connectivity to analyze,and then analyzed the correlation relationship between the two indicators and questionnaires(PSIQ and sleeping posture questionnaire),finally has carried on the analysis of heart rate and heart rate variability index.Of waking resting-state,fMRI data analysis found that under the condition of open eyes,default-mode network(DMN),sensorimotor network(SMN),and dorsal attention network(DAN)have shown higher ALFF in supine position compared the right-lateral position,however,only two components of the sensorimotor network(SMN-m,SMN-b)shown a significant statistical difference in two postures after Bonferroni correction.Functional connectivity among DMN,SMN,and DAN have been changed by posture.These functional connectivities are higher in the supine position compared with right-later position,however,only the functional connectivity between DMNmPFC and SMN-b and functional connectivity between DMN-ang and DAN is statistically significantly difference after Bonferroni correction.Further correlation analysis found that the different value of ALFF between two postures is not significantly correlated to the questionnaire score,while the difference value of functional connectivity between two postures is significantly correlated to the questionnaire score.Specifically,the difference value of functional connectivity between DMNmPFC and SMN-b is negatively related to supine position score and is positively related to the rightlateral position score.The different value of functional connectivity between SMN-b and SMN-m is positively related to the PSQI scores.In ECG analysis,heart rate has shown higher in right-lateral position compared with supine position,although did not reach a significant level,this trend is consistent with previous studies.For heart rate variability,LFP,HFP,TP,and nLF is higher in rightlateral position compared with supine position.In study 2,using simultaneous EEG-fMRI technology separately recorded the 50 minutes sleep data in the supine position and right-lateral position.Firstly,after removing the artifact in the EEG data,we extracted the slow-wave sleep fMRI data according to the EEG characteristics.Of slow-wave sleep fMRI data after using ICA decomposed components and extracted the ALFF and functional connectivity to analyze,and then analyzed the correlation relationship between the two indicators and questionnaires(PSIQ and sleeping posture questionnaire).fMRI indicators analysis found that during slow-wave sleep cerebellum shown significantly higher ALFF in the supine position compared with the right-lateral position;while DMN has shown and sensorimotor network shown higher ALFF but not significant.Correlation analysis found that ALFF and the differential value of functional connectivity under two posture conditions showed a significant correlation with questionnaire score.During slow-wave sleep,the difference value of ALFF cerebellum network under two posture conditions shown a significant negative correlation with PSQI scores;right-lateral position scores shown a significant positive correlation with the difference value of functional connectivity between SMN1 and cerebellum and significant negative correlation with the difference value of functional connectivity between SMN2 and DMN2.In a word,we can draw the following conclusions: first,posture can change the BOLD signal during awake and slow wave sleep: whether during awake resting state or during slow wave sleep,brain activity in supine position level is higher than right-lateral position.Secondly,the influence of the position of brain activity may be dependent on the conscious state: during awake resting state,posture obviously affects sensorimotor network;during slow wave sleep,posture obviously affects cerebellar network.Thirdly,the influence of posture on brain activity associated with daily sleeping position preference.Our research is exploratory,we show the effect of posture on brain activity,and explored the relationship between brain activity and daily sleeping position preference,the present study provides a reference for the neural mechanism of posture impact on brain activity.