Electrophysiological Studies On Rat Default Mode Network

The resting brain is not “idle” but shows spontaneous,organized,and continuous neuronal activities,and contains various resting-state networks(RSNs).The default mode network(DMN)– one of the RSNs – has been attracting increasing research attention because of its unique metabolic characteristics and its close relation to various neurological and psychiatric disorders.Recent research progresses have revealed a similar network in rodents,offering an excellent preclinical model that can improve our understanding of both physiology and pathophysiology of the human DMN.However,past research on DMN in rodents has mostly focused on metabolic signals and signal acquisitions under unnatural states,which greatly limited the studies of DMN in rodents.The current study collected electrophysiological data of DMN in freely behaving rats under three vigilance states: wakeful rest(WR),slow wave sleep(SWS),and rapid eye movement sleep(REMS).Using network analysis methods,this study examined three aspects of the rat DMN across vigilance states: local electroencephalogram(EEG)oscillation characteristics,features of functional network(including dynamic functional network),and features of effective network.This dissertation is organized as follows.First,EEG bands division of rat DMN across vigilance states.We divided the EEG frequency bands of the rat DMN across vigilance states using factor analysis,which clustered frequencies based on the covariant feature of their power spectral density(PSD).Results showed that the frequency band division varied across vigilance states and DMN regions.In specific,the θ(theta)oscillations were further divided into two bands during REMS corresponding to tonic and phasic stages,respectively.Two types of spindle activities with different frequency characteristics were also detected during different SWS stages,i.e.,high-voltage spindle(HVS)and low-voltage spindle(LVS),respectively.The results offered new insights into the neuronal oscillations of rat DMN across vigilance states,and motivated the follow-up studies by providing references to data selection and frequency division.Second,study on features of functional connectivity of electrophysiological rat DMN.This study analyzed the local activities and functional network features of the rat DMN based on the data of three vigilance states(e.g.,WR,SWS without HVS,tonic REMS)using PSD analysis and phase locking value(PLV)combined with modularity analysis.Results showed that the variations of local γ(gamma)power across vigilance states in rat DMN align with the metabolic changes of their human counterparts.Furthermore,the functional network features of rat electrophysiological DMN were similar to the findings in previous functional magnetic resonance imageing(fMRI)studies.Thus,the current study provides further electrophysiological evidence that rodent brains have a DMN similar to that in humans.Third,study on features of dynamic functional connectivity of electrophysiological rat DMN.This study analyzed the dynamic features of the rat DMN across vigilance states using both the sliding window analysis and factor analysis methods.Results found that the rat electrophysiological DMN is highly dynamic,and could be clustered into distinct spatial patterns.Interestingly,some of these patterns were state-dependent,while other patterns were independent across vigilance states.The temporal contributions of these patterns fluctuated across time,and were modulated by sleep.These spatial patterns with dynamic temporal contributions may offer a flexible framework that can integrate neuronal information efficiently to support cognition and behavior.These findings provide novel insights into the dynamic functional organization of the rat DMN.Fourth,study on features of effective connectivity of electrophysiological rat DMN.This research analyzed the effective connectivities within rat DMN across vigilance states using directed phase transfer entropy(dPTE)method.We observed well-organized anterior-to-posterior patterns of information flow within DMN in the δ(delta)band.However,an opposite pattern of posterior-to-anterior flow was found in the θ band.In specific,most of information senders in the δ band were receivers in the θ band,and vice versa,thus forming a frequency-specific information loop.Furthermore,such an opposite pattern was only observed in WR and tREMS.These frequency-dependent loops of anterior-posterior information flow may offer a reentrant mechanism for neuronal information integration,supporting conscious awareness.In summary,using network analysis methods,based on the electrophysiological data of freely behaving rats,the information integration function of rat DMN was studied from several aspects.The findings provide electrophysiological evidence for the existence of rat DMN,and offer novel insights into the information integration and consciousness maintenance of rat DMN.