Coactive Micropattern Analysis On The Electrophysiological Default Mode Network

The default mode network(DMN)is one of the most important brain networks,and plays critical roles in maintaining the internal balance in human brain.However,the studies on DMN functions are mostly based on the non-invasive neural imaging technology,such as the functional magnetic resonance imaging(f MRI)and the scalp electroencephalogram(EEG),which could not provide high spatial-temporal neural activity for DMN and further lead to the limitations for the investigations on DMN fast dynamics.Revealing the DMN dynamics is important for the further understanding of DMN functions,and become one of the research hotspots in the field of neuroscience.It has been reported that rat brains also have the DMN,of which the structure and functions are similar to that in human brain,providing an excellent animal model for tracking the fast dynamics of DMN activity.Thus,in this dissertation,we conducted our work on the dynamics and physiological significance of rat DMN neural activity through the implantable electrophysiological recordings.To this purpose,we proposed a novel coactive micropattern(CAMP)analysis method to track the activity patterns and the connectivity patterns of rat DMN with high spatial-temporal resolutions.This dissertation is organized as follows:First,we proposed the CAMP analysis method,which was sutiable for the dynamic analysis of neural signals with high temporal resolution,to investigate the alterations of DMN dynamics during wakefulness and sleep.Our results showed that there were three basic kinds of CAMPs during rat DMN activity,including the common low-activity level micropattern(cDMN),the anterior high-activity level micropattern(aDMN)and the posterior high-activity level micropattern(pDMN).All these CAMPs displayed stable spatial structures during the wakefulness and sleep,while the temporal features and the transition structures of them were distinct in different states of wakefulness.In the AWAKE state,there existed a dynamic balance among these CAMPs.However,in the slow wave sleep(SWS)state,the cDMN became the main activity pattern of DMN,and the transition probabilities between cDMN with other two CAMPs increased.In the rapid eye movement(REM)sleep state,the aDMN and pDMN were the major activity patterns with increased transition probabilities among themselves.According to these findings,we proposed a three-state model based on the three CAMPs,which could describe the alterations of DMN activity during wakefulness and sleep,and indicate the neural physiological relationships between DMN activity with states of wakefulness.Second,we further proposed the CAMP network analysis method to track the dynamics of DMN connectivity in different states of wakefulness.Based on the distribution of CAMPs,we constructed three CAMP networks from DMN activity during wakefulness and sleep,including the common default mode micropattern network(cDMmN),the anterior default mode micropattern network(aDMmN)and the posterior default mode micropattern network(pDMmN).It could be observed that there was no difference in the network connectivity and properties among three CAMP networks.In the SWS state,the connectivities of aDMmN and pDMmN were higher than those of cDMmN.However,the cDMmN became the network structure with highest network connectivity,indicating that the functional role of three CAMP networks were different.Besides,we found that the alterations of network connectivity of three CAMP networks were similar during the switching of wakefulness levels,indicating that the changes of wakefulness levels had general impacts on DMN activity.Third,we investigated the influence of sleep deprivation on rat DMN dynamics during sleep with the general CAMP method.Our findings suggested that the sleep deprivation mainly disrupted DMN dynamics in the SWS state.It showed that the occurrency probability of cDMN increased,while that of pDMN decreased after sleep deprivation.Moreover,the transition structures among CAMPs reorganized and all the CAMP networks displayed significantly increased network connectivity and efficiency.However,the DMN dynamics in the REM sleep state remained after sleep deprivation.Our results implied the distinct impacts of sleep deprivation on different sleep states,and demonstrated the underlying mechanism of sleep deprivation on DMN dynamics in the SWS state.Last,we employed the general CAMP method on the investigation of the DMN dynamics in human brain.In this study,we reconstructed the DMN source activity from the scalp EEG with the e LORETA algorithm.Then,the general CAMP method was applied to reveal the abnormality of DMN source activity in the obsessive compulsive disorder(OCD)patients.We found that there also existed three CAMPs in the DMN dynamics of normal subjects,consisting of the cDMN,aDMN and pDMN.However,in OCD patients,there were four kinds of CAMPs in the DMN dynamics,where the pDMN were separated into the left posterior high-activity level micropattern(L-pDMN)and the right posterior high-activity level micropattern(R-pDMN).Additionally,the temporal features of cDMN and aDMN were decreased,suggesting the abnormality of DMN dynamics in OCD patients.Further investigations found that,the cDMmN and aDMmN in OCD patients under different frequency bands showed increased connectivity than those in normal subjects.Besides,the posterior cingulate cortex and the superior frontal cortex were the hub DMN regions in OCD patients during the increasement of CAMP network connectivity.Our findings illustrated the neural mechanism of abnormal DMN dynamics in OCD patients,and provided new biomarkers for the diagnosis of OCD in clinical.In summary,this dissertation proposed the novel general CAMP method for tracking the dynamics of multi-channels neural activity.The general CAMP method decomposed the CAMPs from neural dynamics,and constructed the transition structure of CAMPs to describe the dynamics of neural activity,offering a new method for understanding the dynamic mechanisms of brain activity.Based on the general CAMP method,we found that there existed three kinds of CAMPs in both human and rat DMN dynamics,revealing the cross-species similarity of DMN neural activity structure.Moreover,we also demonstrated the specificity of DMN dynamics in different states of wakefulness,and revealed the neural mechanism under the alteration of DMN dynamics during the switching of wakefulness levels.Our work will help provide new biomarkers for finding the DMN characteristics in the brian disease,and has obvious scientific significance and potential clinical value.