| Recently decades,mind wandering is the hot topic in the cognitive neuroscience field.Since 2006 proposing the notion of mind wandering that integrated confusing name including spontaneous thought,task-unrelated thought,stimulus independent thought and daydreaming into one concept,a phenomenon that often spontaneously drift from the current task or working to internal thought,a body of papers have been published rapid.There are already 767 public mind wandering related researches by December 2016.A lot of daily awaking time of people are occupied by mind wandering that unrelated to the current working.Just like few knowledge we know about sleep time,however,people also do know a little about the meaning of mind wandering.The large-scale brain network view for cognitive neuroscience have opened up new research areas,and it is the current hot point.Numerous evidences indicate that cognition and behavior performance are not caused by the activation of isolated brain regions,but by the dynamic interaction between multiple large-scale brain networks.The functional connectivity technology is one of the main strategies and methods to reflect the ability of brain functional integration.At present,the neuroimaging research has proven and replicated claimed that mind wandering generates from the function of default mode network(DMN)of brain,and a widely co-activation in brain regions named default mode network occurs when people mind wandering.The general external direct tasks show more deactivation in DMN,however,more activation in DMN when mind wandering.The DMN is thought to support internally oriented and self-related mental processes,such as autobiographical memory,imaging the future,and theory of mind.By now,mind wandering is also a function of DMN.Based on the appearance of activation in DMN during mind wandering,a volume of resting-state fMRI focus on the study of functional connectivity among main nodes in DMN.They investigated the relationship between the dynamic interaction of functional networks and trait-level mind wandering,and neglected the action in whole brain during resting state.Some index could depict the resting-state brain including amplitude of low-frequency fluctuation(ALFF),fractional ALFF(f ALFF),regional homogeneity(Re Ho)and degree centrality(DC).It is necessary to examine the relationship between these indexes and trait-level mind wandering.Previous study found that except strong activation in DMN there are some activation in non-DMN brain regions such as dorsal anterior cingulate gyrus,bilateral dorsolateral prefrontal cortex and lingual gyrus and so on through SART paradigm with neuroimaging technology during mind wandering.Interestingly,most of these brain regions belong to the fronto-parietal network(FPN).It indicates that mind wandering need the action in DMN and the supplement of cognitive control function.Subsequently,a mate-analysis study found that a number of key DMN areas showed consistent recruitment across mind wandering studies,however,numerous non-DMN regions were also recruited including part of FPN regions,secondary somatosensory cortex and lingual gyrus and so on.These evidences suggest that DMN activation alone is insufficient to support mind wandering that need the cooperation between multiple large-scale networks.Unfortunately,although the co-activation of DMN and non-DMN regions have been interest of researchers,there still no one focus on the interaction and distribution pattern of functional brain networks during mind wandering and the relationship between them and mind wandering.The other study have proved that increased cooperation between the DMN and a fronto-parietal component of external attention system is associated with more rapid memory recollection.Meanwhile,the occipital lobe including lingual gyrus during mind wandering implicate that visual network(VS)is also playing an important role on supporting mind wandering,and VS is a very good indicator of visual stimuli processing.For the purpose of using a series of systematic analysis to fill the gap,we estimate the interaction between DMN and other large-scale brain networks in the present study.We expect that the deactivation of DMN and activation of FPN and VS would be observed during on-task state.But when it could be inverse during mind wandering.Regarding to previous studies,we also deduce that the interaction of brain networks would be benefit to behavioral performance of mind wandering.Some significant correlation among them would be found.In order to investigate the problem and verify the expectation as we mentioned above.The study one and study two in the present project separately recruited twenty-six and twenty-four individuals to complete resting-state and SART related functional MRI scans.Participants were instructed to pay attention on the targets and non-targets of SART showing on the screen,and they needed to maintain attention well.They must answer the questions according their real mental state while the probe occurs.In the study one,we estimated the relationship between ALFF/f ALFF/Re Ho/DC and the frequency of mind wandering under two conditions(with global signal or without global signal).We found that ALFF under two conditions are almost consistent with the other.Therefore,ALFF is a good index that to explore the association between trait-level mind wandering and resting-state brain.Frontal areas were negative correlated with mind wandering frequency to suppress mind wandering.The positive correlation with mind wandering frequency was found on the occipital lobe,it may be because of lots of visual imagery and event-related imaging during mind wandering.Other indexes were not stable.In the study two,we first verified previous findings that positive activity in DMN appeared during mind wandering,instead of positive activity of FPN and VS were observed during on-task.After that we compared the functional connectivity of each brain network during on-task and mind wandering.Relative to on-task state,the negative correlation of DMN-VS significantly decreased during mind wandering,and the positive correlation of FPN-VS significantly decreased,and there was a downtrend on the anti-correlation of FPN-DMN.It suggests that the antagonism between DMN and VS decreased and switched to cooperate with each other.The interaction of DMN-VS was significantly positive related to behavioral lapses during mind wandering.Meanwhile the connections of FPN and VS was fall.It implicate that FPN did not control VS to serve external orientation task well.There was significant negative relationship between FPN-VS and lapses during mind wandering indicating FPN began to inhibit the action of VS,which is conducive to maintain mind wandering.Module analysis suggested that brain functional regions become more diversity during mind wandering.In summary,interaction of functional networks and wandering regions are supporting mind wandering. |
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