Large-scale brain functional modularity is reflected in slow electroencephalographic rhythms across the human non-rapid eye movement sleep cycle

What Is Lost During Dreamless Sleep: The Relationship Between Neural Connectivity Patterns and Consciousness

“…Reorganisation of modules was observed in N2 and N3, and modularity decreased immediately after participants were awoken (Tagliazucchi et al, 2013b). Spoormaker and colleagues (2010) also examined modularity in their study and reported an increase in local clustering in SWS, in line with the previously discussed studies (Tagliazucchi et al, 2013b). Taken together, these findings suggest that during deep NREM sleep, functional integration in the cortex is reduced.…”

EEG Functional Connectivity Prior to Sleepwalking: Evidence of Interplay Between Sleep and Wakefulness

“…Since our data reveal that this lower connectivity is found locally rather than over anterior and posterior electrodes, it may be interpreted as a decrease in local connectivity. Because SWS is characterized by high local connectivity, [21][22][23][24] our findings prior to episode onset likely reflect a transition towards wakefulness or, at the very least, a lighter sleep stage. While results in the delta band show decreased connectivity in posterior areas, a completely different portrait was observed in higher frequency bands, where posterior regions show increased connectivity over a wide antero-posterior bilateral network.…”

“…20 Testing the hypothesis that impaired consciousness during NREM sleep is associated with increased modularity in brain activity, fMRI studies have shown that NREM sleep is characterized by a decrease of large-scale networks and increase of smaller independent modules as reflected by high clustering ratios and low inter-modular connectivity. [21][22][23][24] Using transcranial magnetic stimulation (TMS) and high density (HD) EEG to assess how a TMS pulse delivered to the premotor cortex propagates in the brain during both sleep and wakefulness, Massimini and colleagues 25 found that when compared to a wakefulness propagated response, the response during NREM sleep (as recorded with HD-EEG) was stronger but extinguished more rapidly and did not propagate beyond the stimulation site. Thus, the fading of consciousness observed during deeper sleep stages may be related to a breakdown in long-range cortical connectivity.…”

“…In support of this hypothesis, total brain connectivity is negatively correlated to SWA during NREM sleep 23 and a direct link has been described between increased EEG delta power and a breakdown in inter-modular connectivity. 24 Given this collection of findings, the investigation of functional connectivity in relation to somnambulism appears both promising and warranted. In fact, the results of one recent study 26 suggest that when compared to NREM sleep of healthy controls, the NREM sleep of adults presenting with a disorder of arousal (eg, sleep terrors or sleepwalking) is characterized by the presence of local sleep differences in EEG SWA power, even in the absence of clinical episodes.…”

Breakdown of long-range temporal dependence in default mode and attention networks during deep sleep

“…In particular, the default mode network (DMN; a set of task-deactivated regions implied with internal conscious cognitive processes) (9, 10) was repeatedly observed during deep sleep, albeit with reduced frontal connectivity (11,12). Although brain modules are preserved, even in the absence of conscious awareness, their functional integration is greatly impaired (8,13,14), which was predicted by an information integration account of consciousness (15). These results suggest that ongoing conscious mentation is not the only origin of RSN activity, whereas the level of consciousness is reflected in the interaction of functional networks.…”