Intrinsic Organization of the Anesthetized Brain

Abstract

The neural mechanism of unconsciousness has been a major unsolved question in neuroscience despite its vital role in brain states like coma and anesthesia. The existing literature suggests that neural connections, information integration and conscious states are closely related. Indeed, alterations in several important neural circuitries and networks during unconscious conditions have been reported. However, how the whole-brain network is topologically reorganized to support different patterns of information transfer at unconscious states remains unknown. Here we directly compared whole-brain neural networks in an awake and an anesthetized state in rodents. Consistent with our previous report, the awake rat brain was organized in a non-trivial manner and conserved fundamental topological properties as the human brain. Strikingly, these topological features were well maintained in the anesthetized brain. Meanwhile, local neural networks were reorganized with altered local network properties. The connectional strength between brain regions was also considerably different between the awake and anesthetized conditions. Interestingly, we found that long-distance connections were not preferentially reduced in the anesthetized condition, arguing against the hypothesis that loss of long-distance connections is characteristic to unconsciousness. These findings collectively show that the integrity of the whole-brain network can be conserved between widely dissimilar physiologic states while local neural networks can flexibly adapt to new conditions. They also illustrate that the governing principles of intrinsic brain organization might represent fundamental characteristics of the healthy brain. With the unique spatial and temporal scales of rsfMRI, this study has opened a new avenue for understanding the neural mechanism of (un)consciousness.

Small-world characteristics of EEG patterns in post-anoxic encephalopathy

“…Our finding that differences in small-world characteristics exist between survivors and nonsurvivors and correlate with outcome also supports the functional difference between coma induced by anesthesia (21,22) and anoxia. Further analyses in the temporal domain could elucidate possible differences in neural synchronization and desynchronization (34,35) between those patients who regain consciousness and those who do not.…”

Functional network study on the wild type and DISC1 transgenic mice

“…This is in agreement with preserved small-worldness reported by rs-fMRI studies on anaesthetized and awake rats, as well as mice under medetomidine (Liang et al, 2011(Liang et al, , 2012bMechling et al, 2014). These observations indicate that small-worldness is an intrinsic property of functional networks in mice.…”

“…This organization implied strong inter-connections between these cortical areas. A similar module was reported in awake rat brain containing visceral cortex, gustatory cortex, primary and supplemental somatosensory areas, but also motor cortex and insular cortex (Liang et al, 2012b). The difference may be caused by the anaesthetic depths and/or experimental procedures.…”

“…In awake rat, one study reported that the retrosplenial cortex was a single functional module. In contrast, it was not reported in any module under isoflurane anaesthesia (Liang et al, 2012b). These results implied that retrosplenial cortex might have dynamic roles in rodent functional networks.…”

“…Altered structures of functional networks are observed in normal developmental processes, aging, different mental illness and anaesthetized states (Wang et al, 2010a;Liang et al, 2012b). Graph topology provides abundant insightful evidence for researchers to understand brain functions.…”