Anesthetics are known to disrupt neural interactions in cortical and subcortical brain circuits. While the effect of anesthetic drugs on consciousness is reversible, the neural mechanism mediating induction and recovery may be different. Insight into these distinct mechanisms can be gained from a systematic comparison of neural dynamics during slow induction of and emergence from anesthesia. To this end, we used functional magnetic resonance imaging (fMRI) data obtained in healthy volunteers before, during, and after the administration of propofol at incrementally adjusted target concentrations. We analyzed functional connectivity of corticocortical and subcorticocortical networks and the temporal autocorrelation of fMRI signal as an index of neural processing timescales. We found that en route to unconsciousness, temporal autocorrelation across the entire brain gradually increased, whereas functional connectivity gradually decreased. In contrast, regaining consciousness was associated with an abrupt restoration of cortical but not subcortical temporal autocorrelation and an abrupt boost of subcorticocortical functional connectivity. Pharmacokinetic effects could not account for the difference in neural dynamics between induction and emergence. We conclude that the induction and recovery phases of anesthesia follow asymmetric neural dynamics. A rapid increase in the speed of cortical neural processing and subcorticocortical neural interactions may be a mechanism that reboots consciousness.
Shamanic trance is an altered state of consciousness used by shamanic practitioners to glean information to be used for the physical, psychological, or spiritual healing of others. Despite shamanic practices dating back to the paleolithic era, few studies of this unique non-pharamacological state of consciousness have been conducted. In the largest study of shamanic practitioners to date, Huels et al. demonstrated that shamanic practitioners endure a variety of EEG changes during shamanic trance, with several of these correlating with self-reported changes in experience. Additionally, the self-reported changes in experience endured by shamanic practitioners are comparable to (and sometimes exceed) those induced by psychedelics.
Rest-task modulation of fMRI-derived global signal topography is mediated by transient coactivation patterns
Recent resting-state fMRI studies have shown that the global signal exhibits a nonuniform spatial distribution across gray matter, but is this informative? This neuroimaging study reveals novel insights into the informative nature of global signal by rest-task modulation of the global signal topography.
New fMRI study by Tanabe et al. published in the March 2020 issue of the journal Anesthesiology suggests that the global temporal coordination of neuronal activity across the entire brain is a unitary indicator of various states of consciousness including sleep, general anesthesia, and unresponsive wakefulness syndrome, whereas the relationship of the global and local brain activity defines the particular quality of each unconscious state.
The findings are recognized in numerous popular scientific new articles.
The study, led by neuroscientist Zirui Huang of the Center for Consciousness Science at the University of Michigan, suggests that the shifting balance between the Default Mode Network (DMN) and the Dorsal Attention network (DAT) of the brain may be a defining feature of consciousness.
Neuronal actitivity in the DMN is responsible for awareness of self whereas activity of the DAT is responsible for awareness of the environment. The two are in anticorrelation, meaning that they frequently alternate their engagement in overall brain activity. The participation of these networks is embedded in the transient activity of several other brain networks associated with other sensory, motor and cognitive functions. The dynamic transition among momentarily active networks is orderly and structured, which prompted the name “temporal circuit” in Huang’s paper.
Why the anticorrelated DMN and DAT are uniquely important to consciousness is evidenced by the brain activity maps obtained by functional magnetic resonance imaging (fMRI) of healthy anesthetized subjects and patients with disorders of consciousness. The DMN and DAT networks of unconscious individuals are largely isolated from the rest of the networks; they are simply not as accessible as they are during wakeful consciousness. This conclusion is further supported by the finding that DMN and DAT remain accessible (and anticorrelated) in psychiatric patients who are nevertheless conscious.
The paper was published in Science Advances:
accompanied by reviews in popular scietific news media:
Dr. Anthony G. (Tony) Hudetz has accepted the position as the new Director of the Center for Consciousness Science. He succeeds in this role Dr. George A. Mashour who has taken on a new role as Chair of the Department of Anesthesiology and Robert B. Sweet Professor of Anesthesiology. Dr. Mashour founded the Center for Consciousness Science in 2014 and will continue as the Scientific Director for the Center. He has been instrumental in advancing the CCS to a renowned center for consciousness research fostering cross-campus, national, and international collaborative studies of consciousness, leading-edge multidisciplinary approaches, and hosting annual symposia of high scientific impact and public interest. The exceptional leadership and vision of Dr. Mashour over the past five years is greatly appreciated.
The new Center Director, Dr. Hudetz, is currently Professor of Anesthesiology and Professor of Biomedical Engineering at U of M. He is the Director of Laboratory Research in the Department of Anesthesiology and is faculty in the Neuroscience Graduate Program and the Applied Physics Program. He has served as the Center’s Scientific Director for the past four years. Dr. Hudetz’s research focuses on the mechanistic relationship between consciousness and anesthesia using techniques in neurophysiology, FMRI, and computational modeling. His work has been funded by the NIH for twenty years.