British Journal of Anaesthesia
April 13, 2018
Phillip E. Vlisides, Tarik Bel‐bahar, Amanda Nelson et al.
117 citations
BackgroundDespite its designation as a 'dissociative anaesthetic,' the dissociative and psychoactive effects of ketamine remain incompletely understood. The goal of this study was to characterise the subjective experiences and accompanying EEG changes with subanaesthetic doses of ketamine.MethodsHigh-density EEG was recorded in 15 human volunteers before, during, and after subanaesthetic...
Frontiers in Human Neuroscience
February 16, 2018
Hyoungkyu Kim, Anthony G. Hudetz, Joseph W Y Lee et al.
The integrated information theory (IIT) proposes a quantitative measure, denoted as Φ, of the amount of integrated information in a physical system, which is postulated to have an identity relationship with consciousness. IIT predicts that the value of Φ estimated from brain activities represents the level of consciousness across phylogeny and functional states. Practical limitations, such as...
Frontiers in Neural Circuits
June 20, 2017
George A. Mashour, Anthony G. Hudetz
136 citations
There has been controversy regarding the precise mechanisms of anesthetic-induced unconsciousness, with two salient approaches that have emerged within systems neuroscience. One prominent approach is the "bottom up" paradigm, which argues that anesthetics suppress consciousness by modulating sleep-wake nuclei and neural circuits in the brainstem and diencephalon that have evolved to control...
Frontiers in Systems Neuroscience
March 23, 2017
Duan Li, Viviane S. Hambrecht‐Wiedbusch, George A. Mashour
33 citations
Recent data from our laboratory demonstrate that high-frequency gamma connectivity across the cortex is present during consciousness and depressed during unconsciousness. However, these data were derived from static and well-defined states of arousal rather than during transitions that would suggest functional relevance. We also recently found that subanesthetic ketamine administered during...
Anesthesia & Analgesia
June 23, 2016
Anthony G. Hudetz, George A. Mashour
128 citations
A quest for a systems-level neuroscientific basis of anesthetic-induced loss and return of consciousness has been in the forefront of research for the past 2 decades. Recent advances toward the discovery of underlying mechanisms have been achieved using experimental electrophysiology, multichannel electroencephalography, magnetoencephalography, and functional magnetic resonance imaging. By the...
PLoS Computational Biology
April 14, 2015
Joon-Young Moon, UnCheol Lee, Stefanie Blain-Moraes et al.
143 citations
The balance of global integration and functional specialization is a critical feature of efficient brain networks, but the relationship of global topology, local node dynamics and information flow across networks has yet to be identified. One critical step in elucidating this relationship is the identification of governing principles underlying the directionality of interactions between nodes....
Anesthesiology
September 21, 2013
Eduardo E. Icaza, George A. Mashour
11 citations
Abstract The psychedelic experience has been reported since antiquity, but there is relatively little known about the underlying neural mechanisms. A recent neuroimaging study on psilocybin revealed a pattern of decreased cerebral blood flow and functional disconnections that is surprisingly similar to that caused by various anesthetics. In this article, the authors review historical examples...
Anesthesiology
September 7, 2013
Heonsoo Lee, George A. Mashour, Gyu‐jeong Noh et al.
153 citations
INTRODUCTION: General anesthesia induces unconsciousness along with functional changes in brain networks. Considering the essential role of hub structures for efficient information transmission, the authors hypothesized that anesthetics have an effect on the hub structure of functional brain networks. METHODS: Graph theoretical network analysis was carried out to study the network properties of...
Proceedings of the National Academy of Sciences of the United States of America
August 27, 2013
Jimo Borjigin, UnCheol Lee, Tiecheng Liu et al.
The brain is assumed to be hypoactive during cardiac arrest. However, the neurophysiological state of the brain immediately following cardiac arrest has not been systematically investigated. In this study, we performed continuous electroencephalography in rats undergoing experimental cardiac arrest and analyzed changes in power density, coherence, directed connectivity, and cross-frequency...
PLoS One
August 15, 2013
Jeongkyu Shin, George A. Mashour, Seungwoo Ku et al.
16 citations
General anesthesia significantly alters brain network connectivity. Graph-theoretical analysis has been used extensively to study static brain networks but may be limited in the study of rapidly changing brain connectivity during induction of or recovery from general anesthesia. Here we introduce a novel method to study the temporal evolution of network modules in the brain. We recorded...
Proceedings of the National Academy of Sciences
June 10, 2013
George A. Mashour, Michael Alkire
148 citations
Are animals conscious? If so, when did consciousness evolve? We address these long-standing and essential questions using a modern neuroscientific approach that draws on diverse fields such as consciousness studies, evolutionary neurobiology, animal psychology, and anesthesiology. We propose that the stepwise emergence from general anesthesia can serve as a reproducible model to study the...
Anesthesiology
May 22, 2013
UnCheol Lee, Seungwoo Ku, Gyu‐jeong Noh et al.
436 citations
INTRODUCTION: Directional connectivity from anterior to posterior brain regions (or "feedback" connectivity) has been shown to be inhibited by propofol and sevoflurane. In this study the authors tested the hypothesis that ketamine would also inhibit cortical feedback connectivity in frontoparietal networks. METHODS: Surgical patients (n = 30) were recruited for induction of anesthesia with...
Frontiers in Psychology
2013
Neil Mehta, George A. Mashour
It is widely acknowledged that a complete theory of consciousness should explain general consciousness (what makes a state conscious at all) and specific consciousness (what gives a conscious state its particular phenomenal quality). We defend first-order representationalism, which argues that consciousness consists of sensory representations directly available to the subject for action...
Science Translational Medicine
February 22, 2012
George A. Mashour
The psychedelic drug psilocybin uncouples the activity of key brain areas, providing insight into new therapies for psychiatric disorders.
Anesthesia & Analgesia
April 23, 2011
George A. Mashour
12 citations
From Joseph in the book of Genesis to the 2010 blockbuster Inception, dreams have been a source of fascination. The attraction seems to derive, in part, from their bizarreness. Indeed, it is rare to hear someone muse that “I had the craziest wakefulness last night.” But we are also compelled by the allure that dreams are imbued with meaning or that they reveal something about our psyche....
Advances in Consciousness Research
October 28, 2010
Lucas Campos, Adrian Pichurko, George A. Mashour
We discuss the molecular and cognitive mechanisms of general anaesthesia and their relevance to the science of consciousness. General anaesthetics serve as an important tool to explore the transitions from conscious to unconscious processing, as these drugs rapidly induce a complete and reversible cessation of consciousness. With 40,000,000 patients undergoing general anaesthesia each year in...
Activitas Nervosa Superior
March 1, 2010
George A. Mashour, Ashley Turner
Abstract Consciousness is a multidisciplinary subject of inquiry. The extent of clinical contributions to the field of consciousness studies has yet to be investigated. The goal of this study was to assess the degree of clinically related articles in the literature of consciousness studies through a systematic evaluation. Three journals systematically identified (Consciousness and Cognition,...
The American Journal of Psychology
2010
Katherine MacDuffie, George A. Mashour
Understanding dreams has long been considered fundamental to the development of a theory of consciousness. Evidence from neurobiology and neuroimaging research has paved the way for new theories of dreaming that are empirically supported. In this article we argue that dreaming is a unique state of consciousness that incorporates 3 temporal dimensions: experience of the present, processing of...
Consciousness and Cognition
December 1, 2008
George A. Mashour, Eric LaRock
Philosophical (p-) zombies are constructs that possess all of the behavioral features and responses of a sentient human being, yet are not conscious. P-zombies are intimately linked to the hard problem of consciousness and have been invoked as arguments against physicalist approaches. But what if we were to invert the characteristics of p-zombies? Such an inverse (i-) zombie would possess all...
Nature Precedings
November 20, 2008
UnCheol Lee, Seunghwan Kim, Gyu‐jeong Noh et al.
33 citations
Abstract The cognitive unbinding paradigm suggests that the synthesis of cognitive information is attenuated by general anesthesia. Here, we investigated the functional organization of brain activities in the conscious and anesthetized states, based on characteristic functional segregation and integration of electroencephalography (EEG). EEG recordings were obtained from 14 subjects undergoing...
NeuroQuantology
September 4, 2007
George A. Mashour
17 citations
The cognitive binding problem is a central question in the study of consciousness: how does the brain synthesize its modal and submodal processing systems to generate a unity of conscious experience? This essay considers several solutions to the binding problem, as well as their shortcomings. In particular, the current theory of neural synchronization as the basis for binding and consciousness...
International Anesthesiology Clinics
2007
George A. Mashour
13 citations
University of Michigan Medical School Ann Arbor, Michigan A version of this article appeared in the Bulletin of Anesthesia History (July, 2005). The author thanks Dr Edward Lowenstein, Dr George Battit, Dr Bucknam McPeek, and Dr Warren Zapol of the Massachusetts General Hospital and Dr Johnathan Moreno of the University of Virginia for their interest and helpful contributions to this project....
Anesthesia & Analgesia
September 19, 2006
George A. Mashour
135 citations
The nature and mechanism of human consciousness is emerging as one of the most important scientific and philosophical questions of the 21st century. Disregarded as a subject of serious inquiry throughout most of the 20th century, it has now regained legitimacy as a scientific endeavor. The investigation of consciousness and the mechanisms of general anesthesia have begun to converge. In the...
Rui Dai, Hyunwoo Jang, Anthony G. Hudetz et al.
Understanding the relationship of conscious states to large-scale brain dynamics remains a central challenge in neuroscience. Here, diverse pharmacological and physiological perturbations, including psychedelic states, sleep, and propofol sedation, were used to examine integration-segregation organization of brain networks across altered states of consciousness in humans using functional MRI....