EEG microstate dynamics indicate a U-shaped path to propofol-induced loss of consciousness

It is commonly believed that the stream of consciousness is not continuous but parsed into transient brain states manifesting themselves as discrete spatiotemporal patterns of global neuronal activity. Electroencephalographical (EEG) microstates are proposed as the neurophysiological correlates of these transiently stable brain states that last for fractions of seconds. To further understand the link between EEG microstate dynamics and consciousness, we continuously recorded high-density EEG in 23 surgical patients from their awake state to unconsciousness, induced by step-wise increasing concentrations of the intravenous anesthetic propofol. Besides the conventional parameters of microstate dynamics, we introduce a new method that estimates the complexity of microstate sequences. The brain activity under the surgical anesthesia showed a decreased sequence complexity of the stereotypical microstates, which became sparser and longer-lasting. However, we observed an initial increase in microstates' temporal dynamics and complexity with increasing depth of sedation leading to a distinctive U-shape that may be linked to the paradoxical excitation induced by moderate levels of propofol. Our results support the idea that the brain is in a metastable state under normal conditions, balancing between order and chaos in order to flexibly switch from one state to another. The temporal dynamics of EEG microstates indicate changes of this critical balance between stability and transition that lead to altered states of consciousness.

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Increased signal diversity/complexity of spontaneous EEG, but not evoked EEG responses, in ketamine-induced psychedelic state in humans

10.1101/508697 ◽

2019 ◽

Cited By ~ 2

Author(s):

Nadine Farnes ◽

Bjørn E. Juel ◽

André S. Nilsen ◽

Luis G. Romundstad ◽

Johan F. Storm

Keyword(s):

Brain Activity ◽

Altered States Of Consciousness ◽

Altered States ◽

Eeg Signal ◽

Eyes Closed ◽

Electrical Brain Activity ◽

States Of Consciousness ◽

Significant Difference ◽

Eyes Open ◽

Signal Diversity

AbstractObjectiveHow and to what extent electrical brain activity is affected in pharmacologically altered states of consciousness, where it is mainly the phenomenological content rather than the level of consciousness that is altered, is not well understood. An example is the moderately psychedelic state caused by low doses of ketamine. Therefore, we investigated whether and how measures of evoked and spontaneous electroencephalographic (EEG) signal diversity are altered by sub-anaesthetic levels of ketamine compared to normal wakefulness, and how these measures relate to subjective assessments of consciousness.MethodsHigh-density electroencephalography (EEG, 62 channels) was used to record spontaneous brain activity and responses evoked by transcranial magnetic stimulation (TMS) in 10 healthy volunteers before and after administration of sub-anaesthetic doses of ketamine in an open-label within-subject design. Evoked signal diversity was assessed using the perturbational complexity index (PCI), calculated from the global EEG responses to local TMS perturbations. Signal diversity of spontaneous EEG, with eyes open and eyes closed, was assessed by Lempel Ziv complexity (LZc), amplitude coalition entropy (ACE), and synchrony coalition entropy (SCE).ResultsAlthough no significant difference was found in the index of TMS-evoked complexity (PCI) between the sub-anaesthetic ketamine condition and normal wakefulness, all the three measures of spontaneous EEG signal diversity showed significantly increased values in the sub-anaesthetic ketamine condition. This increase in signal diversity also correlated with subjective assessment of altered states of consciousness. Moreover, spontaneous signal diversity was significantly higher when participants had eyes open compared to eyes closed, both during normal wakefulness and during influence of sub-anaesthetic ketamine doses.ConclusionThe results suggest that PCI and spontaneous signal diversity may be complementary and potentially measure different aspects of consciousness. Thus, our results seem compatible with PCI being indicative of the brain’s ability to sustain consciousness, as indicated by previous research, while it is possible that spontaneous EEG signal diversity may be indicative of the complexity of conscious content. The observed sensitivity of the latter measures to visual input seems to support such an interpretation. Thus, sub-anaesthetic ketamine may increase the complexity of both the conscious content (experience) and the brain activity underlying it, while the level, degree, or general capacity of consciousness remains largely unaffected.

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Intrinsic Brain Activity in Altered States of Consciousness

Annals of the New York Academy of Sciences ◽

10.1196/annals.1417.015 ◽

2008 ◽

Vol 1129 (1) ◽

pp. 119-129 ◽

Cited By ~ 221

Author(s):

M. Boly ◽

C. Phillips ◽

L. Tshibanda ◽

A. Vanhaudenhuyse ◽

M. Schabus ◽

...

Keyword(s):

Brain Activity ◽

Altered States Of Consciousness ◽

Altered States ◽

States Of Consciousness ◽

Intrinsic Brain Activity

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Altered states of consciousness in epilepsy: a DTI study of the brain

International Journal of Neuroscience ◽

10.1080/00207454.2016.1229668 ◽

2016 ◽

Vol 127 (8) ◽

pp. 667-672 ◽

Cited By ~ 4

Author(s):

Fangfang Xie ◽

Wu Xing ◽

Xiaoyi Wang ◽

Weihua Liao ◽

Wei Shi

Keyword(s):

Altered States Of Consciousness ◽

Altered States ◽

States Of Consciousness ◽

The Brain

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Whole-Brain Models to Explore Altered States of Consciousness from the Bottom Up

Brain Sciences ◽

10.3390/brainsci10090626 ◽

2020 ◽

Vol 10 (9) ◽

pp. 626 ◽

Cited By ~ 1

Author(s):

Rodrigo Cofré ◽

Rubén Herzog ◽

Pedro A.M. Mediano ◽

Juan Piccinini ◽

Fernando E. Rosas ◽

...

Keyword(s):

Brain Activity ◽

Generative Models ◽

Altered States Of Consciousness ◽

Global Changes ◽

Altered States ◽

Altered Consciousness ◽

Whole Brain ◽

Bottom Up ◽

States Of Consciousness ◽

Brain Models

The scope of human consciousness includes states departing from what most of us experience as ordinary wakefulness. These altered states of consciousness constitute a prime opportunity to study how global changes in brain activity relate to different varieties of subjective experience. We consider the problem of explaining how global signatures of altered consciousness arise from the interplay between large-scale connectivity and local dynamical rules that can be traced to known properties of neural tissue. For this purpose, we advocate a research program aimed at bridging the gap between bottom-up generative models of whole-brain activity and the top-down signatures proposed by theories of consciousness. Throughout this paper, we define altered states of consciousness, discuss relevant signatures of consciousness observed in brain activity, and introduce whole-brain models to explore the biophysics of altered consciousness from the bottom-up. We discuss the potential of our proposal in view of the current state of the art, give specific examples of how this research agenda might play out, and emphasize how a systematic investigation of altered states of consciousness via bottom-up modeling may help us better understand the biophysical, informational, and dynamical underpinnings of consciousness.

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Increased signal diversity/complexity of spontaneous EEG, but not evoked EEG responses, in ketamine-induced psychedelic state in humans

PLoS ONE ◽

10.1371/journal.pone.0242056 ◽

2020 ◽

Vol 15 (11) ◽

pp. e0242056

Author(s):

Nadine Farnes ◽

Bjørn E. Juel ◽

André S. Nilsen ◽

Luis G. Romundstad ◽

Johan F. Storm

Keyword(s):

Subjective Experience ◽

Brain Activity ◽

Altered States Of Consciousness ◽

Altered States ◽

Eeg Signal ◽

Eyes Closed ◽

States Of Consciousness ◽

Significant Difference ◽

Eyes Open ◽

Signal Diversity

How and to what extent electrical brain activity reflects pharmacologically altered states and contents of consciousness, is not well understood. Therefore, we investigated whether measures of evoked and spontaneous electroencephalographic (EEG) signal diversity are altered by sub-anaesthetic levels of ketamine compared to normal wakefulness, and how these measures relate to subjective experience. High-density 62-channel EEG was used to record spontaneous brain activity and responses evoked by transcranial magnetic stimulation (TMS) in 10 healthy volunteers before and during administration of sub-anaesthetic doses of ketamine in an open-label within-subject design. Evoked signal diversity was assessed using the perturbational complexity index (PCI), calculated from EEG responses to TMS perturbations. Signal diversity of spontaneous EEG, with eyes open and eyes closed, was assessed by Lempel Ziv complexity (LZc), amplitude coalition entropy (ACE), and synchrony coalition entropy (SCE). Although no significant difference was found in TMS-evoked complexity (PCI) between the sub-anaesthetic ketamine condition and normal wakefulness, all measures of spontaneous EEG signal diversity (LZc, ACE, SCE) showed significantly increased values in the sub-anaesthetic ketamine condition. This increase in signal diversity correlated with subjective assessment of altered states of consciousness. Moreover, spontaneous signal diversity was significantly higher when participants had eyes open compared to eyes closed, both during normal wakefulness and during influence of sub-anaesthetic ketamine. The results suggest that PCI and spontaneous signal diversity may reflect distinct, complementary aspects of changes in brain properties related to altered states of consciousness: the brain’s capacity for information integration, assessed by PCI, might be indicative of the brain’s ability to sustain consciousness, while spontaneous complexity, as measured by EEG signal diversity, may be indicative of the complexity of conscious content. Thus, sub-anaesthetic ketamine may increase the complexity of the conscious content and the brain activity underlying it, while the level or general capacity for consciousness remains largely unaffected.

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Consciousness: A Very Short Introduction

10.1093/actrade/9780198794738.001.0001 ◽

2017 ◽

Cited By ~ 2

Author(s):

Susan Blackmore

Keyword(s):

Neural Correlates ◽

Altered States Of Consciousness ◽

Altered States ◽

Short Introduction ◽

New Developments ◽

Brain Science ◽

States Of Consciousness ◽

The World ◽

Construction Of Self ◽

The Brain

Consciousness is ‘the last great mystery for science’. How can a physical brain create our experience of the world? What creates our identity? Do we really have free will? Could consciousness itself be an illusion? Exciting new developments in brain science are continuing these debates, and the field has now expanded to include biologists, neuroscientists, psychologists, and philosophers. Consciousness: A Very Short Introduction clarifies the potentially confusing arguments, and the major theories, whilst also outlining the amazing pace of neuroscience discoveries. Covering areas such as construction of self in the brain, mechanisms of attention, neural correlates of consciousness, and physiology of altered states of consciousness, it highlights the latest findings.

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The Stream of Consciousness: XV. James in Recent Context (1981–1986)

Imagination Cognition and Personality ◽

10.2190/8w9p-tgv9-c0am-m6ck ◽

1997 ◽

Vol 17 (2) ◽

pp. 123-140 ◽

Cited By ~ 4

Author(s):

Thomas Natsoulas

Keyword(s):

Present Article ◽

Special Interest ◽

Altered States Of Consciousness ◽

Objective Method ◽

Altered States ◽

Stream Of Consciousness ◽

Perceptual Awareness ◽

States Of Consciousness

Addressing work on consciousness published in this Journal allows me to bring relevant present-day material to bear on my ongoing exploration of James's stream. Instead of, as before, making use of an author's findings or ideas to improve our understanding of James's stream, I inquire into what each author has explicitly drawn from James's work in his or her article. I consider all fifteen published volumes of Imagination, Cognition and Personality in successive units of five, beginning with the first five years in this article. Of special interest are the specific ways present-day psychologists, who are strong on objective method, demonstrate or acknowledge the relevance to their work of the introspectively grounded propositions of their great predecessor. Discussed in the present article are theses belonging to five large topics: 1) the perception of reality, 2) conceiving of consciousness, 3) the emotions, 4) altered states of consciousness, and 5) discriminating imaginal from perceptual awareness.

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