Nature reviews. Neuroscience
July 1, 2022
Anil K. Seth, Tim Bayne
836 citations
Four prominent theoretical approaches to consciousness are reviewed: higher-order theories, global workspace theories, re-entry and predictive processing theories, and integrated information theory. Each theory's key characteristics are described, including which aspects of consciousness they explain, their neurobiological commitments, and supporting empirical data. The review considers how empirical debates might distinguish among these theories and outlines three ways theories need to be developed for rigorous testing. Iterative development, testing, and comparison of these theories is expected to deepen understanding of consciousness.
Trends in Cognitive Sciences
April 22, 2016
Tim Bayne, Jakob Hohwy, Adrian M. Owen
443 citations
The concept of a level of consciousness is central to the science of consciousness, used to describe global states in post-comatose disorders, epileptic absence seizures, anesthesia, and sleep. However, what a level of consciousness actually means remains unclear. This paper argues that the levels-based framework for understanding global states of consciousness is untenable and instead proposes a multidimensional account of global states.
Neuroscience of Consciousness
January 1, 2018
Tim Bayne, Olivia Carter
153 citations
The popular and academic claim that the psychedelic state is a 'higher' state of consciousness is critically examined. The article distinguishes between conscious contents and global states, reviewing lab-based findings on psilocybin and LSD. While some aspects of consciousness are enhanced, many functional capacities are seriously compromised. The authors argue that because psychedelics affect different dimensions of consciousness in opposing ways, the unidimensional 'level-based' view of consciousness is unsupported; instead, a multidimensional conception is strongly supported. The analysis also considers implications for Global Workspace Theory and Integrated Information Theory.
Trends in Neurosciences
December 10, 2019
Tim Bayne, Anil K. Seth, Marcello Massimini
146 citations
Consciousness might persist in brain tissue that is fully causally isolated from the body and environment, forming an 'island of awareness'—a conscious state neither shaped by sensory input nor able to produce motor output. This opinion paper examines three potential cases: ex cranio brains (brains kept alive outside the body), the disconnected hemisphere after hemispherotomy surgery, and cerebral organoids (lab-grown brain tissue). The authors discuss methods for detecting consciousness in such disconnected brains, noting that current detection tools rely on sensory or motor interaction and may not apply. They argue that discovering islands of awareness would have profound ethical and legal implications and would challenge theories holding that consciousness requires embodiment or interaction with the world.
Neuropsychology Review
May 12, 2020
Edward H.F. de Haan, Paul M. Corballis, Steven A. Hillyard et al.
86 citations
Cutting the corpus callosum (split-brain) broadly disrupts functional integration across perception and attention, but some processes like action control remain unified. The key unresolved question is whether split-brain patients have split or unified consciousness. Current evidence is insufficient to decide, and future studies may need to consider intermediate conceptualizations beyond a simple yes or no.
Neuropsychologia
September 17, 2021
Elizabeth Schechter, Tim Bayne
11 citations
A critical evaluation of recent split-brain experiments argues that claims of unified consciousness in patient D.D.C. are premature. Two distinct conceptions of unity of consciousness are distinguished: agency-based and experience-based. Whether the behavioral data demonstrate unity of agency remains an open question, depending on both the mechanisms underlying split-brain behavior and what constitutes a single agent. Even if agency-based unity is established, the data are difficult to reconcile with full unity of consciousness in the experience-based sense.
PLoS Biology
October 1, 2025
Michele Angelo Colombo, Jacopo Favaro, Ezequiel Mikulan et al.
7 citations
After hemispherotomy surgery for epilepsy, which disconnects an entire brain hemisphere, the isolated cortex shows brainwave patterns typical of deep sleep or anesthesia, not wakefulness. In 10 pediatric patients, EEG recordings revealed prominent slow oscillations and a steeper spectral decay in the disconnected hemisphere, while the connected hemisphere maintained normal waking patterns. These sleep-like patterns persisted years after surgery, suggesting the isolated cortex likely lacks awareness.
Acta paediatrica (Oslo, Norway : 1992)
February 1, 2025
Joel Frohlich, Tim Bayne
3 citations
Consciousness in infants is likely present by 5 months of age or earlier, based on a cluster of behavioral and neural markers validated in adults that can be translated to infancy. Historically, infants were operated on without anesthesia, but attitudes shifted in the 1990s toward taking consciousness seriously. Since infants cannot report experiences, no single marker suffices, so a consensus across multiple markers pointing to the same developmental period provides a convincing argument. This cluster-based approach reviews the most promising markers for early consciousness.
The Oxford Handbook of the Philosophy of Consciousness
July 9, 2020
Tim Bayne
2 citations
Conscious thought, though often neglected, has been the subject of philosophical inquiry centered on three key issues: what types of mental states qualify as conscious thought and how they might be categorized; whether the consciousness of thought is fundamentally different from other forms of consciousness; and whether consciousness is essential to thought or merely an accidental feature. This chapter offers an opinionated introduction to these debates, exploring possible taxonomies, the nature of cognitive consciousness, and the relationship between consciousness and thought.
Trends in Cognitive Sciences
June 1, 2026
Patrick Butlin, Robert Long, Tim Bayne et al.
A method for assessing whether AI systems might be conscious is presented, drawing on existing neuroscientific theories of consciousness. The approach involves deriving indicators from such theories to inform beliefs about AI consciousness. This method can make progress because computational functionalist theories, which are influential, have empirically testable implications for AI. The work does not claim that any current AI is conscious but outlines a rigorous framework for future assessment.
Trends in Cognitive Sciences
March 1, 2024
Tim Bayne, Anil K. Seth, Marcello Massimini et al.
New tests for consciousness (C-tests) are urgently needed to resolve uncertainty about when consciousness arises in human development, when it is lost due to neurological disorders and brain injury, and how it is distributed in nonhuman species. This need is amplified by recent developments in AI, neural organoids, and xenobot technology. Existing C-tests are of limited use, and no tests exist for many critical populations. The paper identifies challenges facing any attempt to develop C-tests, proposes a multidimensional classification of such tests, and identifies strategies for validating them.
Trends in Cognitive Sciences
October 1, 2023
Tim Bayne, Joel Frohlich, R. Cusack et al.
Evidence from studies of functional network connectivity, attention, multimodal integration, and cortical responses to global oddballs suggests that consciousness is likely present in early infancy and may even occur before birth. Recent research is beginning to provide clues about both the content and structure of infant consciousness.
Neuroimage
June 1, 2023
Joel Frohlich, Tim Bayne, Julia S Crone et al.
Consciousness likely cannot begin before the establishment of thalamocortical connectivity at 26 weeks gestation, as this system is necessary for subjective experience according to most theoretical frameworks. To determine when consciousness emerges after this point, the authors advocate developing a sensory perturbational complexity index (sPCI) using auditory, visual, or olfactory cortical perturbations—rather than electromagnetic ones—to estimate the perinatal brain's state of consciousness. Techniques such as fMRI, EEG, and MEG can be used in both newborn and fetal studies, with the womb offering a more controlled environment than the cradle for such investigations.
Neuroscience of Consciousness
January 1, 2018
Tim Bayne
The integrated information theory (IIT) is a prominent scientific framework for studying consciousness and developing a consciousness meter. This paper critically examines the axiomatic method that IIT's creators use. The author argues that the method is open to multiple interpretations and that none of IIT's five alleged axioms can play the required role: each either fails to be truly axiomatic or fails to impose a substantive constraint on a theory of consciousness. The article concludes by outlining an alternative methodology for the science of consciousness, called the natural kind approach.
Oxford Handbooks Online
September 5, 2013
Tim Bayne
The normal unity of consciousness may fragment or break down in psychiatric disorders. This chapter examines how different forms of unity of consciousness can be lost in conditions like multiple personality disorder, schizophrenia, and depersonalization.
Encyclopedia of Cognitive Science
January 15, 2006
Tim Bayne
Consciousness is unified in multiple respects, yet there is ongoing disagreement about what this unity consists in and what grounds it. Resolving this debate is expected to clarify the fundamental nature of experience, the self, and certain disorders of consciousness.