Thinking about consciousness

Interest in the neurobiological substrates of consciousness has risen dramatically over the last few decades. This is reflected both in the steady increase in the number of papers published and in the recent surge of adversarial collaborations, in which researchers with opposing assumptions join forces to develop experiments to settle controversies and advance the field. Given this progress, we are enthusiastic to present this Neuron special issue on consciousness, with numerous reviews and commentaries each addressing a different area of consciousness research. While it becomes clear that the reported neural correlates of consciousness largely vary with the aspect of consciousness being investigated, the articles highlight the complexity of the topic and why achieving a better understanding of consciousness is critical beyond academic discussions: for example, from an ethical perspective regarding the detection of consciousness in patients under anesthesia or in a state of coma, in non-human animals, in infants, or even in artificial systems. The first review article by Storm et al. provides an overview of five current theories of consciousness. The authors synthesize the convergences of these partially competing and seemingly contradictory theories. They advocate for an integration-oriented approach and, ultimately, for a unified theory of consciousness. The following three pieces review the neural mechanisms underlying anesthesia, sleep, and post-coma recovery, respectively. Although these conditions reflect different states of arousal, they are all accompanied by an alteration or even loss of consciousness, hopefully followed by the regaining of full awareness. George Mashour reviews evidence from multiple species for the suppression of consciousness by various anesthetic drugs. He highlights that the orchestration of neural activity across cortical and subcortical circuits is necessary to suppress and recover consciousness during and after anesthesia. Tononi et al. discuss the neural mechanisms mediating dreamless and dreaming sleep. These different stages of sleep are characterized by different states of consciousness and are also associated with different neural substrates. Nicholas Schiff presents recent developments in the recovery of consciousness following coma and the promise of using different technologies for potential treatment options. The next two articles each focus on one subcortical and one cortical structure, respectively, which play crucial roles in modulating the states of consciousness. While the thalamus and the prefrontal cortex are important nodes, they need to act in concert with other nodes within a neural network serving consciousness. Whyte et al. review the influence of the thalamus on not only the state but also the content of consciousness via complex interactions with the cortex. Theofanis Panagiotaropoulos discusses the contribution of the prefrontal cortex to conscious awareness as evident from visual perception paradigms such as binocular rivalry. A question of the utmost importance across disciplines ranging from neuro-ethics to AI is when we become conscious. In her Neuroview, Claudia Passos-Ferreira tackles this topic by reviewing behavioral and neuroimaging studies in newborn infants. Although experimental paradigms and verbal reports are limited in this population, she argues that newborn infants are indeed conscious. In the final review of this special issue, Mudrik et al. share their perspective on the advantages of increasing the ecological validity of consciousness research by introducing more "real-life" experiments in the lab, which would facilitate the generalization of the findings. Lastly, we are excited to present Q&As with two pioneers of the modern era of consciousness neuroscience: Christof Koch and Stanislas Dehaene. Koch and Dehaene share their opinions on the consciousness field at large, past developments, and potential future directions. While this special issue can only showcase some of the fascinating areas of consciousness research, we hope that this collection of articles inspires reflection, new ideas and experimental paradigms, and collaborative scrutiny. We agree that much progress has been made over the past few decades, and the future looks bright for resolving some of the mysteries surrounding the neuroscience of consciousness. Anesthesia and the neurobiology of consciousnessGeorge A. MashourNeuronApril 4, 2024In BriefIn the 19th century, the discovery of general anesthesia revolutionized medical care. In the 21st century, anesthetics have become indispensable tools to study consciousness. Here, I review key aspects of the relationship between anesthesia and the neurobiology of consciousness, including interfaces between sleep and anesthetic mechanisms, anesthesia and primary sensory processing, the effects of anesthetics on large-scale functional brain networks, and mechanisms of arousal from anesthesia. I discuss the implications of data derived from the anesthetized state for the science of consciousness, then conclude with outstanding questions, reflections, and future directions. Full-Text PDF An integrative, multiscale view on neural theories of consciousnessStorm et al.NeuronMarch 5, 2024In BriefConsciousness theories are hotly debated but can be misaligned in scope or approach, fueling discussions centered on differences. Storm et al. argue that some seemingly insurmountable disagreements can instead be interpreted as complementary in an integrative neurobiological view on consciousness. Full-Text PDF Open AccessStanislas DehaeneStanislas DehaeneNeuronMay 15, 2024In BriefStanislas Dehaene is a cognitive neuroscientist elucidating the biological mechanisms that give rise to human perception and cognition. In a conversation with Neuron, he talks about his ongoing interest in consciousness research, the role of theory in neuroscience, and his current work on education and the science of learning. Full-Text PDF Toward an interventional science of recovery after comaNicholas D. SchiffNeuronMay 15, 2024In BriefHere, Nicholas Schiff reviews several entry points for innovations aimed at recovery of consciousness after coma. Opportunities for rescuing latent capacities in partially damaged human neurons are considered across a range of recoveries from coma to chronic cognitive impairment. Full-Text PDF Can we detect consciousness in newborn infants?Claudia Passos-FerreiraNeuronMay 15, 2024In BriefConscious experiences in infants remain poorly understood. In this NeuroView, Passos-Ferreira discusses recent evidence for and against consciousness in newborn babies. She argues that the weight of evidence from neuroimaging and behavioral studies supports the thesis that newborn infants are conscious. Full-Text PDF Taking consciousness for real: Increasing the ecological validity of the study of conscious vs. unconscious processesMudrik et al.NeuronApril 22, 2024In BriefIn this perspective, Mudrik et al. call for more naturalistic studies of consciousness, given the artificial nature of most experimental manipulations. Despite the entailed challenges, they argue that this will increase ecological validity, generate new questions, and yield stronger effects. Full-Text PDF Open AccessAn integrative view of the role of prefrontal cortex in consciousnessTheofanis I. PanagiotaropoulosNeuronMay 15, 2024In BriefIn this review, Panagiotaropoulos reviews empirical evidence suggesting that the prefrontal cortex (PFC) plays a critical role in consciousness. In particular, the convergence of multiple phenomena related to consciousness in the PFC suggests its integrative role. Full-Text PDF Consciousness and sleepTononi et al.NeuronMay 1, 2024In BriefThe paper by Tononi et al. discusses what sleep reveals about the substrate of consciousness, how experience can vanish during sleep, and how dreams can be supported by a brain largely disconnected from the environment, unreflective, and forgetful. Full-Text PDF Thalamic contributions to the state and contents of consciousnessWhyte et al.NeuronMay 15, 2024In BriefCellular and systems neuroscience points to a thalamic contribution to consciousness. Matrix-thalamocortical loops support wakefulness and perceptual threshold, and core-thalamocortical loops maintain content and enable perceptual constancy. The mesoscale architecture of these loops may explain general properties of conscious contents. Full-Text PDF Open AccessChristof KochChristof KochNeuronMay 15, 2024In BriefIn this talk with Neuron, Christof Koch, a physicist and neuroscientist, advocates for a pragmatic program to track the footprints of consciousness in the brain and for team science, explains the recent pseudo-controversy regarding integrated information theory of consciousness, and speaks about the joy of exploring the mysteries around us. Full-Text PDF