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.
Trends in Neurosciences
November 1, 1996
N Block
120 citations
The author argues that access consciousness and phenomenal consciousness, though conceptually distinct, might refer to the same brain process, similar to how water and H2O are different concepts of the same substance. However, recent work by Crick and Koch suggests that these two forms of consciousness may have distinct, albeit overlapping, neural correlates, even though Crick and Koch themselves implicitly reject this possibility.
Trends in Neurosciences
December 21, 2020
Neil K. Savalia, Ling-Xiao Shao, Alex C. Kwan
110 citations
Ketamine and serotonergic psychedelics like psilocybin both relieve depression and promote neural plasticity, despite targeting different molecular receptors. This opinion article proposes a conceptual framework suggesting their actions converge at the dendrites, where they both enhance and suppress membrane excitability. Mismatches in these opposing effects may explain differences in cell-type and region selectivity, the compounds' moderate range of effects and toxicity, and their plasticity-promoting capacities.
Trends in Neurosciences
November 1, 2024
Cecilia Anna Brunello, Cecilia Cannarozzo, Eero Castrén
29 citations
Antidepressant drugs, including slow-acting types, fast-acting ketamine, and psychedelics, all promote neuronal plasticity through activation of BDNF signaling via its receptor TRKB, though each drug targets different cells. The authors propose that some antidepressants may directly bind to TRKB and allosterically enhance BDNF signaling. Activating TRKB in parvalbumin-containing interneurons disinhibits cortical networks and reopens a juvenile-like window of plasticity. This rewiring of faulty neural circuits, combined with environmental input, may explain clinical antidepressant effects. This hypothesis could guide development of new treatments.
Trends in Neurosciences
May 31, 2024
Andrea I. Luppi, Fernando E. Rosas, Pedro A. M. Mediano et al.
23 citations
Unconsciousness increases the coupling between brain structure and function across scales, while psychedelics may decouple brain function from structure. Anaesthetics, psychedelics, and disorders of consciousness can produce similar reconfigurations along the brain's unimodal-transmodal functional axis. Decomposing brain function into fundamental constituents of time, space, and information has driven recent advances in understanding consciousness and the brain's functional organisation. Computational modelling offers a path toward mechanistic integration, and decomposition approaches may help translate discoveries across species.
Trends in Neurosciences
October 1, 2024
Natalia Zaretskaya
2 citations
Spontaneous brain activity before a stimulus influences whether it is consciously perceived. The prefrontal cortex and default mode network play active roles in shaping perception, not just in higher-level cognition. The findings suggest that prestimulus neural states in multiple brain networks modulate sensory processing and conscious awareness.
Trends in Neurosciences
April 1, 2024
Célia Lacaux, Mélanie Strauss, Tristan A Bekinschtein et al.
The sleep-onset period (SOP), the transition from wakefulness to sleep, has been largely overlooked despite its potential importance. This review synthesizes current knowledge about the SOP in humans, examining its definition and limits, the dynamic electrophysiological changes that accompany falling asleep, and the interplay between internal and external processing during this transition. The authors propose that the SOP may offer cognitive benefits and identify novel directions for better diagnosing sleep-onset disorders. The review highlights recent findings that have reignited interest in this transitional period, shedding light on its neural mechanisms, cognitive dynamics, and clinical implications.
Trends in Neurosciences
December 1, 2023
Jaan Aru, Matthew E Larkum, James M Shine
Large language models are unlikely to become conscious because they lack three key features of biological consciousness. First, they do not receive the embodied, real-world sensory information that grounds human experience. Second, their architectures miss essential neural structures of the mammalian thalamocortical system linked to awareness. Third, the evolutionary and developmental processes that produced conscious living organisms—rooted in survival-driven action and multi-level cellular processes—have no counterpart in current artificial systems.
Trends in Neurosciences
June 1, 2023
Jaan Aru, M. Larkum, J. Shine
Claims that large language models may soon be conscious are difficult to defend from a neuroscience perspective. The inputs to these models lack the embodied, embedded information content that characterizes sensory contact with the world. Present-day AI architectures also miss key features of the thalamocortical system linked to conscious awareness in mammals. Furthermore, the evolutionary and developmental trajectories that produced living conscious organisms have no parallels in current artificial systems. The existence of living organisms depends on actions and survival, which are linked to multi-level cellular, inter-cellular, and organismal processes that culminate in agency and consciousness.
Trends in Neurosciences
September 1, 2021
Rufin Vanrullen, Ryota Kanai
Deep learning has brought artificial intelligence close to human performance on many tasks, but new brain-inspired architectures are still needed. The Global Workspace Theory describes a large-scale system that integrates and distributes information among specialized modules to support higher-level cognition and awareness. The authors argue it is now time to implement this theory explicitly with deep-learning techniques. They propose a roadmap using unsupervised neural translation between multiple latent spaces—neural networks trained on different tasks or sensory modalities—to create a single, amodal Global Latent Workspace (GLW). The potential functional advantages of GLW and its neuroscientific implications are reviewed.
Trends in Neurosciences
April 1, 2009
Javier González-Maeso, Stuart C. Sealfon
Research on psychedelics like LSD and dissociative drugs such as PCP has converged with studies of schizophrenia, as their effects mimic core symptoms of the disorder. Some atypical antipsychotics were identified by their high affinity for serotonin 5-HT(2A) receptors, the same target as LSD-like drugs. Effects of PCP-like drugs are strongly influenced by modulation of both 5-HT(2A) and metabotropic glutamate 2/3 receptors. A serotonin-glutamate receptor complex in cortical pyramidal neurons may be the target of both psychedelics and certain antipsychotics. Recent findings on receptor, signaling, and circuit mechanisms could unify the serotonin and glutamate neurochemical hypotheses of schizophrenia.
Trends in Neurosciences
June 1, 2001
F R Sharp, M Tomitaka, M Bernaudin et al.
Non-competitive NMDA receptor antagonists like phencyclidine, ketamine, and MK801 cause psychosis in humans and damage the cingulate-retrosplenial cortex in adult rodents. This damage can be prevented by GABA-receptor agonists and antipsychotics such as haloperidol and clozapine. Injecting MK801 into the anterior thalamus reproduces the cortical injury, while injecting GABA-receptor agonists there prevents injury from systemic MK801. The authors suggest that inhibiting NMDA receptors on GABAergic thalamic reticular nucleus neurons may activate thalamocortical circuits that cause injury in animals and psychosis in humans, potentially contributing to schizophrenia.