Frontiers in Systems Neuroscience
August 14, 2019
Vincent Bonhomme, Cécile Staquet, Javier Montupil et al.
109 citations
General anesthesia reversibly alters consciousness without globally shutting down the brain. Depending on the agent and dose, it can produce a complete absence of subjective experience (unconsciousness), a conscious experience without environmental perception (disconnected consciousness, like during dreaming), or oriented consciousness with environmental awareness (connected consciousness). Each state may be followed by explicit or implicit memories. Progress in brain function exploration has improved understanding of neural correlates of consciousness and their alterations during anesthesia, including changes in functional and effective brain connectivity, consciousness network topology, and spatio-temporal dynamics.
Frontiers in Systems Neuroscience
March 23, 2017
Duan Li, Viviane S. Hambrecht‐Wiedbusch, George A. Mashour
33 citations
High-frequency gamma connectivity across the cortex is present during consciousness and depressed during unconsciousness. Subanesthetic ketamine (25 mg/kg) administered during isoflurane anesthesia accelerates recovery upon discontinuation of the primary anesthetic and increases gamma power during emergence. In rodents, ketamine reduced emergence time by 44%. During accelerated emergence, frontal-parietal coherence and normalized symbolic transfer entropy in high-frequency gamma bandwidth were increased compared with saline-treated controls. Surrogates of cortical information exchange in high-frequency gamma are increased in association with accelerated recovery from anesthesia, suggesting a functional significance of high-gamma information transfer in consciousness.
Frontiers in Systems Neuroscience
March 21, 2022
Andrea Zaccaro, Andrea Piarulli, Lorenza Melosini et al.
32 citations
Slow nasal breathing at 2.5 breaths per minute, as practiced in Pranayama, alters brain activity and induces a non-ordinary state of consciousness, primarily through mechanical stimulation of the olfactory epithelium rather than through vagal nerve stimulation. In 12 experienced meditators, slow nasal breathing produced slowing of EEG delta and theta activity in prefrontal regions, widespread increases in theta and high-beta connectivity, increased phase-amplitude coupling between these bands in prefrontal and posterior Default Mode Network regions, and increased small-worldness of high-beta networks. Participants reported a higher perception of being in a non-ordinary state of consciousness compared to mouth breathing at the same rate or resting state.
Frontiers in Systems Neuroscience
May 25, 2023
Charles Gervais, Louis-Philippe Boucher, Guillermo Martinez Villar et al.
25 citations
The healthy conscious brain is thought to operate near a critical state, balancing order and chaos for optimal information processing. This scoping review of 49 studies across seven altered states of consciousness (ASC)—including disorders of consciousness, sleep, anesthesia, epilepsy, psychedelics, delirium, and meditation—found that each category showed a deviation from this critical state. Most studies could identify a deviation but not its direction; however, a preliminary consensus indicates non-REM sleep reflects a subcritical state, epileptic seizures a supercritical state, and psychedelics are closer to criticality than normal waking consciousness. The evidence is limited and methodologically varied, but criticality may become an objective way to characterize ASC and guide treatments, such as using anesthesia or psychedelics to restore criticality in pathological brain states.
Frontiers in Systems Neuroscience
July 1, 2016
Arto eAnnila
18 citations
The brain, as an open thermodynamic system, consumes free energy in the least time across all its processes, from cellular metabolism to cognition and consciousness. This principle, derived from statistical mechanics, treats cognitive operations as identical in organizational principle to other natural processes, emerging along path-dependent, non-determinate trajectories. Consciousness integrates neural networks for coherent free-energy consumption—meaningful action—and the entire hierarchy of systems can be summed up as thermodynamic entropy. The theory also acknowledges awareness in other systems at different levels of nature's hierarchy.
Frontiers in Systems Neuroscience
August 11, 2020
Michael A. Brito, Duan Li, George A. Mashour et al.
15 citations
Ketamine and propofol anesthesia both reduce cortical complexity, but in different frequency bands. Using Lempel-Ziv complexity (LZc) to analyze electroencephalographic data from rats, the study found that ketamine anesthesia significantly reduced complexity in the high gamma range (65–175 Hz), while propofol anesthesia reduced complexity in lower frequencies (0.5–55 Hz). During emergence from ketamine anesthesia, complexity increased in broadband and low-frequency ranges. After normalizing for spectral influences, the reductions during anesthesia remained significant, indicating they are genuine neurophysiological features. The findings suggest that reduced high gamma complexity is a specific marker of ketamine anesthesia.
Frontiers in Systems Neuroscience
August 5, 2025
Dotun Adeleye Adeyinka, Donelson R. Forsyth, Suzanne Currie et al.
7 citations
Psilocybin, from Psilocybe mushrooms, shows promise for treating neurodegenerative and psychiatric disorders like major depressive disorder by promoting neuroprotection, neurogenesis, and neuroplasticity. It may help combat mild neurodegeneration by increasing synaptic density and supporting neuronal growth, with low addiction risk and few adverse effects. Animal models, including Drosophila and fish, have provided insights into its mechanisms, aiding high-throughput screening of neural development, behavior, and genetic pathways. While mammalian models are needed for pharmacokinetics and complex nervous system interactions, small non-mammalian models help identify early targets. This complementary approach suggests psilocybin could potentially halt or reverse neurodegenerative processes.
Frontiers in Systems Neuroscience
January 22, 2026
Gordana Dodig-Crnkovic
1 citation
Cognition is not limited to organisms with nervous systems but is an organizational property of all living systems, from single cells to complex animals. Living systems engage in learning, memory, and goal-directed behavior by transforming information embodied in their physical structures and interactions with the environment. This info-computational (ICON) framework views these processes as present from the start of life, becoming more integrated and temporally extended with increasing biological complexity. It explains how complex cognition, awareness, and mind arise from basic life-regulatory dynamics and generates testable implications for basal cognition, developmental biology, and embodied artificial systems.
Frontiers in Systems Neuroscience
July 1, 2026
Kei Torii, Maho Jinno
Ketamine's effects vary across patients and sessions, so dose alone does not explain them. A Gate-Amplifier-Reintegration framework proposes that awake low-dose ketamine amplifies transient network flexibility, while autonomic-salience stability acts as a Gate that may steer this flexibility toward reintegration or dysphoric dissociation. The three-step sequence involves Gate (candidate autonomic-salience stability), Amplifier (ketamine under conditions preserving vigilance), and Reintegration (organizing flexibility into language, attention, and action). Heart-rate variability serves as a peripheral state-verification proxy. The framework is informed by nonrandomized clinical observations from a single-center outpatient chronic pain care pathway, which provide clinical provenance but not comparative efficacy evidence. Falsifiable predictions include prospective Gate manipulation altering pre-dose autonomic state and randomized designs testing mediation of tolerability and clinical change.
Frontiers in Systems Neuroscience
June 4, 2026
Elena Bondi, Flavia Carbone, Giandomenico Schiena et al.
People with affective disorders (ADs) show emotional processing deficits involving disrupted brain network activity, especially in default mode and fronto-temporal circuits with abnormal theta and alpha oscillations. This exploratory study used virtual reality (VR) scenarios to induce awe—a self-transcendent emotion that may reduce rumination and boost positive affect—while recording EEG in ADs and healthy controls (HCs). HCs exhibited high awe responses with scenario-specific modulations in alpha and theta band activity and connectivity, indicating preserved cognitive flexibility.
Frontiers in Systems Neuroscience
December 1, 2021
Minkyung Kim, Hyoungkyu Kim, Zirui Huang et al.
The brain's ability to switch between internal and external modes is crucial for generating models of self and world, and this switching may rely on a state near criticality—a balanced condition between order and disorder. Large synchronization fluctuations of brain networks near criticality create temporal windows that favor either integrating internal information or processing external stimuli. Using computational modeling, EEG, and fMRI analyses across altered states of consciousness, synchronized networks bias toward internal information while incoherent networks bias toward external information. These preferences are most prominent at criticality and in conscious states associated with 4–12 Hz bandwidth.
Frontiers in Systems Neuroscience
October 25, 2019
Wolf Singer
The hard problem of consciousness—explaining how subjective experience arises from material brain processes—cannot be solved by studying neural correlates alone. Instead, the problem can be addressed within a naturalistic evolutionary framework that includes both biological and socio-cultural dimensions. Perceptions, including self-perception, are constructed based on prior knowledge. Social interactions among cognitively capable agents generate immaterial social or cultural realities that become new priors. These priors shape a self-model with both material and immaterial aspects, experienced as veridical because they are implicit and not consciously accessible. Thus, the hard problem appears as a cognitive construct amenable to naturalistic explanation.
Frontiers in Systems Neuroscience
August 30, 2019
Jaan Aru, Mototaka Suzuki, R. Rutiku et al.
A fundamental feature of consciousness is that its contents depend on its state. The authors propose that both state and contents depend on the activity of cortical layer 5 pyramidal (L5p) neurons. These neurons couple cortico-cortical and thalamo-cortical loops, forming a thalamo-cortical broadcasting system where L5p cells are central. This coupling corresponds to the coupling between state and contents of consciousness. The perspective predicts that cortical processing without L5p neurons will be unconscious, suggesting L5p neurons have a central role in the mechanisms underlying consciousness.