Unresponsiveness ≠ unconsciousness

Remifentanil stabilizes hemodynamics with modulating subthalamic beta oscillation during deep brain stimulation

General anesthesia is a promising method for advanced Parkinson's disease patients unable to tolerate awake deep brain stimulation (DBS) surgery. However, anesthetic agents must be kept at relatively low levels to preserve the quality of intraoperative microelectrode recordings, which can lead to unstable hemodynamic conditions. Remifentanil, with its sedative and analgesic properties, could offer a solution. This study retrospectively analyzed microelectrode recordings of the subthamic nucleus (STN) and hemodynamic responses in patients with Parkinson's disease who received deep brain stimulation surgery under controlled volatile anesthesia with/without remifentanil infusion. From October 2017 to June 2019, 24 patients with Parkinson's disease who received bilateral subthalamic deep brain stimulation surgery in Hualien Tzu Chi Hospital with (n = 12) or without remifentanil infusion (n = 12) were enrolled in this study. We conducted a comprehensive spike analysis, examining frequency, inter-spike interval properties, modified burst index, modified pause index, and modified pause ratio. Additionally, we performed spike frequency spectrum analysis to investigate oscillatory activity in high-frequency, multi-unit, and single-unit neuronal activity. Our findings revealed no differences in STN firing characteristics, while a significant decrease in high beta power was observed in multi-unit activity in the remifentanil group. Notably, nine patients in the non-remifentanil group required additional nicardipine, whereas none in the remifentanil group did. Conclusively, for patients with advanced Parkinson's disease sensitive to external stimulation at low minimum alveolar concentration, remifentanil co-administration is an option to avoid unstable hemodynamic conditions during subthalamic deep brain stimulation surgery.

Connectome harmonic decomposition tracks the presence of disconnected consciousness during ketamine-induced unresponsiveness

BACKGROUND

Ketamine, in doses suitable to induce anaesthesia in humans, gives rise to a unique state of unresponsiveness accompanied by vivid experiences and sensations, making it possible to disentangle the correlated but distinct concepts of conscious awareness and behavioural responsiveness. This distinction is often overlooked in the study of consciousness.

METHODS

The mathematical framework of connectome harmonic decomposition (CHD) was used to view functional magnetic resonance imaging (fMRI) signals during ketamine-induced unresponsiveness as distributed patterns across spatial scales. The connectome harmonic signature of this particular state was mapped onto signatures of other states of consciousness for comparison.

RESULTS

An increased prevalence of fine-grained connectome harmonics was found in fMRI signals obtained during ketamine-induced unresponsiveness, indicating higher granularity. After statistical assessment, the ketamine sedation harmonic signature showed alignment with signatures of LSD-induced (fixed effect =0.0113 [0.0099, 0.0127], P<0.001) or ketamine-induced (fixed effect =0.0087 [0.0071, 0.0103], P<0.001) psychedelic states, and misalignment with signatures seen in unconscious individuals owing to propofol sedation (fixed effect =-0.0213 [-0.0245, -0.0181], P<0.001) or brain injury (fixed effect =-0.0205 [-0.0234, -0.0178], P<0.001).

CONCLUSIONS

The CHD framework, which only requires resting-state fMRI data and can be applied retrospectively, has the ability to track alterations in conscious awareness in the absence of behavioural responsiveness on a group level. This is possible because of ketamine's unique property of decoupling these two facets, and is important for consciousness and anaesthesia research.

Spatiospectral dynamics of electroencephalography patterns during propofol-induced alterations of consciousness states

Altered consciousness induced by anesthetics is characterized by distinct spatial and spectral neural dynamics that are readily apparent in the human electroencephalogram. Despite considerable study, we remain uncertain which brain regions and neural oscillations are involved, as well as how they are impacted when consciousness is disrupted. The experimental data was obtained from the open-access dataset, which contains pre-processed EEG data recorded from 20 healthy participants during propofol sedation. Using unsupervised machine learning methods (i.e., non-negative matrix factorization, NMF), we investigated the spatiospectral dynamic evolution of brain activity from awake to sedation and back induced by propofol in healthy research volunteers. Our methods yielded six dynamical patterns that continuously reflect the neural activity changes in specific brain regions and frequency bands under propofol sedation. Temporal dynamic analyses showed that differences in alpha oscillation patterns were less pronounced in response group than drowsy group, with hemispheric asymmetry in posterior occipital lobe over the course of the sedation procedure. We designed an index 'hemispheric lateralization modulation of alpha [HLM(α)]' to measure asymmetry during awake state and predicting individual variability in propofol-induced alterations of consciousness states, obtaining prediction AUC of 0.8462. We present an alpha modulation index which characterizes how these patterns track the transition from awake to sedation as a function of increasing dosage. Our study reveals dynamics indices that track the evolution of neurophysiological of propofol on brain circuits. Analyzing the spatiospectral dynamics influenced by propofol provides valuable understanding of the mechanisms of these agents and strategies for monitoring and precisely controlling the level of consciousness in patients under sedation and general anesthesia.

General anaesthesia decreases the uniqueness of brain functional connectivity across individuals and species

The human brain is characterized by idiosyncratic patterns of spontaneous thought, rendering each brain uniquely identifiable from its neural activity. However, deep general anaesthesia suppresses subjective experience. Does it also suppress what makes each brain unique? Here we used functional MRI scans acquired under the effects of the general anaesthetics sevoflurane and propofol to determine whether anaesthetic-induced unconsciousness diminishes the uniqueness of the human brain, both with respect to the brains of other individuals and the brains of another species. Using functional connectivity, we report that under anaesthesia individual brains become less self-similar and less distinguishable from each other. Loss of distinctiveness is highly organized: it co-localizes with the archetypal sensory-association axis, correlating with genetic and morphometric markers of phylogenetic differences between humans and other primates. This effect is more evident at greater anaesthetic depths, reproducible across sevoflurane and propofol and reversed upon recovery. Providing convergent evidence, we show that anaesthesia shifts the functional connectivity of the human brain closer to the functional connectivity of the macaque brain in a low-dimensional space. Finally, anaesthesia diminishes the match between spontaneous brain activity and cognitive brain patterns aggregated from the Neurosynth meta-analytic engine. Collectively, the present results reveal that anaesthetized human brains are not only less distinguishable from each other, but also less distinguishable from the brains of other primates, with specifically human-expanded regions being the most affected by anaesthesia.

Noradrenergic suppression to reduce electroencephalographic arousal after intubation: a randomised, placebo-controlled trial

Background

Intraoperative awareness, without explicit recall, occurs after induction of anaesthesia in approximately 10% of persons under 40 yr of age. Most anaesthetic agents minimally suppress the noradrenergic system. We hypothesised that addition of dexmedetomidine, which suppresses noradrenergic activity, may reduce encephalographic (EEG) arousal in response to tracheal intubation; such an effect would lay the foundation for future studies of dexmedetomidine in reducing intraoperative awareness.

Methods

A single-site randomised, placebo-controlled trial with sex-based stratification was conducted. Participants, aged 18-40 yr old, undergoing intubation for general anaesthesia were eligible for recruitment and randomly allocated to receive dexmedetomidine or placebo. Dexmedetomidine (0.5 μg kg-1) was given as a 5-min loading dose before induction. Bispectral index (BIS) values were collected during the induction phase of anaesthesia and the isolated forearm technique was used to assess patients' responsiveness before and after tracheal intubation. The primary outcome was the effect of dexmedetomidine on changes in BIS from pre-to postintubation.

Results

A total of 51 patients were recruited and included in the primary analysis. We did not observe an effect of dexmedetomidine on changes in BIS after tracheal intubation (mean difference -1.13, 95% confidence interval [CI] -4.87 to 2.62; p=0.556). Dexmedetomidine reduced the estimated plasma propofol concentration at loss of responsiveness (difference [dexmedetomidine - placebo]: -1.06 μg ml-1, 95% CI -1.66 to -0.46; p<0.001) and before intubation (difference [dexmedetomidine - placebo]: -1.84 μg ml-1, 95% CI -2.79 to -0.90; p<0.001). There was one patient in the placebo group who gave positive responses in the isolated forearm test before and after tracheal intubation.

Conclusions

Dexmedetomidine demonstrated an anaesthetic-sparing effect at induction of anaesthesia but did not prevent EEG arousal after tracheal intubation, as defined by an increase in the BIS value.

Clinical Trial Registration

Australia and New Zealand Clinical Trials Registry (Trial ID: ACTRN12622000754741).

The relationship of bispectral index values to conscious state: an analysis of two volunteer cohort studies

BACKGROUND

The ability of current depth-of-anaesthesia monitors to differentiate subtle changes in the conscious state has not been well characterised. We examine the variability in bispectral index (BIS) scores associated with disconnected conscious and unconscious states as confirmed by a novel serial awakening paradigm.

METHODS

Seventy adult participants, given propofol or dexmedetomidine, had a cumulative 1381 electroencephalographic (EEG) recordings across two centres. Participants were awakened periodically, and their recent conscious experience interrogated by structured questioning. BIS were reconstructed from EEG using openibis, and the distribution of BIS scores were compared using linear mixed effects modelling. The predictive capacity of BIS across states of consciousness was also examined.

RESULTS

Reconstructed BIS scores correlated significantly with blood concentrations of propofol and dexmedetomidine (all P<0.001). However, while the average BIS was different between baseline wakefulness (mean BIS=95.1 [standard deviation=3.5]); connected consciousness with drug present (84.0 [10.9]); disconnected consciousness (70.0 [16.9]); and unconsciousness (68.1 [16.1]), the interquartile range of these states (3.6, 15.1, 23.3 and 26.8, respectively) indicated high degrees of overlap and individual variability. Connected consciousness could be differentiated from either disconnected consciousness or unconsciousness with 86% accuracy (i.e. 14% error rate), and disconnected consciousness differentiated from unconsciousness with 74% accuracy.

CONCLUSIONS

These results agree with previous studies that BIS scores fail to reliably differentiate between states of consciousness, exacerbated by segregating connected, disconnected, and unconscious states. To develop a method that reliably identifies the conscious state of an individual (not an average), work is needed to establish the causal mechanisms of disconnection and unconsciousness.

Efficacy of intranasal dexmedetomidine-esketamine sedation for pediatric acceptance of facemask: single-center, double-blind, randomized, controlled trial

OBJECTIVE

We compare the efficacy of intranasal dexmedetomidine (DEX) and DEX-esketamine sedation on pediatric acceptance of face mask.

METHODS

This single-center double-blind randomized controlled study was conducted at a tertiary hospital affiliated with Shanghai Jiao Tong University. Ninety children aged 1 year to 6 years old and scheduled for elective surgery were randomly allocated in a 1:1 ratio into receiving DEX alone (n = 45) and DEX-esketamine (n = 45). DEX and esketamine were used intranasally at doses of 2 µg/kg and 2.0 mg/kg respectively. Children were assessed by an attending anesthesiologist with modified observer's assessment of alertness and sedation (MOAA/S), pediatric separation anxiety scale (PSAS) and mask acceptance scale (MAS). Perioperative adverse events (bradycardia, hypotension, hypoxia, emergence delirium etc.) were recorded.

RESULTS

Of 95 patients enrolled, 90 completed the study. The proportion of children who accepted facemask was significantly higher in the DEX-esketamine group compared to the DEX group (86.7% (39/45) vs. 62.2% (28/45), p = 0.008). Within 30 min after intranasal administration of agents, PSAS scores were similar between the two groups. Children in the DEX group were easily aroused when repositioned from the transferring bed to the operation table. In contrast, those in the DEX-esketamine group maintained a stable level of sedation (MOAA/S scores, median [25th- 75th interquartile range], 1 [1, 1] for DEX-esketamine vs. 2 [1, 4] for DEX, p < 0.001). Furthermore, subgroup analysis found that DEX-esketamine provided better facemask acceptance in children with high anxiety (PSAS ≥ 3). There were no significant differences in perioperative heart rate, noninvasive blood pressure and percutaneous arterial oxygen saturation between the two groups. Postoperative extubation time and perioperative adverse events were also comparable between the groups (all p > 0.05).

CONCLUSIONS

For preoperative sedation, combination of DEX with esketamine improved mask acceptance than dexmedetomidine alone, likely due to its superior anxiolytic effect in children with high anxiety.

TRIAL REGISTRATION

This study was registered in the Chinese Clinical Trial Register (registration no. ChiCTR2400087873, registration date on 6/8/2024).

Effect of Intraoperative Midazolam on Postoperative Delirium in Older Surgical Patients: A Prospective, Multicenter Cohort Study

BACKGROUND

Midazolam is a short-acting benzodiazepine frequently used in the perioperative setting. This study aimed to investigate the potential impact of intraoperative midazolam on postoperative delirium in older patients undergoing noncardiac surgery.

METHODS

This study included patients aged 65 yr and older who received general anesthesia between April 2020 and April 2022 in multiple hospitals across China. Postoperative delirium occurring within 7 days was assessed using the 3-min Diagnostic Interview for Confusion Assessment Method. Univariable and multivariable logistic regression models based on the random effects were used to determine the association between midazolam administration and the occurrence of postoperative delirium, presented as the risk ratio and 95% CI. A Kaplan-Meier cumulative incidence curve was plotted to compare the distribution of time to postoperative delirium onset between patients who received midazolam and those who did not. Subgroup analyses based on specific populations were performed to explore the relationship between midazolam and postoperative delirium.

RESULTS

In all, 5,663 patients were included, of whom 723 (12.8%) developed postoperative delirium. Univariate and multivariable logistic regression analyses based on random effects of different hospitals showed no significant association between midazolam medication and postoperative delirium among older population (unadjusted risk ratio, 0.96; 95% CI, 0.90 to 1.30; P = 0.38; and adjusted risk ratio, 1.09; 95% CI, 0.91 to 1.33; P = 0.35). The Kaplan-Meier curve showed no difference in the distribution of time to postoperative delirium onset (hazard ratio, 1.02; 95% CI, 0.88 to 1.18; P = 0.82). The results of subgroup analyses found that intraoperative midazolam treatment was not associated with postoperative delirium in the specific subgroups of patients.

CONCLUSIONS

Intraoperative administration of midazolam may not be associated with an increased risk of postoperative delirium in older patients undergoing noncardiac surgery.

Effects of ketamine and propofol on muscarinic plateau potentials in rat neocortical pyramidal cells

Propofol and ketamine are widely used general anaesthetics, but have different effects on consciousness: propofol gives a deeply unconscious state, with little or no dream reports, whereas vivid dreams are often reported after ketamine anaesthesia. Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist, while propofol is a γ-aminobutyric-acid (GABAA) receptor positive allosteric modulator, but these mechanisms do not fully explain how these drugs alter consciousness. Most previous in vitro studies of cellular mechanisms of anaesthetics have used brain slices or neurons in a nearly "comatose" state, because no "arousing" neuromodulators were added. Here we tested mechanisms of anaesthetics in rat medial prefrontal cortex (mPFC) slices after bath-applying the cholinergic agonist muscarine to partly mimic an "aroused-like" state, using whole-cell patch-clamp recordings from layer 2/3 pyramidal cells (L2/3PCs). According to leading theories of access consciousness and working memory, L2/3PCs are particularly important for these cognitive functions. We found that muscarine induced long-lasting depolarising plateau potentials (PPs) and spiking following brief depolarising current injections in the L2/3PCs. After 2 hours of pre-incubation with ketamine or propofol, the muscarine-induced PPs were altered in seemingly different ways: 3 μM propofol reduced the PPs and (significantly) spiking, whereas 20 μM ketamine seemed to enhance PPs and spiking (non-significantly). Brief wash-in of these drug concentrations failed to induce such effects, probably due to insufficient equilibration by diffusion in the slices. In contrast, pre-incubation with a high dose (100 μM) of ketamine suppressed the PPs and spiking. We discuss whether the apparently different effects on PPs may possibly be related to contrasting clinical effects: ketamine causing atypical anaesthesia with vivid, "psychedelic" dreaming while propofol causes less dreaming.

Neuroscience of coma

Coma and disorders of consciousness are frequently considered in terms of two linked anatomic-functional systems: the arousal system and the awareness system. The mesopontine tegmentum (namely the cuneiform/subcuneiform nuclei of the caudal midbrain and the pontis oralis nucleus of the rostral pons) and the monoamine nuclei generate signals of arousal. These signals are augmented in lateral hypothalamus and basal forebrain, which then project to the thalamus and diffusely across the cortex. The medial dorsal tegmental tract is the main conduit for the ascending arousal system to directly activate the thalamic intralaminar nuclei and modulate thalamocortical networks, while the lateral dorsal tegmental tract connects to the thalamic reticular nucleus for regulation of intrathalamic inhibitory networks. The central thalamus (particularly the intralaminar nuclei) and the mesocircuit regulate the arousal system. Lesions to any part of this system, particularly paramedian and bilateral lesions, result in a depressed level of arousal. Distinct from the arousal pathways, the awareness system runs continuously as a stream of consciousness. It consists of large-scale distributed cortical networks that are necessary for representations of the external (executive control network with the dorsal/ventral attention networks) and the internal world (executive control network in conjunction with the default network). A feature of the awareness system is that it does not capture external and internal worlds at once and instead, holds singular representations, serially moment-by-moment. The medial dorsal nucleus of the thalamus serves as the associative nuclei of the default network, and the thalamic reticular nucleus regulates the awareness system. Lesions that disrupt large-scale networks, particularly nodes of cortical hubs, result in lack of awareness. Integrative paradigms such as the integrated information theory and the global neuronal workspace models are attempts to bind awareness and arousal into a unified experience of consciousness.

The Curing Coma Campaign: A platform for advancing science and clinical care worldwide

Recovery from coma or impaired consciousness is often the central issue in acute neurologic conditions such as traumatic brain injury, hypoxic-ischemic brain injury, stroke, and central nervous system infections. Recent advances in the science underpinning acute disorders of consciousness (DoC) have also served to highlight further scientific gaps and the lack of a coordinated approach to improving care for these patients. The Curing Coma Campaign (CCC) was initiated by the Neurocritical Care Society in 2019 as a platform to bring together the scientific, clinical, and public communities to cohesively address this issue. Comprised of various modules and working groups focused on aspects including fundamental science, prospective clinical studies, ethics, care of the coma patient, and engagement and community, initial efforts of the CCC have ranged from developing strategies for biomarker development to creating World Coma Day as an opportunity for widespread interaction. To achieve the goal of relevance across different geographic and resourced environments, the CCC implemented specific considerations to ensure equity and generalizability. These include international representation of patients in research studies, attention to assessments and interventions that can be implemented in resource-limited settings, and recognition of the impact of culture on the care of DoC patients.

Research progress on the depth of anesthesia monitoring based on the electroencephalogram

General anesthesia typically involves three key components: amnesia, analgesia, and immobilization. Monitoring the depth of anesthesia (DOA) during surgery is crucial for personalizing anesthesia regimens and ensuring precise drug delivery. Since general anesthetics act primarily on the brain, this organ becomes the target for monitoring DOA. Electroencephalogram (EEG) can record the electrical activity generated by various brain tissues, enabling anesthesiologists to monitor the DOA from real-time changes in a patient's brain activity during surgery. This monitoring helps to optimize anesthesia medication, prevent intraoperative awareness, and reduce the incidence of cardiovascular and other adverse events, contributing to anesthesia safety. Different anesthetic drugs exert different effects on the EEG characteristics, which have been extensively studied in commonly used anesthetic drugs. However, due to the limited understanding of the biological basis of consciousness and the mechanisms of anesthetic drugs acting on the brain, combined with the effects of various factors on existing EEG monitors, DOA cannot be accurately expressed via EEG. The lack of patient reactivity during general anesthesia does not necessarily indicate unconsciousness, highlighting the importance of distinguishing the mechanisms of consciousness and conscious connectivity when monitoring perioperative anesthesia depth. Although EEG is an important means of monitoring DOA, continuous optimization is necessary to extract characteristic information from EEG to monitor DOA, and EEG monitoring technology based on artificial intelligence analysis is an emerging research direction.

Conscious experiences during non-rapid eye movement sleep parasomnias

Disorders of Arousal (DOA) are non-rapid eye movement (NREM) parasomnias traditionally regarded as unconscious states. However, recent research challenges this assumption. This narrative review aims to explore the presence and qualitative features of conscious experiences in patients with DOA during their episodes. The literature indicates a higher recall of conscious experiences during DOA episodes than previously believed, estimated at about 50-60 % in adults (immediately post-episode). Data on children are limited but suggest a lower recall rate (<30 % when interviewed retrospectively). Patient reports range from brief scenic fragments to elaborate scenarios with plot development, often fraught with negative emotions and misfortunes and with considerable correspondence between subjective experiences and observed behaviors. In many of the described cases, patients appear to enact their dreams, entering a hallucinatory state where internally generated images overlay external percepts. The potential implications for clinical management, research endeavors, and legal considerations regarding nocturnal violence, along with existing limitations and controversial points, are discussed.

Anesthesiologists and Capital Punishment

Physician professional organizations in all Western countries consistently hold that it is unethical for physicians to participate in judicial executions. Physician participation in capital punishment is of particular concern for anesthesiologists, who have been identified by the courts as ideal candidates to participate in executions, particularly lethal injection executions. Arguments in favor of participation are based on flawed interpretations of the ethical principle of double-effect, mistaken analogies with physician aid-in-dying, and ignore evidence of prisoner suffering in the execution process. The American Board of Anesthesiology will investigate and may sanction diplomates who participate in executions by revoking their board certification.

Acceptability of bispectral Index monitoring in end-of-life care for dementia

BACKGROUND

Assessing consciousness might benefit the care for people with Alzheimer's disease and other types of dementia at the end of life by indicating distressing symptoms and moments of awareness. This could guide symptom control and increase interaction with the person with dementia.

OBJECTIVE

This study aims to investigate the acceptability of a biosignal measurement of consciousness, the Bispectral Index monitoring (BIS), for persons with dementia at the end of life.

METHODS

Qualitative study using focus groups and interviews with demonstrations of BIS monitoring, with 17 individuals with dementia and 24 family caregivers. Qualitative content analysis was based on the theoretical framework of acceptability.

RESULTS

People with dementia did not find BIS monitoring bothersome, yet acceptability varied across participants and situations. Family caregivers considered BIS acceptable for medical situations such as palliative sedation and pain assessment. Perceived effectiveness, ethicality, and usefulness considerations underpinned reasons and concerns around acceptability.

CONCLUSIONS

Potential end-users expressed diverse attitudes towards BIS monitoring in dementia end-of-life care. If BIS or similar technologies are to be implemented in the future, care must be taken to ensure that the device has sufficient added value, that the person with dementia and family are well informed, and that the technology does not replace human care. Future research should investigate its efficacy and feasibility in the situations that were deemed acceptable.

KETAMINE: Neural- and network-level changes

Ketamine is a widely used clinical drug that has several functional and clinical applications, including its use as an anaesthetic, analgesic, anti-depressive, anti-suicidal agent, among others. Among its diverse behavioral effects, it influences short-term memory and induces psychedelic effects. At the neural level across different brain areas, it modulates neural firing rates, neural tuning, brain oscillations, and modularity, while promoting hypersynchrony and random connectivity between neurons. In our recent studies we demonstrated that topical application of ketamine on the visual cortex alters neural tuning and promotes vigorous connectivity between neurons by decreasing their firing variability. Here, we begin with a brief review of the literature, followed by results from our lab, where we synthesize a dendritic model of neural tuning and network changes following ketamine application. This model has potential implications for focused modulation of cortical networks in clinical settings. Finally, we identify current gaps in research and suggest directions for future studies, particularly emphasizing the need for more animal experiments to establish a platform for effective translation and synergistic therapies combining ketamine with other protocols such as training and adaptation. In summary, investigating ketamine's broader systemic effects, not only provides deeper insight into cognitive functions and consciousness but also paves the way to advance therapies for neuropsychiatric disorders.

Electroencephalographic and Cardiovascular Assessments of Isoflurane-Anesthetized Dogs

This study investigated the use of frontal electroencephalography (EEG) to monitor varying levels of isoflurane anesthesia in dogs. The patient state index (PSI), burst suppression ratio (SR), and waveforms, were continuously recorded while mean arterial blood pressure (MBP), heart rate, responses to electric stimuli, and subjective anesthetic "depth" were assessed every 3 min. At deep anesthesia (2.5× MAC - 3.2%), the PSI (6.5 ± 10.8) and MBP (45.6 ± 16.4 mmHg) were the lowest, and SR was the highest (78.3 ± 24.0%). At 1× MAC (1.3%), the PSI and MBP increased significantly to 47.8 ± 12.6 and 99.8 ± 13.2, respectively, and SR decreased to 0.5 ± 2.5%. The EEG was predominantly isoelectric at 2×-2.5× MAC, indicating unconsciousness and unresponsiveness. As anesthesia lightened, waveforms transitioned to flatter and faster activity patterns with a response to noxious stimuli, suggesting regained consciousness. The PSI and MBP exhibited a stronger correlation (ρ = 0.8098, p = 0.001) than the relationship of PSI with heart rate (ρ = -0.2089, p = 0.249). Five of the six dogs experienced rough recovery, possibly due to high SR and low MBP. These findings suggest that EEG monitoring in dogs can be a valuable tool for the real-time tracking of brain states and can be used to guide the management of isoflurane anesthesia.

Changes in Intrinsic Connectivity Networks Topology Across Levels of Dexmedetomidine-Induced Alteration of Consciousness

BACKGROUND

Human consciousness is generally thought to emerge from the activity of intrinsic connectivity networks (resting-state networks [RSNs]) of the brain, which have topological characteristics including, among others, graph strength and efficiency. So far, most functional brain imaging studies in anesthetized subjects have compared wakefulness and unresponsiveness, a state considered as corresponding to unconsciousness. Sedation and general anesthesia not only produce unconsciousness but also phenomenological states of preserved mental content and perception of the environment (connected consciousness), and preserved mental content but no perception of the environment (disconnected consciousness). Unresponsiveness may be seen during unconsciousness, but also during disconnectedness. Deep dexmedetomidine sedation is frequently a state of disconnected consciousness. In this study, we were interested in characterizing the RSN topology changes across 4 different and steady-state levels of dexmedetomidine-induced alteration of consciousness, namely baseline (Awake, drug-free state), Mild sedation (drowsy, still responding), Deep sedation (unresponsive), and Recovery, with a focus on changes occurring between a connected consciousness state and an unresponsiveness state.

METHODS

A functional magnetic resonance imaging database acquired in 14 healthy volunteers receiving dexmedetomidine sedation was analyzed using a method combining independent component analysis and graph theory, specifically looking at changes in connectivity strength and efficiency occurring during the 4 above-mentioned dexmedetomidine-induced altered consciousness states.

RESULTS

Dexmedetomidine sedation preserves RSN architecture. Unresponsiveness during dexmedetomidine sedation is mainly characterized by a between-networks graph strength alteration and within-network efficiency alteration of lower-order sensory RSNs, while graph strength and efficiency in higher-order RSNs are relatively preserved.

CONCLUSIONS

The differential dexmedetomidine-induced RSN topological changes evidenced in this study may be the signature of inadequate processing of sensory information by lower-order RSNs, and of altered communication between lower-order and higher-order networks, while the latter remain functional. If replicated in an experimental paradigm distinguishing, in unresponsive subjects, disconnected consciousness from unconsciousness, such changes would sustain the hypothesis that disconnected consciousness arises from altered information handling by lower-order sensory networks and altered communication between lower-order and higher-order networks, while the preservation of higher-order networks functioning allows for an internally generated mental content (or dream).

Does Cognitive Load Affect Measures of Consciousness?

BACKGROUND

Developing and testing methods for reliably measuring the state of consciousness of individuals is important for both basic research and clinical purposes. In recent years, several promising measures of consciousness, grounded in theoretical developments, have been proposed. However, the degrees to which these measures are affected by changes in brain activity that are not related to changes in the degree of consciousness has not been well tested. In this study, we examined whether several of these measures are modulated by the loading of cognitive resources.

METHODS

We recorded electroencephalography (EEG) from 12 participants in two conditions: (1) while passively attending to sensory stimuli related to the measures and (2) during increased cognitive load consisting of a demanding working memory task. We investigated whether a set of proposed objective EEG-based measures of consciousness differed between the passive and the cognitively demanding conditions.

RESULTS

The P300b event-related potential (sensitive to conscious awareness of deviance from an expected pattern in auditory stimuli) was significantly affected by concurrent performance on a working memory task, whereas various measures based on signal diversity of spontaneous and perturbed EEG were not.

CONCLUSION

Because signal diversity-based measures of spontaneous or perturbed EEG are not sensitive to the degree of cognitive load, we suggest that these measures may be used in clinical situations where attention, sensory processing, or command following might be impaired.

Propofol disrupts the functional core-matrix architecture of the thalamus in humans

Research into the role of thalamocortical circuits in anesthesia-induced unconsciousness is difficult due to anatomical and functional complexity. Prior neuroimaging studies have examined either the thalamus as a whole or focused on specific subregions, overlooking the distinct neuronal subtypes like core and matrix cells. We conducted a study of heathy volunteers and functional magnetic resonance imaging during conscious baseline, deep sedation, and recovery. We advanced the functional gradient mapping technique to delineate the functional geometry of thalamocortical circuits, within a framework of the unimodal-transmodal functional axis of the cortex. Here we show a significant shift in this geometry during deep sedation, marked by a transmodal-deficient geometry. This alteration is closely linked to the spatial variations in the matrix cell composition within the thalamus. This research bridges cellular and systems-level understanding, highlighting the crucial role of thalamic core-matrix functional architecture in understanding the neural mechanisms of states of consciousness.

EEG signature of near-death-like experiences during syncope-induced periods of unresponsiveness

During fainting, disconnected consciousness may emerge in the form of dream-like experiences. Characterized by extra-ordinary and mystical features, these subjective experiences have been associated to near-death-like experiences (NDEs-like). We here aim to assess brain activity during syncope-induced disconnected consciousness by means of high-density EEG monitoring. Transient loss of consciousness and unresponsiveness were induced in 27 healthy volunteers through hyperventilation, orthostasis, and Valsalva maneuvers. Upon awakening, subjects were asked to report memories, if any. The Greyson NDE scale was used to evaluate the potential phenomenological content experienced during the syncope-induced periods of unresponsiveness. EEG source reconstruction assessed cortical activations during fainting, which were regressed out with subjective reports collected upon recovery of normal consciousness. We also conducted functional connectivity, graph-theoretic and complexity analyses. High quality high-density EEG data were obtained in 22 volunteers during syncope and unresponsiveness (lasting 22±8 s). NDE-like features (Greyson NDE scale total score ≥7/32) were apparent for eight volunteers and characterized by higher activity in delta, theta and beta2 bands in temporal and frontal regions. The richness of the NDE-like content was associated with delta, theta and beta2 bands cortical current densities, in temporal, parietal and frontal lobes, including insula, right temporoparietal junction, and cingulate cortex. Our analyses also revealed a higher complexity and that networks related to delta, theta, and beta2 bands were characterized by a higher overall connectivity paralleled by a higher segregation (i.e., local efficiency) and a higher integration (i.e., global efficiency) for the NDE-like group compared to the non-NDE-like group. Fainting-induced NDE-like episodes seem to be sustained by surges of neural activity representing promising markers of disconnected consciousness.

Critical dynamics in spontaneous EEG predict anesthetic-induced loss of consciousness and perturbational complexity

Consciousness has been proposed to be supported by electrophysiological patterns poised at criticality, a dynamical regime which exhibits adaptive computational properties, maximally complex patterns and divergent sensitivity to perturbation. Here, we investigate dynamical properties of the resting-state electroencephalogram (EEG) of healthy subjects undergoing general anesthesia with propofol, xenon or ketamine. Importantly, all participants were unresponsive under anesthesia, while consciousness was retained only during ketamine anesthesia (in the form of vivid dreams), enabling an experimental dissociation between unresponsiveness and unconsciousness. For each condition, we measure (i) avalanche criticality, (ii) chaoticity, and (iii) criticality-related metrics, revealing that states of unconsciousness are characterized by a distancing from both avalanche criticality and the edge of chaos. We then ask whether these same dynamical properties are predictive of the perturbational complexity index (PCI), a TMS-based measure that has shown remarkably high sensitivity in detecting consciousness independently of behavior. We successfully predict individual subjects' PCI values with considerably high accuracy from resting-state EEG dynamical properties alone. Our results establish a firm link between perturbational complexity and criticality, and provide further evidence that criticality is a necessary condition for the emergence of consciousness.

Content-state dimensions characterize different types of neuronal markers of consciousness

Identifying the neuronal markers of consciousness is key to supporting the different scientific theories of consciousness. Neuronal markers of consciousness can be defined to reflect either the brain signatures underlying specific conscious content or those supporting different states of consciousness, two aspects traditionally studied separately. In this paper, we introduce a framework to characterize markers according to their dynamics in both the "state" and "content" dimensions. The 2D space is defined by the marker's capacity to distinguish the conscious states from non-conscious states (on the x-axis) and the content (e.g. perceived versus unperceived or different levels of cognitive processing on the y-axis). According to the sign of the x- and y-axis, markers are separated into four quadrants in terms of how they distinguish the state and content dimensions. We implement the framework using three types of electroencephalography markers: markers of connectivity, markers of complexity, and spectral summaries. The neuronal markers of state are represented by the level of consciousness in (i) healthy participants during a nap and (ii) patients with disorders of consciousness. On the other hand, the neuronal markers of content are represented by (i) the conscious content in healthy participants' perception task using a visual awareness paradigm and (ii) conscious processing of hierarchical regularities using an auditory local-global paradigm. In both cases, we see separate clusters of markers with correlated and anticorrelated dynamics, shedding light on the complex relationship between the state and content of consciousness and emphasizing the importance of considering them simultaneously. This work presents an innovative framework for studying consciousness by examining neuronal markers in a 2D space, providing a valuable resource for future research, with potential applications using diverse experimental paradigms, neural recording techniques, and modeling investigations.

Unravelling consciousness and brain function through the lens of time, space, and information

Disentangling how cognitive functions emerge from the interplay of brain dynamics and network architecture is among the major challenges that neuroscientists face. Pharmacological and pathological perturbations of consciousness provide a lens to investigate these complex challenges. Here, we review how recent advances about consciousness and the brain's functional organisation have been driven by a common denominator: decomposing brain function into fundamental constituents of time, space, and information. Whereas unconsciousness increases structure-function coupling across scales, psychedelics may decouple brain function from structure. Convergent effects also emerge: anaesthetics, psychedelics, and disorders of consciousness can exhibit similar reconfigurations of the brain's unimodal-transmodal functional axis. Decomposition approaches reveal the potential to translate discoveries across species, with computational modelling providing a path towards mechanistic integration.

Behavioral and cortical arousal from sleep, muscimol-induced coma, and anesthesia by direct optogenetic stimulation of cortical neurons

The cerebral cortex is widely considered part of the neural substrate of consciousness, but direct causal evidence is missing. Here, we tested in mice whether optogenetic activation of cortical neurons in posterior parietal cortex (PtA) or medial prefrontal cortex (mPFC) is sufficient for arousal from three behavioral states characterized by progressively deeper unresponsiveness: sleep, a coma-like state induced by muscimol injection in the midbrain, and deep sevoflurane-dexmedetomidine anesthesia. We find that cortical stimulation always awakens the mice from both NREM sleep and REM sleep, with PtA requiring weaker/shorter light pulses than mPFC. Moreover, in most cases light pulses produce both cortical activation (decrease in low frequencies) and behavioral arousal (recovery of the righting reflex) from brainstem coma, as well as cortical activation from anesthesia. These findings provide evidence that direct activation of cortical neurons is sufficient for behavioral and/or cortical arousal from sleep, brainstem coma, and anesthesia.

Touching the unconscious in the unconscious - hypnotic communication with unconscious patients

If hypnosis means contact to the unconscious to modulate psychological and physiological functions by means of suggestions, and if this is facilitated by attenuation of the critical mind, then the question arises as to whether suggestions also have an effect when waking consciousness is otherwise eliminated, namely by coma or anesthesia. A prerequisite would be perception, which actually is evidenced by reports of patients after traumatic brain injury, artificial coma, resuscitation or general anesthesia. Moreover, posttraumatic stress disorder (PTSD) frequently observed after these medical situations is hardly explainable without some sort of awareness under such conditions. Even advanced neurophysiological diagnostic cannot yet rule out consciousness or sensory processing. Especially reference to perception during unconsciousness is given by the results of a recent multicenter study on the effects of hypnotic communication with patients under controlled adequate deep general anesthesia. The observed reductions in incidence and severity of postoperative pain, opioid use, nausea and vomiting cannot be explained by the reaction of a few but only by a considerable proportion of patients. This leads to a strong plea for a more careful treatment of unconscious patients in the emergency room, operating theater or intensive care unit, for the abandonment of the restriction of therapeutic communication to awake patients, and for new aspects of communication and hypnosis research. Obviously, loss of consciousness does not protect against psychological injury, and continuation of communication is needed. But how and what to talk to unconscious patients? Generally addressing the unconscious mind with suggestions that generally exert their effects unconsciously, hypnotic communication appears to be the adequate language. Especially addressing meaningful topics, as derived from the basic psychological needs and known stressors, appears essential. With respect to negative effects by negative or missing communication or to the proposed protective and supporting effects of therapeutic communication with patients clinically rated as unconscious, the role of consciousness is secondary. For the effects of perceived signals and suggestions it does not matter whether consciousness is absent, or partial, or unrecognized present.

Substance-dependent EEG during recovery from anesthesia and optimization of monitoring

The electroencephalographic (EEG) activity during anesthesia emergence contains information about the risk for a patient to experience postoperative delirium, but the EEG dynamics during emergence challenge monitoring approaches. Substance-specific emergence characteristics may additionally limit the reliability of commonly used processed EEG indices during emergence. This study aims to analyze the dynamics of different EEG indices during anesthesia emergence that was maintained with different anesthetic regimens. We used the EEG of 45 patients under general anesthesia from the emergence period. Fifteen patients per group received sevoflurane, isoflurane (+ sufentanil) or propofol (+ remifentanil) anesthesia. One channel EEG and the bispectral index (BIS A-1000) were recorded during the study. We replayed the EEG back to the Conox, Entropy Module, and the BIS Vista to evaluate and compare the index behavior. The volatile anesthetics induced significantly higher EEG frequencies, causing higher indices (AUC > 0.7) over most parts of emergence compared to propofol. The median duration of "awake" indices (i.e., > 80) before the return of responsiveness (RoR) was significantly longer for the volatile anesthetics (p < 0.001). The different indices correlated well under volatile anesthesia (rs > 0.6), with SE having the weakest correlation. For propofol, the correlation was lower (rs < 0.6). SE was significantly higher than BIS and, under propofol anesthesia, qCON. Systematic differences of EEG-based indices depend on the drugs and devices used. Thus, to avoid early awareness or anesthesia overdose using an EEG-based index during emergence, the anesthetic regimen, the monitor used, and the raw EEG trace should be considered for interpretation before making clinical decisions.

A measure centrality index for systematic empirical comparison of consciousness theories

Consciousness science is marred by disparate constructs and methodologies, making it challenging to systematically compare theories. This foundational crisis casts doubts on the scientific character of the field itself. Addressing it, we propose a framework for systematically comparing consciousness theories by introducing a novel inter-theory classification interface, the Measure Centrality Index (MCI). Recognizing its gradient distribution, the MCI assesses the degree of importance a specific empirical measure has for a given consciousness theory. We apply the MCI to probe how the empirical measures of the Global Neuronal Workspace Theory (GNW), Integrated Information Theory (IIT), and Temporospatial Theory of Consciousness (TTC) would fare within the context of the other two. We demonstrate that direct comparison of IIT, GNW, and TTC is meaningful and valid for some measures like Lempel-Ziv Complexity (LZC), Autocorrelation Window (ACW), and possibly Mutual Information (MI). In contrast, it is problematic for others like the anatomical and physiological neural correlates of consciousness (NCC) due to their MCI-based differential weightings within the structure of the theories. In sum, we introduce and provide proof-of-principle of a novel systematic method for direct inter-theory empirical comparisons, thereby addressing isolated evolution of theories and confirmatory bias issues in the state-of-the-art neuroscience of consciousness.

Anesthesia and the neurobiology of consciousness

In 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 of 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 the data derived from the anesthetized state for the science of consciousness and then conclude with outstanding questions, reflections, and future directions.

An integrative, multiscale view on neural theories of consciousness

How is conscious experience related to material brain processes? A variety of theories aiming to answer this age-old question have emerged from the recent surge in consciousness research, and some are now hotly debated. Although most researchers have so far focused on the development and validation of their preferred theory in relative isolation, this article, written by a group of scientists representing different theories, takes an alternative approach. Noting that various theories often try to explain different aspects or mechanistic levels of consciousness, we argue that the theories do not necessarily contradict each other. Instead, several of them may converge on fundamental neuronal mechanisms and be partly compatible and complementary, so that multiple theories can simultaneously contribute to our understanding. Here, we consider unifying, integration-oriented approaches that have so far been largely neglected, seeking to combine valuable elements from various theories.

Neurobiological basis of emergence from anesthesia

The suppression of consciousness by anesthetics and the emergence of the brain from anesthesia are complex and elusive processes. Anesthetics may exert their inhibitory effects by binding to specific protein targets or through membrane-mediated targets, disrupting neural activity and the integrity and function of neural circuits responsible for signal transmission and conscious perception/subjective experience. Emergence from anesthesia was generally thought to depend on the elimination of the anesthetic from the body. Recently, studies have suggested that emergence from anesthesia is a dynamic and active process that can be partially controlled and is independent of the specific molecular targets of anesthetics. This article summarizes the fundamentals of anesthetics' actions in the brain and the mechanisms of emergence from anesthesia that have been recently revealed in animal studies.

Tests for consciousness in humans and beyond

Which systems/organisms are conscious? New tests for consciousness ('C-tests') are urgently needed. There is persisting 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 and rapid developments in artificial intelligence (AI), neural organoids, and xenobot technology. Although a number of C-tests have been proposed in recent years, most are of limited use, and currently we have no C-tests for many of the populations for which they are most critical. Here, we identify challenges facing any attempt to develop C-tests, propose a multidimensional classification of such tests, and identify strategies that might be used to validate them.

Local orchestration of distributed functional patterns supporting loss and restoration of consciousness in the primate brain

A central challenge of neuroscience is to elucidate how brain function supports consciousness. Here, we combine the specificity of focal deep brain stimulation with fMRI coverage of the entire cortex, in awake and anaesthetised non-human primates. During propofol, sevoflurane, or ketamine anaesthesia, and subsequent restoration of responsiveness by electrical stimulation of the central thalamus, we investigate how loss of consciousness impacts distributed patterns of structure-function organisation across scales. We report that distributed brain activity under anaesthesia is increasingly constrained by brain structure across scales, coinciding with anaesthetic-induced collapse of multiple dimensions of hierarchical cortical organisation. These distributed signatures are observed across different anaesthetics, and they are reversed by electrical stimulation of the central thalamus, coinciding with recovery of behavioural markers of arousal. No such effects were observed upon stimulating the ventral lateral thalamus, demonstrating specificity. Overall, we identify consistent distributed signatures of consciousness that are orchestrated by specific thalamic nuclei.

Changes in information integration and brain networks during propofol-, dexmedetomidine-, and ketamine-induced unresponsiveness

BACKGROUND

Information integration and network science are important theories for quantifying consciousness. However, whether these theories propose drug- or conscious state-related changes in EEG during anaesthesia-induced unresponsiveness remains unknown.

METHODS

A total of 72 participants were randomised to receive i.v. infusion of propofol, dexmedetomidine, or ketamine at a constant infusion rate until loss of responsiveness. High-density EEG was recorded during the consciousness transition from the eye-closed baseline to the unresponsiveness state and then to the recovery of the responsiveness state. Permutation cross mutual information (PCMI) and PCMI-based brain networks in broadband (0.1-45 Hz) and sub-band frequencies were used to analyse drug- and state-related EEG signature changes.

RESULTS

PCMI and brain networks exhibited state-related changes in certain brain regions and frequency bands. The within-area PCMI of the frontal, parietal, and occipital regions, and the between-area PCMI of the parietal-occipital region (median [inter-quartile ranges]), baseline vs unresponsive were as follows: 0.54 (0.46-0.58) vs 0.46 (0.40-0.50), 0.58 (0.52-0.60) vs 0.48 (0.44-0.53), 0.54 (0.49-0.59) vs 0.47 (0.42-0.52) decreased during anaesthesia for three drugs (P<0.05). Alpha PCMI in the frontal region, and gamma PCMI in the posterior area significantly decreased in the unresponsive state (P<0.05). The frontal, parietal, and occipital nodal clustering coefficients and parietal nodal efficiency decreased in the unresponsive state (P<0.05). The increased normalised path length in delta, theta, and gamma bands indicated impaired global integration (P<0.05).

CONCLUSIONS

The three anaesthetics caused changes in information integration patterns and network functions. Thus, it is possible to build a quantifying framework for anaesthesia-induced conscious state changes on the EEG scale using PCMI and network science.

Study protocol: Cerebral characterization of sensory gating in disconnected dreaming states during propofol anesthesia using fMRI

Background

Disconnected consciousness describes a state in which subjective experience (i.e., consciousness) becomes isolated from the external world. It appears frequently during sleep or sedation, when subjective experiences remain vivid but are unaffected by external stimuli. Traditional methods of differentiating connected and disconnected consciousness, such as relying on behavioral responsiveness or on post-anesthesia reports, have demonstrated limited accuracy: unresponsiveness has been shown to not necessarily equate to unconsciousness and amnesic effects of anesthesia and sleep can impair explicit recollection of events occurred during sleep/sedation. Due to these methodological challenges, our understanding of the neural mechanisms underlying sensory disconnection remains limited.

Methods

To overcome these methodological challenges, we employ a distinctive strategy by combining a serial awakening paradigm with auditory stimulation during mild propofol sedation. While under sedation, participants are systematically exposed to auditory stimuli and questioned about their subjective experience (to assess consciousness) and their awareness of the sounds (to evaluate connectedness/disconnectedness from the environment). The data collected through interviews are used to categorize participants into connected and disconnected consciousness states. This method circumvents the requirement for responsiveness in assessing consciousness and mitigates amnesic effects of anesthesia as participants are questioned while still under sedation. Functional MRI data are concurrently collected to investigate cerebral activity patterns during connected and disconnected states, to elucidate sensory disconnection neural gating mechanisms. We examine whether this gating mechanism resides at the thalamic level or results from disruptions in information propagation to higher cortices. Furthermore, we explore the potential role of slow-wave activity (SWA) in inducing disconnected consciousness by quantifying high-frequency BOLD oscillations, a known correlate of slow-wave activity.

Discussion

This study represents a notable advancement in the investigation of sensory disconnection. The serial awakening paradigm effectively mitigates amnesic effects by collecting reports immediately after regaining responsiveness, while still under sedation. Ultimately, this research holds the potential to understand how sensory gating is achieved at the neural level. These biomarkers might be relevant for the development of sensitive anesthesia monitoring to avoid intraoperative connected consciousness and for the assessment of patients suffering from pathologically reduced consciousness.

Clinical trial registration

European Union Drug Regulating Authorities Clinical Trials Database (EudraCT), identifier 2020-003524-17.

Depth of Anesthesia and Nociception Monitoring: Current State and Vision For 2050

Anesthesia objectives have evolved into combining hypnosis, amnesia, analgesia, paralysis, and suppression of the sympathetic autonomic nervous system. Technological improvements have led to new monitoring strategies, aimed at translating a qualitative physiological state into quantitative metrics, but the optimal strategies for depth of anesthesia (DoA) and analgesia monitoring continue to stimulate debate. Historically, DoA monitoring used patient's movement as a surrogate of awareness. Pharmacokinetic models and metrics, including minimum alveolar concentration for inhaled anesthetics and target-controlled infusion models for intravenous anesthesia, provided further insights to clinicians, but electroencephalography and its derivatives (processed EEG; pEEG) offer the potential for personalization of anesthesia care. Current studies appear to affirm that pEEG monitoring decreases the quantity of anesthetics administered, diminishes postanesthesia care unit duration, and may reduce the occurrence of postoperative delirium (notwithstanding the difficulties of defining this condition). Major trials are underway to further elucidate the impact on postoperative cognitive dysfunction. In this manuscript, we discuss the Bispectral (BIS) index, Narcotrend monitor, Patient State Index, entropy-based monitoring, and Neurosense monitor, as well as middle latency evoked auditory potential, before exploring how these technologies could evolve in the upcoming years. In contrast to developments in pEEG monitors, nociception monitors remain by comparison underdeveloped and underutilized. Just as with anesthetic agents, excessive analgesia can lead to harmful side effects, whereas inadequate analgesia is associated with increased stress response, poorer hemodynamic conditions and coagulation, metabolic, and immune system dysregulation. Broadly, 3 distinct monitoring strategies have emerged: motor reflex, central nervous system, and autonomic nervous system monitoring. Generally, nociceptive monitors outperform basic clinical vital sign monitoring in reducing perioperative opioid use. This manuscript describes pupillometry, surgical pleth index, analgesia nociception index, and nociception level index, and suggest how future developments could impact their use. The final section of this review explores the profound implications of future monitoring technologies on anesthesiology practice and envisages 3 transformative scenarios: helping in creation of an optimal analgesic drug, the advent of bidirectional neuron-microelectronic interfaces, and the synergistic combination of hypnosis and virtual reality.

Separation of responsive and unresponsive patients under clinical conditions: comparison of symbolic transfer entropy and permutation entropy

Electroencephalogram (EEG)-based monitoring during general anesthesia may help prevent harmful effects of high or low doses of general anesthetics. There is currently no convincing evidence in this regard for the proprietary algorithms of commercially available monitors. The purpose of this study was to investigate whether a more mechanism-based parameter of EEG analysis (symbolic transfer entropy, STE) can separate responsive from unresponsive patients better than a strictly probabilistic parameter (permutation entropy, PE) under clinical conditions. In this prospective single-center study, the EEG of 60 surgical ASA I-III patients was recorded perioperatively. During induction of and emergence from anesthesia, patients were asked to squeeze the investigators' hand every 15s. Time of loss of responsiveness (LoR) during induction and return of responsiveness (RoR) during emergence from anesthesia were registered. PE and STE were calculated at -15s and +30s of LoR and RoR and their ability to separate responsive from unresponsive patients was evaluated using accuracy statistics. 56 patients were included in the final analysis. STE and PE values decreased during anesthesia induction and increased during emergence. Intra-individual consistency was higher during induction than during emergence. Accuracy values during LoR and RoR were 0.71 (0.62-0.79) and 0.60 (0.51-0.69), respectively for STE and 0.74 (0.66-0.82) and 0.62 (0.53-0.71), respectively for PE. For the combination of LoR and RoR, values were 0.65 (0.59-0.71) for STE and 0.68 (0.62-0.74) for PE. The ability to differentiate between the clinical status of (un)responsiveness did not significantly differ between STE and PE at any time. Mechanism-based EEG analysis did not improve differentiation of responsive from unresponsive patients compared to the probabilistic PE.Trial registration: German Clinical Trials Register ID: DRKS00030562, November 4, 2022, retrospectively registered.

Evaluation of putative signatures of consciousness using specific definitions of responsiveness, connectedness, and consciousness

BACKGROUND

Understanding the neural correlates of consciousness has important ramifications for the theoretical understanding of consciousness and for clinical anaesthesia. A major limitation of prior studies is the use of responsiveness as an index of consciousness. We identified a collection of measures derived from unresponsive subjects and more specifically their association with consciousness (any subjective experience) or connectedness (specific experience of environmental stimuli).

METHODS

Using published data generated through the UNderstanding Consciousness Connectedness and Intra-Operative Unresponsiveness Study (NCT03284307), we evaluated 10 previously published resting-state EEG-based measures that were derived using unresponsiveness as a proxy for unconsciousness. Measures were tested across dexmedetomidine and propofol sedation and natural sleep. These markers represent the complexity, connectivity, cross-frequency coupling, graph theory, and power spectrum measures.

RESULTS

Although many of the proposed markers were associated with consciousness per se (reported subjective experience), none were specific to consciousness alone; rather, each was also associated with connectedness (i.e. awareness of the environment). In addition, multiple markers showed no association with consciousness and were associated only with connectedness. Of the markers tested, loss of normalised-symbolic transfer entropy (front to back) was associated with connectedness across all three experimental conditions, whereas the transition from disconnected consciousness to unconsciousness was associated with significant decreases in permutation entropy and spectral exponent (P<0.05 for all conditions).

CONCLUSIONS

None of the proposed EEG-based neural correlates of unresponsiveness corresponded solely to consciousness, highlighting the need for a more conservative use of the term (un)consciousness when assessing unresponsive participants.

CLINICAL TRIAL REGISTRATION

NCT03284307.

Consciousness and General Anesthesia: Challenges for Measuring the Depth of Anesthesia

The optimal consciousness level required for general anesthesia with surgery is unclear, but in existing practice, anesthetic oblivion, may be incomplete. This article discusses the concept of consciousness, how it is altered by anesthetics, the challenges for assessing consciousness, currently used technologies for assessing anesthesia levels, and future research directions. Wakefulness is marked by a subjective experience of existence (consciousness), perception of input from the body or the environment (connectedness), the ability for volitional responsiveness, and a sense of continuity in time. Anesthetic drugs may selectively impair some of these components without complete extinction of the subjective experience of existence. In agreement with Sanders et al. (2012), the authors propose that a state of disconnected consciousness is the optimal level of anesthesia, as it likely avoids both awareness and the possible dangers of oversedation. However, at present, there are no reliably tested indices that can discriminate between connected consciousness, disconnected consciousness, and complete unconsciousness.

Propofol Disrupts the Functional Core-Matrix Architecture of the Thalamus in Humans

Research into the role of thalamocortical circuits in anesthesia-induced unconsciousness is difficult due to anatomical and functional complexity. Prior neuroimaging studies have examined either the thalamus as a whole or focused on specific subregions, overlooking the distinct neuronal subtypes like core and matrix cells. We conducted a study of heathy volunteers and functional magnetic resonance imaging during conscious baseline, deep sedation, and recovery. We advanced the functional gradient mapping technique to delineate the functional geometry of thalamocortical circuits, within a framework of the unimodal-transmodal functional axis of the cortex. We observed a significant shift in this geometry during unconsciousness, marked by the dominance of unimodal over transmodal geometry. This alteration was closely linked to the spatial variations in the density of matrix cells within the thalamus. This research bridges cellular and systems-level understanding, highlighting the crucial role of thalamic core-matrix functional architecture in understanding the neural mechanisms of states of consciousness.

Chinese translation and validation of the Near-Death Experience Content scale

Introduction

In recent years, a growing number of near-death experience (NDE) testimonies have been collected worldwide due to an increasing interest in research on this phenomenon. China has many patients who survive life-threatening situations, leaving over much data on NDEs to be collected for research. In the historical context of Eastern civilization, many mentally controlled practices in China can also lead to "NDEs-like" (e.g., meditation). This study aimed (1) to translate and validate the recently developed Near-Death Experience Content (NDE-C) scale into Chinese and (2) to quantify and identify NDEs and NDEs-like in China with this new Chinese version of the NDE-C scale.

Methods

Here, we presented the work that had been performed to translate the NDE-C scale into Chinese and validated this version on 79 NDE testimonies.

Results

Brislin's back-translation model was performed to translate a Chinese version of the NDE-C scale and internal consistency (the Cronbach's α value for the total group = 0.846) as well as the confirmatory factor analysis was conducted.

Discussion

Currently, the Chinese version of the NDE-C scale is ready for use in research practice in the context of Eastern culture, to screen people who have experienced an NDEs(-like) and to quantify their subjective experience, promoting further NDEs-related research in China.

EEG spectral slope: A reliable indicator for continuous evaluation of consciousness levels during propofol anesthesia

The level of consciousness undergoes continuous alterations during anesthesia. Prior to the onset of propofol-induced complete unconsciousness, degraded levels of behavioral responsiveness can be observed. However, a reliable index to monitor altered consciousness levels during anesthesia has not been sufficiently investigated. In this study, we obtained 60-channel EEG data from 24 healthy participants during an ultra-slow propofol infusion protocol starting with an initial concentration of 1 μg/ml and a stepwise increase of 0.2 μg/ml in concentration. Consecutive auditory stimuli were delivered every 5 to 6 s, and the response time to the stimuli was used to assess the responsiveness levels. We calculated the spectral slope in a time-resolved manner by extracting 5-second EEG segments at each auditory stimulus and estimated their correlation with the corresponding response time. Our results demonstrated that during slow propofol infusion, the response time to external stimuli increased, while the EEG spectral slope, fitted at 15-45 Hz, became steeper, and a significant negative correlation was observed between them. Moreover, the spectral slope further steepened at deeper anesthetic levels and became flatter during anesthesia recovery. We verified these findings using an external dataset. Additionally, we found that the spectral slope of frontal electrodes over the prefrontal lobe had the best performance in predicting the response time. Overall, this study used a time-resolved analysis to suggest that the EEG spectral slope could reliably track continuously altered consciousness levels during propofol anesthesia. Furthermore, the frontal spectral slope may be a promising index for clinical monitoring of anesthesia depth.

The nature of consciousness in anaesthesia

Neuroscientists agree on the value of locating the source of consciousness within the brain. Anaesthesiologists are no exception, and have their own operational definition of consciousness based on phenomenological observations during anaesthesia. The full functional correlates of consciousness are yet to be precisely identified, however rapidly evolving progress in this scientific domain has yielded several theories that attempt to model the generation of consciousness. They have received variable support from experimental observations, including those involving anaesthesia and its ability to reversibly modulate different aspects of consciousness. Aside from the interest in a better understanding of the mechanisms of consciousness, exploring the functional tenets of the phenomenological consciousness states of general anaesthesia has the potential to ultimately improve patient management. It could facilitate the design of specific monitoring devices and approaches, aiming at reliably detecting each of the possible states of consciousness during an anaesthetic procedure, including total absence of mental content (unconsciousness), and internal awareness (sensation of self and internal thoughts) with or without conscious perception of the environment (connected or disconnected consciousness, respectively). Indeed, it must be noted that unresponsiveness is not sufficient to infer absence of connectedness or even absence of consciousness. This narrative review presents the current knowledge in this field from a system-level, underlining the contribution of anaesthesia studies in supporting theories of consciousness, and proposing directions for future research.

Analgesia for the Bayesian Brain: How Predictive Coding Offers Insights Into the Subjectivity of Pain

PURPOSE OF REVIEW

In order to better treat pain, we must understand its architecture and pathways. Many modulatory approaches of pain management strategies are only poorly understood. This review aims to provide a theoretical framework of pain perception and modulation in order to assist in clinical understanding and research of analgesia and anesthesia.

RECENT FINDINGS

Limitations of traditional models for pain have driven the application of new data analysis models. The Bayesian principle of predictive coding has found increasing application in neuroscientific research, providing a promising theoretical background for the principles of consciousness and perception. It can be applied to the subjective perception of pain. Pain perception can be viewed as a continuous hierarchical process of bottom-up sensory inputs colliding with top-down modulations and prior experiences, involving multiple cortical and subcortical hubs of the pain matrix. Predictive coding provides a mathematical model for this interplay.

Criticality of resting-state EEG predicts perturbational complexity and level of consciousness during anesthesia

Consciousness has been proposed to be supported by electrophysiological patterns poised at criticality, a dynamical regime which exhibits adaptive computational properties, maximally complex patterns and divergent sensitivity to perturbation. Here, we investigated dynamical properties of the resting-state electroencephalogram of healthy subjects undergoing general anesthesia with propofol, xenon or ketamine. We then studied the relation of these dynamic properties with the perturbational complexity index (PCI), which has shown remarkably high sensitivity in detecting consciousness independent of behavior. All participants were unresponsive under anesthesia, while consciousness was retained only during ketamine anesthesia (in the form of vivid dreams)., enabling an experimental dissociation between unresponsiveness and unconsciousness. We estimated (i) avalanche criticality, (ii) chaoticity, and (iii) criticality-related measures, and found that states of unconsciousness were characterized by a distancing from both the edge of activity propagation and the edge of chaos. We were then able to predict individual subjects' PCI (i.e., PCImax) with a mean absolute error below 7%. Our results establish a firm link between the PCI and criticality and provide further evidence for the role of criticality in the emergence of consciousness.

Neuronal connected burst cascades bridge macroscale adaptive signatures across arousal states

The human brain displays a rich repertoire of states that emerge from the microscopic interactions of cortical and subcortical neurons. Difficulties inherent within large-scale simultaneous neuronal recording limit our ability to link biophysical processes at the microscale to emergent macroscopic brain states. Here we introduce a microscale biophysical network model of layer-5 pyramidal neurons that display graded coarse-sampled dynamics matching those observed in macroscale electrophysiological recordings from macaques and humans. We invert our model to identify the neuronal spike and burst dynamics that differentiate unconscious, dreaming, and awake arousal states and provide insights into their functional signatures. We further show that neuromodulatory arousal can mediate different modes of neuronal dynamics around a low-dimensional energy landscape, which in turn changes the response of the model to external stimuli. Our results highlight the promise of multiscale modelling to bridge theories of consciousness across spatiotemporal scales.

Theoretical Neurobiology of Consciousness Applied to Human Cerebral Organoids

Organoids and specifically human cerebral organoids (HCOs) are one of the most relevant novelties in the field of biomedical research. Grown either from embryonic or induced pluripotent stem cells, HCOs can be used as in vitro three-dimensional models, mimicking the developmental process and organization of the developing human brain. Based on that, and despite their current limitations, it cannot be assumed that they will never at any stage of development manifest some rudimentary form of consciousness. In the absence of behavioral indicators of consciousness, the theoretical neurobiology of consciousness being applied to unresponsive brain-injured patients can be considered with respect to HCOs. In clinical neurology, it is difficult to discern a capacity for consciousness in unresponsive brain-injured patients who provide no behavioral indicators of consciousness. In such scenarios, a validated neurobiological theory of consciousness, which tells us what the neural mechanisms of consciousness are, could be used to identify a capacity for consciousness. Like the unresponsive patients that provide a diagnostic difficulty for neurologists, HCOs provide no behavioral indicators of consciousness. Therefore, this article discusses how three prominent neurobiological theories of consciousness apply to human cerebral organoids. From the perspective of the Temporal Circuit Hypothesis, the Global Neuronal Workspace Theory, and the Integrated Information Theory, we discuss what neuronal structures and functions might indicate that cerebral organoids have a neurobiological capacity to be conscious.

Schnider and Eleveld Models for Propofol Target-Controlled Infusion Anesthesia: A Clinical Comparison

BACKGROUND

Various pharmacokinetic/pharmacodynamic (PK/PD) models have been developed to accurately dose propofol administration during total intravenous anesthesia with target-controlled infusion (TIVA-TCI). We aim to clinically compare the performance of the Schnider model and the new and general-purpose Eleveld PK/PD model during TIVA-TCI.

METHODS

We conducted a prospective observational study at a single center, enrolling 78 female patients, including 37 adults (aged < 65 years) and 41 elderly patients (aged ≥ 65 years). These patients underwent breast surgery with propofol-remifentanil TIVA-TCI guided by the bispectral index (BIS) for depth of anesthesia monitoring (target value 40-60) and the surgical plethysmographic index (SPI) for antinociception monitoring (target value 20-50) without neuromuscular blockade. The concentration at the effect site of propofol (CeP) at loss of responsiveness (LoR) during anesthesia maintenance (MA) and at return of responsiveness (RoR), the duration of surgery and anesthesia (min), the time to RoR (min), the propofol total dose (mg), the deepening of anesthesia events (DAEs), burst suppression events (BSEs), light anesthesia events (LAEs) and unwanted spontaneous responsiveness events (USREs) were considered to compare the two PK/PD models.

RESULTS

Patients undergoing BIS-SPI-guided TIVA-TCI with the Eleveld PK/PD model showed a lower CeP at LoR (1.7 (1.36-2.25) vs. 3.60 (3.00-4.18) μg/mL, p < 0.001), higher CePMA (2.80 (2.55-3.40) vs. 2.30 (1.80-2.50) μg/mL, p < 0.001) and at RoR (1.48 (1.08-1.80) vs. 0.64 (0.55-0.81) μg/mL, p < 0.001) than with the Schnider PK/PD model. Anesthetic hysteresis was observed only in the Schnider PK/PD model group (p < 0.001). DAEs (69.2% vs. 30.8%, p = 0.001) and BSEs (28.2% vs. 5.1%, p = 0.013) were more frequent with the Eleveld PK/PD model than with the Schnider PK/PD model in the general patient population. DAEs (63.2% vs. 27.3%, p = 0.030) and BSEs (31.6% vs. 4.5%, p = 0.036) were more frequent with the Eleveld PK/PD model than with the Schnider PK/PD model in the elderly.

CONCLUSIONS

The Schnider and Eleveld PK/PD models impact CePs differently. A greater incidence of DAEs and BSEs in the elderly suggests more attention is necessary in this group of patients undergoing BIS-SPI-guided TIVA-TCI with the Eleveld PK/PD than with the Schnider model.