Occasionally, during the stream of thought, people report experiencing no mental content or being unable to access any content, a mental state termed mind-blanking (MB). While MB appears to be a ubiquitous component of our mental lives, there is currently no systematic characterisation of how often MB occurs and under what conditions. The present preregistered systematic review and meta-analysis aimed to determine how often MB is reported in experience-sampling studies. Our search strategy yielded a sample of 59 studies, probing mental reports for more than 8500 participants. Using Bayesian linear modelling, we estimated the meta-analytic MB report rate at 10% of total experience sampling. We did not find any evidence for an effect of experience-sampling parameters on MB report rates. However, we identified that low arousal was associated with higher MB report frequency. Additionally, and contrary to the established literature, ADHD MB rates did not differ from our normative, baseline MB rate. Finally, using our meta-analytically derived posterior estimate, we simulated synthetic experience-sampling studies to determine appropriate sample sizes. In doing so, we provide heuristic sample-size recommendations to ensure high statistical power in prospective investigations. We recommend that prospective experience-sampling studies include 35 participants and 50 probes per participant, which should provide over 95% power to detect medium-sized effects. Overall, the present meta-analysis suggests that MB is fundamentally an infrequent mental state, yet its inclusion in experience-sampling paradigms provides accuracy and granularity into the full scope of mental states during spontaneous thinking.

Abstract Our responses to environmental inputs depend on the variations of our own physiological activity. However, the mechanisms by which the integration of sensory information with interoceptive signals shape bodily responses to external events remain debated. In this pre-registered study, we hypothesized three possible mechanisms underlying such exteroceptive-interoceptive integration: cardiac surprise, active inference, and dynamic coupling. To test them, we implemented a closed-loop stimulation procedure to play auditory deviations from sequences either synchronized or not with heartbeats which varied in type (omissions or rare tones) and predictability (random or regular intervals). First, we replicated previous findings that cardiac activity slows down in response to sound omissions only when sounds are synchronized with heartbeats. Second, we showed that this effect extends to rare tones, excluding the dynamic coupling hypothesis. Third, we demonstrated that these responses do not depend on the predictability of auditory deviations, excluding both cardiac surprise and active inference hypotheses. In a control experiment, we further observed that behavioral responses depend on the type and predictability of auditory deviants: participants can discriminate subjectively which sounds were synchronized with their own heartbeats without evidence of a relationship to interoception nor cardiac responses. Overall, these results demonstrate that auditory deviations slow down cardiac responses when locked to heartbeats but independently from their type and regularity, calling for novel hypotheses to account for the interoceptive-exteroceptive integration of sensory signals into cardiac activity. Impact statement Using a cardio-audio synchrony task, we show that cardiac responses slow down upon heartbeat-locked auditory deviations independently from their type or regularity, suggesting a simple, fundamental mechanism of integration of internal and external signals into bodily responses to the environment. The heart may provide a straightforward way to study basic self-related processes, without depending on behavior or self-report, which is especially valuable for individuals who are unable to respond or communicate.

Consciousness and cognition arise from the ongoing interactions between brain regions. Synchronous fluctuations of fMRI signals may indicate that two brain regions perform similar cognitive functions, but neural interactions are also constrained by anatomical connectivity and regions' molecular, cytoarchitectonic, and metabolic profiles. Here we disentangle the respective contributions of ongoing cognition and multimodal neurobiological constraints in shaping functional connectivity. We jointly contextualise haemodynamic FC against eight distinct multimodal representations of the human connectome: (i) structural connectivity from diffusion tractography; (ii) spatial embedding; (iii) similarity of transcriptional profiles from gene expression; (iv) similarity of receptor profiles from Positron Emission Tomography; (v) laminar profile similarity from histology; (vi) correlated electrophysiological activity from magnetoencephalography; (vii) correlated metabolic activity from PET glucose uptake; (viii) coordinated activation across 123 cognitive operations from the NeuroSynth meta-analytic engine. We demonstrate that cognitive co-activation is the dominant predictor of inter-regional fMRI synchrony in the awake human brain, even when quantified using intracranial electrical stimulation. Crucially, this predominance of cognitive co-activation for shaping functional connectivity is systematically obliterated across five datasets of pharmacological and pathological perturbations of consciousness (chronic disorders of consciousness; anaesthesia with sevoflurane, propofol, or ketamine) when cognition is disconnected from the environment or altogether abolished. Altogether, we show that multimodal predictors of functional architecture shift away from cognitive co-activation and toward anatomical-molecular constraints during pharmacological and pathological perturbations of consciousness.

In recent years, there has been a renewed interest in the conceptual and empirical study of altered states of consciousness (ASCs), induced pharmacologically or otherwise, driven by their potential clinical applications. To draw attention to the rich history of research in this domain, we review prominent classification schemes that have been proposed to introduce systematicity into the scientific study of ASCs. The reviewed ASC classification schemes fall into three groups according to the criteria they use for categorization: (1) based on the nature, variety, and intensity of subjective experiences (state-based), including conceptual descriptions and psychometric assessments, (2) based on the technique of induction (method-based), and (3) descriptions of neurophysiological mechanisms of ASCs (neuro/physio-based). By comparing and extending existing classification schemes, we can enhance efforts to identify neural correlates of consciousness, particularly when examining mechanisms of ASC induction and the resulting subjective experiences. Furthermore, an overview of what defining ASC characteristics different authors have proposed can inform future research in the conceptualization and quantification of ASC subjective effects, including the identification of those that might be relevant in clinical research. This review concludes by clustering the concepts from the state-based schemes, which are suggested for classifying ASC experiences. The resulting clusters can inspire future approaches to formulate and quantify the core phenomenology of ASC experiences to assist in basic and clinical research.

During wakefulness, the stream of thought is occasionally interrupted by moments when we cannot report any content, termed “mind blanking” (MB). As MB is a relatively unexplored mental state, we here examine how it relates to spontaneous thinking, namely thought content and thought dynamics. By reviewing empirical studies on the neural correlates of MB, we first indicate that MB reports are mediated by variations in cortical and physiological arousal levels. In terms of thought content, we propose to view MB on a dimensional space representing content types, where MB is unrelated to any type of content. In terms of thought dynamics, we suggest conceptualizing MB as a moment during content transitioning, or as a failure to transition across contents. Taken together, we suggest that MB has a unique place in the study of spontaneous thinking, and its inclusion can facilitate the isolation of the neural correlates of ongoing cognition.

Mind blanking (MB) is the inability to report mental events during unconstraint thinking. Previous work shows that MB is linked to decreased levels of cortical arousal, indicating dominance of cerebral mechanisms when reporting mental states. What remains inconclusive is whether MB can also ensue from autonomic arousal manipulations, pointing to the implication of peripheral physiology to mental events. Using experience sampling, neural, and physiological measurements in 26 participants, we first show that MB was reported more frequently in low arousal conditions, elicited by sleep deprivation. Also, there was partial evidence for a higher occurence of MB reports in high arousal conditions, elicited by intense physical exercise. Transition probabilities revealed that, after sleep deprivation, mind wandering was more likely to be followed by MB and less likely to be followed by more mind wandering reports. Using classification schemes, we found higher performance of a balanced random forest classifier trained on both neural and physiological markers in comparison to performance when solely neural or physiological were used. Collectively, we show that both cortical and autonomic arousal affect MB report occurrences. Our results establish that MB is supported by combined brain-body configurations, and, by linking mental and physiological states, they pave the way for novel embodied accounts of spontaneous thinking. ‘The stage 1 protocol for this Registered Report was accepted in principle on 02/01/23. The protocol, as accepted by the journal, can be found at: 10.17605/OSF.IO/SH2YE’ Techniques: Life sciences techniques, Biophysical methods [Electrocardiography - EKG]; Life sciences techniques, Biophysical methods [Electroencephalography - EEG]; CTS received date: 27.11.2024.

BACKGROUND:The impact of acute cannabis exposure on brain function and cognitive performance varies among individuals. Acute effects of cannabis on behavior may be absent or benign in chronic users, while occasional users experience significant impairment in day-to-day operations. It is hypothesized that repeated cannabis use induces neuroadaptations leading to tolerance and desensitization, although the precise mechanisms underlying these adaptations remain unclear. METHODS:In this study, we investigated acute and persistent effects of vaporized cannabis on brain dynamics in a placebo-controlled neuroimaging trial involving occasional (n = 23) and chronic (n = 20) cannabis users. Functional resting-state data were collected to assess dynamic functional connectivity changes during intoxication and their association with attentional performance and normative cannabinoid CB1 receptor density. RESULTS:Cannabis intoxication induced significant acute alterations in the dynamics of brain network organization, as shown by a reduced occurrence of a hyperconnected brain state in both user groups. Chronic users also displayed decreased segregation of brain networks independent of treatment condition, suggesting persisting neuroadaptations. Dynamic reconfiguration of hyperconnected brain motifs correlated with attentional performance, which was most impaired in occasional users, indicating tolerance in chronic users. Both the acute and persistent effects of cannabis on dynamic brain state organization were significantly associated with spatial CB1 receptor density. CONCLUSIONS:Acute cannabis-induced cognitive impairment is influenced by (persistent) network reconfigurations and CB1 receptor density. These findings emphasize the relevance of neural dynamics and individual neuroadaptations to (prolonged) cannabis use when assessing the behavioral effects of cannabis in therapeutic, legal, and societal settings.

During wakefulness, our thoughts transition between different contents. However, there are moments that are seemingly devoid of reportable content, referred to as mind blanking (MB). It remains unclear what these blanks represent, highlighting the definitional and phenomenological ambiguities surrounding MB. We map out MB in terms of its reportable expressions, neurophysiology, and relationship to adjacent phenomenology, including meditative practices and sleep. We propose a mechanistic account linking MB to changes at the physiological, neural, and cognitive levels. We suggest that ongoing experiences are characterized by degrees of richness, and that contentless events represent distinct mental states with their own diversity. We encourage future research to acknowledge MB as a reportable mental category, leading to a comprehensive understanding of ongoing experience.

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.

Mind blanking (MB) is a mental state of seemingly no reportable thought content. The question of how we can entertain no thoughts while awake is challenging for the study of spontaneous thinking. By combining EEG–fMRI with experience sampling during task performance, we categorised changes in mental content and self-reported vigilance to map the neurophysiological signatures of MB. We demonstrate that fMRI connectivity around MB reports is characterised by a “rich” pattern of long and short-range signal anticorrelations. At the same time, sleepiness reports are linked to a “simpler” hyperconnected fMRI pattern, characterised by overall positive connectivity. Put together, an interaction appears: when people report being alert, connectomes around MB reports resemble the hyperconnected pattern, indicating that the neuronal correlates of MB depend on self-rated vigilance. The hyperconnected pattern also correlated with EEG slow-wave activity, tying MB’s topology to sleep-like electrophysiology during wakefulness. Collectively, we show that distinct cortical events underlie the shared phenomenology of a thought-free mind. We conclude that MB’s neurophysiological correlates vary across perceived vigilance levels and that more refined characterisation of the neuronal correlates of thought-less mental states exist. Our findings build on the quest to bridge mental content and its absence with measurable brain activity and provide insights into how ongoing thinking is maintained during wakefulness. ### Competing Interest Statement The authors have declared no competing interest. Belgian Fund for Scientific Research (FRS-FNRS) European Union's Horizon 2020 Research and Innovation Marie Skłodowska-Curie RISE programme NeuronsXnets, 101007926 European Cooperation in Science and Technology COST Action, CA18106 Australian Research Council, DP240102680 National Health Medical Research Council, GNT1183280, GNT2037172 Japan Society for the Promotion of Science Grant-in-Aid for Transformative Research Areas, 23H04829, 23H04830 Japan Science and Technology (JST) Moonshot R&D Grant, JPMJMS2295-14 Theoretical Sciences Visiting Program, Okinawa Institute of Science and Technology

Consciousness research is commonly divided into two main areas: the study of states of consciousness and the study of contents of consciousness. States of consciousness refer to discrete modes of awareness elicited by normal states of the brain, such as those associated with wakefulness and sleep, and by abnormal factors, including brain lesions, pharmacological agents and other external interventions. Contents of consciousness refer what we are conscious of. In this chapter, we emphasize the dynamic nature of consciousness in terms of both its states and contents. First, we first observe that our life constantly alternates between different conscious and unconscious states, namely, sleep and wakefulness. Then, within each state, we note an inherent dynamism in content, with conscious experience ranging from content-full to content-less. By surveying the variety of conscious experiences across wakefulness and sleep, we highlight the similarities in reported contents across these states. We further discuss how the possibility of having conscious experiences without specific content challenges the idea that being conscious necessarily involves being conscious of something. Finally, by reviewing the literature on the neural correlates of consciousness, we propose a potential convergence in the study of conscious states and contents.

Journal of Sleep ResearchEarly View e14160 LETTER TO THE EDITOR Probing the embodiment of sleep functions: Insights from cardiac responses to word-induced relaxation during sleep Matthieu Koroma, Corresponding Author Matthieu Koroma [email protected] orcid.org/0000-0003-2269-7841 Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Fund for Scientific Research FNRS, Brussels, Belgium Sleep & Chronobiology Laboratory, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Correspondence Matthieu Koroma and Athena Demertzi, Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging Center, University of Liège, Allée du 6 Août, 8 (B30), 4000 Sart Tilman, Liège, Belgium. Email: [email protected] and [email protected] Contribution: Conceptualization, ​Investigation, Writing - original draft, Methodology, Validation, Visualization, Writing - review & editing, Project administration, Formal analysis, Software, Data curation, Resources, Funding acquisition, SupervisionSearch for more papers by this authorJonas Beck, Jonas Beck orcid.org/0000-0002-4637-5911 Swiss Sleep House Bern, Department of Neurology, Inselspital, Bern, Switzerland Contribution: ​Investigation, Validation, Formal analysis, Data curation, Visualization, Writing - review & editing, Methodology, ResourcesSearch for more papers by this authorChristina Schmidt, Christina Schmidt orcid.org/0000-0002-9867-012X Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Fund for Scientific Research FNRS, Brussels, Belgium Sleep & Chronobiology Laboratory, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Psychology & Neuroscience of Cognition (PsyNCog), University of Liège, Liège, Belgium Contribution: Conceptualization, Writing - original draft, Methodology, Validation, Visualization, Project administration, Formal analysis, Supervision, Writing - review & editing, Funding acquisitionSearch for more papers by this authorBjörn Rasch, Björn Rasch orcid.org/0000-0001-7607-3415 Department of Psychology, University of Fribourg, Fribourg, Switzerland Contribution: Data curation, Resources, Project administration, Formal analysis, Visualization, Validation, Funding acquisition, ​Investigation, Conceptualization, Supervision, Methodology, Writing - review & editingSearch for more papers by this authorAthena Demertzi, Corresponding Author Athena Demertzi [email protected] orcid.org/0000-0001-8021-3759 Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Fund for Scientific Research FNRS, Brussels, Belgium Sleep & Chronobiology Laboratory, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Psychology & Neuroscience of Cognition (PsyNCog), University of Liège, Liège, Belgium Correspondence Matthieu Koroma and Athena Demertzi, Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging Center, University of Liège, Allée du 6 Août, 8 (B30), 4000 Sart Tilman, Liège, Belgium. Email: [email protected] and [email protected] Contribution: Supervision, Conceptualization, ​Investigation, Validation, Visualization, Writing - review & editing, Formal analysis, Project administration, Resources, Data curation, Methodology, Writing - original draft, Funding acquisitionSearch for more papers by this author Matthieu Koroma, Corresponding Author Matthieu Koroma [email protected] orcid.org/0000-0003-2269-7841 Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Fund for Scientific Research FNRS, Brussels, Belgium Sleep & Chronobiology Laboratory, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Correspondence Matthieu Koroma and Athena Demertzi, Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging Center, University of Liège, Allée du 6 Août, 8 (B30), 4000 Sart Tilman, Liège, Belgium. Email: [email protected] and [email protected] Contribution: Conceptualization, ​Investigation, Writing - original draft, Methodology, Validation, Visualization, Writing - review & editing, Project administration, Formal analysis, Software, Data curation, Resources, Funding acquisition, SupervisionSearch for more papers by this authorJonas Beck, Jonas Beck orcid.org/0000-0002-4637-5911 Swiss Sleep House Bern, Department of Neurology, Inselspital, Bern, Switzerland Contribution: ​Investigation, Validation, Formal analysis, Data curation, Visualization, Writing - review & editing, Methodology, ResourcesSearch for more papers by this authorChristina Schmidt, Christina Schmidt orcid.org/0000-0002-9867-012X Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Fund for Scientific Research FNRS, Brussels, Belgium Sleep & Chronobiology Laboratory, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Psychology & Neuroscience of Cognition (PsyNCog), University of Liège, Liège, Belgium Contribution: Conceptualization, Writing - original draft, Methodology, Validation, Visualization, Project administration, Formal analysis, Supervision, Writing - review & editing, Funding acquisitionSearch for more papers by this authorBjörn Rasch, Björn Rasch orcid.org/0000-0001-7607-3415 Department of Psychology, University of Fribourg, Fribourg, Switzerland Contribution: Data curation, Resources, Project administration, Formal analysis, Visualization, Validation, Funding acquisition, ​Investigation, Conceptualization, Supervision, Methodology, Writing - review & editingSearch for more papers by this authorAthena Demertzi, Corresponding Author Athena Demertzi [email protected] orcid.org/0000-0001-8021-3759 Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Fund for Scientific Research FNRS, Brussels, Belgium Sleep & Chronobiology Laboratory, GIGA-CRC In Vivo Imaging, GIGA Institute, University of Liège, Liège, Belgium Psychology & Neuroscience of Cognition (PsyNCog), University of Liège, Liège, Belgium Correspondence Matthieu Koroma and Athena Demertzi, Physiology of Cognition Lab, GIGA-CRC In Vivo Imaging Center, University of Liège, Allée du 6 Août, 8 (B30), 4000 Sart Tilman, Liège, Belgium. Email: [email protected] and [email protected] Contribution: Supervision, Conceptualization, ​Investigation, Validation, Visualization, Writing - review & editing, Formal analysis, Project administration, Resources, Data curation, Methodology, Writing - original draft, Funding acquisitionSearch for more papers by this author First published: 14 February 2024 https://doi.org/10.1111/jsr.14160Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Open Research DATA AVAILABILITY STATEMENT The data that support the findings of this study are openly available in OSF at https://osf.io/jn7ar/, reference number doi:10.17605/OSF.IO/JN7AR. REFERENCES Azzalini, D., Rebollo, I., & Tallon-Baudry, C. (2019). Visceral signals shape brain dynamics and cognition. Trends in Cognitive Sciences, 23(6), 488–509. https://doi.org/10.1016/j.tics.2019.03.007 10.1016/j.tics.2019.03.007 PubMedWeb of Science®Google Scholar Beck, J., Loretz, E., & Rasch, B. (2021). Exposure to relaxing words during sleep promotes slow-wave sleep and subjective sleep quality. Sleep, 44(11), zsab148. https://doi.org/10.1093/sleep/zsab148 10.1093/sleep/zsab148 PubMedWeb of Science®Google Scholar Chouchou, F., & Desseilles, M. (2014). Heart rate variability: A tool to explore the sleeping brain? Frontiers in Neuroscience, 8, 402. https://doi.org/10.3389/fnins.2014.00402 10.3389/fnins.2014.00402 PubMedWeb of Science®Google Scholar Kluyver, T., Ragan-Kelley, B., Pérez, F., Granger, B. E., Bussonnier, M., Frederic, J., Kelley, K., Hamrick, J. B., Grout, J., Corlay, S., & Ivanov, P. (2016). Jupyter notebooks – A publishing format for reproducible computational workflows. Position Power Acad Publ Play Agents Agendas. Google Scholar Oudiette, D., & Paller, K. A. (2013). Upgrading the sleeping brain with targeted memory reactivation. Trends in Cognitive Sciences, 17(3), 142–149. https://doi.org/10.1016/j.tics.2013.01.006 10.1016/j.tics.2013.01.006 PubMedWeb of Science®Google Scholar Park, H. D., & Tallon-Baudry, C. (2014). The neural subjective frame: From bodily signals to perceptual consciousness. Transactions of the Royal Society B: Biological Sciences, 369(1641), 20130208. https://doi.org/10.1098/rstb.2013.0208 10.1098/rstb.2013.0208 PubMedWeb of Science®Google Scholar Raimondo, F., Rohaut, B., Demertzi, A., Valente, M., Engemann, D. A., Salti, M., Fernandez Slezak, D., Naccache, L., & Sitt, J. D. (2017). Brain-heart interactions reveal consciousness in noncommunicating patients: Brain-heart interactions. Annals of Neurology, 82(4), 578–591. https://doi.org/10.1002/ana.25045 10.1002/ana.25045 PubMedWeb of Science®Google Scholar Wei, Y., & Van Someren, E. J. (2020). Interoception relates to sleep and sleep disorders. Current Opinion in Behavioral Sciences, 33, 1–7. https://doi.org/10.1016/j.cobeha.2019.11.008 10.1016/j.cobeha.2019.11.008 Web of Science®Google Scholar Whitehurst, L. N., Cellini, N., McDevitt, E. A., Duggan, K. A., & Mednick, S. C. (2016). Autonomic activity during sleep predicts memory consolidation in humans. Proceedings of the National Academy of Sciences, 113(26), 7272–7277. https://doi.org/10.1073/pnas.1518202113 10.1073/pnas.1518202113 CASPubMedWeb of Science®Google Scholar Whitehurst, L. N., Chen, P. C., Naji, M., & Mednick, S. C. (2020). New directions in sleep and memory research: The role of autonomic activity. Current Opinion in Behavioral Sciences, 33, 17–24. https://doi.org/10.1016/j.cobeha.2019.11.001 10.1016/j.cobeha.2019.11.001 Web of Science®Google Scholar Early ViewOnline Version of Record before inclusion in an issuee14160 ReferencesRelatedInformation

Ketamine is classified as a dissociative anaesthetic that, in sub-anaesthetic doses, can produce an altered state of consciousness characterised by dissociative symptoms, visual and auditory hallucinations, and perceptual distortions. Given the anaesthetic-like and psychedelic-like nature of this compound, it is expected to have different effects on brain dynamics in anaesthetic doses than in low, sub-anaesthetic doses. We investigated this question using connectome harmonic decomposition (CHD), a recently developed method to decompose brain activity in terms of the network organisation of the underlying human structural connectome. Previous research using this method has revealed connectome harmonic signatures of consciousness and responsiveness, with increased influence of global network structure in disorders of consciousness and propofol-induced sedation, and increased influence of localised patterns under the influence of classic psychedelics and sub-anaesthetic doses of ketamine, as compared to normal wakefulness. When we applied the CHD analytical framework to resting-state fMRI data of volunteers during ketamine-induced unresponsiveness, we found increased prevalence of localised harmonics, reminiscent of altered states of consciousness. This is different from traditional GABAergic sedation, where instead the prevalence of global rather than localised harmonics seems to increase with higher doses. In addition, we found that ketamine’s harmonic signature shows higher alignment with those seen in LSD- or psilocybin-induced psychedelic states than those seen in unconscious individuals, whether due to propofol sedation or brain injury. Together, the results indicate that ketamine-induced unresponsiveness, which does not necessarily suppress conscious experience, seems to influence the prevalence of connectome harmonics in the opposite way compared to GABAergic hypnotics. We conclude that the CHD framework offers the possibility to track alterations in conscious awareness (e.g., dreams, sensations) rather than behavioural responsiveness – a discovery made possible by ketamine’s unique property of decoupling these two facets. ### Competing Interest Statement VB has had financial relationships with the following companies: Orion Pharma, Medtronic, Edwards, and Elsevier. All other authors declare they have no competing interests.

Accurately predicting functional outcomes for unresponsive patients with acute brain injury is a medical, scientific and ethical challenge. This prospective study assesses how a multimodal approach combining various numbers of behavioral, neuroimaging and electrophysiological markers affects the performance of outcome predictions. We analyzed data from 349 patients admitted to a tertiary neurointensive care unit between 2009 and 2021, categorizing prognoses as good, uncertain or poor, and compared these predictions with observed outcomes using the Glasgow Outcome Scale–Extended (GOS-E, levels ranging from 1 to 8, with higher levels indicating better outcomes). After excluding cases with life-sustaining therapy withdrawal to mitigate the self-fulfilling prophecy bias, our findings reveal that a good prognosis, compared with a poor or uncertain one, is associated with better one-year functional outcomes (common odds ratio (95% CI) for higher GOS-E: OR = 14.57 (5.70–40.32), P < 0.001; and 2.9 (1.56–5.45), P < 0.001, respectively). Moreover, increasing the number of assessment modalities decreased uncertainty (OR = 0.35 (0.21–0.59), P < 0.001) and improved prognostic accuracy (OR = 2.72 (1.18–6.47), P = 0.011). Our results underscore the value of multimodal assessment in refining neuroprognostic precision, thereby offering a robust foundation for clinical decision-making processes for acutely brain-injured patients. ClinicalTrials.gov registration: NCT04534777.

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.

To provide insights into neurophenomenological richness after psilocybin intake, we investigated the link between dynamical brain patterns and the ensuing phenomenological pattern after psilocybin intake. Healthy participants received either psilocybin (n=22) or placebo (n=27) while in ultra-high field 7T MRI scanning. Changes in the phenomenological patterns were quantified using the 5-Dimensional Altered States of Consciousness (5D-ASC) Rating Scale, revealing alterations across all dimensions under psilocybin. Changes in the neurobiological patterns displayed that psilocybin induced widespread increases in averaged functional connectivity. Time-varying connectivity analysis unveiled a recurrent hyperconnected pattern characterized by low BOLD signal amplitude, suggesting heightened cortical arousal. In terms of neurophenomenology, canonical correlation analysis primarily linked the transition probabilities of the hyperconnected pattern with feelings of oceanic boundlessness (OBN), and secondly with visionary restructuralization. We suggest that the brain’s tendency to enter a hyperconnected-hyperarousal pattern under psilocybin represents the potential to entertain variant mental associations. For the first time, these findings link brain dynamics with phenomenological alterations, providing new insights into the neurophenomenology and neurophysiology of the psychedelic state.

Our ability to process environmental stimuli varies during sleep. Although much research focused on neural processing, emerging evidence shows that bodily signals may play a key role in understanding high-level sensory processing during sleep. Here, we tested how cardiac responses to the local-global paradigm, a typical oddball task probing the processing of simple (local) and complex (global) sensory irregularities. To do so, we analyzed electrocardiography (ECG) signals in a total of 56 participants from two existing datasets which contained cerebral responses to local auditory irregularities, but which did not analyze the ECG data before. We found that cardiac activity slowed down after global, but not local, auditory irregularities, revealing the presence of global deviance effect in Rapid Eye Movement (REM) sleep. In contrast, cardiac activity was faster after local, but not global, deviants in Non-Rapid Eye Movement (NREM) sleep. Overall, our results demonstrate that cardiac responses to auditory irregularities inform about hierarchical information processing and its variations during sleep beyond cerebral activity. They highlight the embodiment of cognitive function and the value of cardiac signals to understand the variations of sensory processing during sleep. ### Competing Interest Statement The authors have declared no competing interest.

A target question for the scientific study of consciousness is how dimensions of consciousness, such as the ability to feel pain and pleasure or reflect on one's own experience, vary in different states and animal species. Considering the tight link between consciousness and moral status, answers to these questions have implications for law and ethics. Here we point out that given this link, the scientific community studying consciousness may face implicit pressure to carry out certain research programs or interpret results in ways that justify current norms rather than challenge them. We show that because consciousness largely determines moral status, the use of nonhuman animals in the scientific study of consciousness introduces a direct conflict between scientific relevance and ethics-the more scientifically valuable an animal model is for studying consciousness, the more difficult it becomes to ethically justify compromises to its well-being for consciousness research. Finally, in light of these considerations, we call for a discussion of the immediate ethical corollaries of the body of knowledge that has accumulated and for a more explicit consideration of the role of ideology and ethics in the scientific study of consciousness.

Hypnosis has been shown to be of clinical utility; however, its underlying neural mechanisms remain unclear. This study aims to investigate altered brain dynamics during the non-ordinary state of consciousness induced by hypnosis. We studied high-density EEG in 9 healthy participants during eyes-closed wakefulness and during hypnosis, induced by a muscle relaxation and eyes fixation procedure. Using hypotheses based on internal and external awareness brain networks, we assessed region-wise brain connectivity between six ROIs (right and left frontal, right and left parietal, upper and lower midline regions) at the scalp level and compared across conditions. Data-driven, graph-theory analyses were also carried out to characterize brain network topology in terms of brain network segregation and integration. During hypnosis, we observed (1) increased delta connectivity between left and right frontal, as well as between right frontal and parietal regions; (2) decreased connectivity for alpha (between right frontal and parietal and between upper and lower midline regions) and beta-2 bands (between upper midline and right frontal, frontal and parietal, also between upper and lower midline regions); and (3) increased network segregation (short-range connections) in delta and alpha bands, and increased integration (long-range connections) in beta-2 band. This higher network integration and segregation was measured bilaterally in frontal and right parietal electrodes, which were identified as central hub regions during hypnosis. This modified connectivity and increased network integration-segregation properties suggest a modification of the internal and external awareness brain networks that may reflect efficient cognitive-processing and lower incidences of mind-wandering during hypnosis.