Biology subjects

Demertzi, A.

Publications and source records attributed to Demertzi, A..

15 recordsLinked to original sources

bioRxiv2026

How to Catch a Blank Mind? Brain Similarities and Differences between Self- and Probe-Caught Mind Blanking

Mind Blanking (MB) is a mental state characterized by the experience of a seemingly empty mind. This apparent emptiness challenges the theoretical view of a continuous and content-full stream of thought, leading to the question of how it is possible to capture MB events in the first place. MB research has relied largely on probe-caught experience-sampling, during which participants are interrupted at random times to report their mental state. This approach risks missing some MB events as they may occur between probes. Self-caught paradigms, on the other hand, allow participants to report MB upon spontaneously realizing it, relying on meta-awareness. To date, it is not clear whether these two methods capture the same phenomenon neuronally. Here, we investigated whether probe-caught MB (pMB) and self-caught MB (sMB) converge on their behavioral properties and brain correlates. Twenty-two participants underwent 3T fMRI scanning while performing both a pMB and a sMB experience-sampling task. We compared the behavioral properties, BOLD activations and time-varying functional connectivity (FC) across the two approaches. We found that reporting frequencies of pMB and sMB were significantly correlated across individuals, and both MB reports were uniformly distributed over time, pointing towards a behavioral convergence across approaches. However, we observed a divergence in BOLD activations, as sMB recruited significantly greater activation in the dorsal anterior cingulate cortex (dACC) compared to pMB, likely reflecting the meta-awareness and metacognitive monitoring required for self-detecting a MB. Lastly, time-varying FC analysis revealed a convergence, with both pMB and sMB FC resembling a hyperconnectivity pattern compared to other content-full mental states, pointing towards low arousal FC. Together, our results show that sMB and pMB converge on overlapping neurobehavioral correlates. This positions the self-caught method as a complementary tool for studying MB without external interruption, while highlighting the role of meta-awareness in self-report detection.

neuroscience↗

bioRxiv2026

The blueprint of human functional architecture shifts from cognition to anatomy during perturbations of consciousness

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 anatomicalmolecular constraints during pharmacological and pathological perturbations of consciousness.

neuroscience↗

bioRxiv2026

Heartbeat-locked auditory deviations slow down cardiac activity

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 statementUsing 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.

physiology↗

bioRxiv2025

Distinct cortical profiles underlie the common reportability of thought-free experiences

Mind blanking (MB) refers to moments of seemingly no reportable thought content, challenging the view of a constant thought-full mind. What remains unclear is which brain modes can lead to MB and why. Here, we aimed at delineating the nuances of MB by combining EEG-fMRI with experience-sampling of thought content and self-reported vigilance. Using a dynamic framework, we show that MB is linked to a "rich" fMRI connectivity pattern of regional anticorrelations, while low vigilance is linked to a "simple" pattern of overall positive connectivity. Put together, an interaction appears: when people are alert, connectivity around MB resembles the hyperconnected pattern, indicating that the neural correlates of MB depend on vigilance levels. This hyperconnected pattern further correlated with EEG slow-wave-like activity, tying MBs topology to sleep-like electrophysiology. We conclude that MBs neurophysiological correlates vary with vigilance, and a more refined characterisation of the neural correlates of thought-free states exists.

neuroscience↗

bioRxiv2024

Cardiac responses to auditory irregularities reveal hierarchical information processing during sleep

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.

neuroscience↗

bioRxiv2024

Ketamine-Induced Unresponsiveness Shows a Harmonic Shift from Global to Localised Functional Organisation.

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 ketamines 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 ketamines unique property of decoupling these two facets.

neuroscience↗

bioRxiv2024

Variations of autonomic arousal mediate the reportability of mind-blanking occurrences

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 number 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 show 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.

neuroscience↗

bioRxiv2023

Altered subjective experience after psilocybin intake associates with a dynamic pattern of hyperconnected functional connectivity

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 brains 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.

neuroscience↗

bioRxiv2023

Whole-brain deactivations precede uninduced mind-blanking reports

Mind-blanking (MB) is termed as the inability to report our immediate-past mental content. In contrast to mental states with reportable content, such as mind-wandering or sensory perceptions, the neural correlates of MB started getting elucidated only recently. A notable particularity that pertains to MB studies is the way MB is instructed for reporting, like by deliberately asking participants to "empty their minds". Such instructions were shown to induce fMRI activations in frontal brain regions, typically associated with metacognition and self-evaluative processes, suggesting that MB may be a result of intentional mental content suppression. Here, we aim at examining this hypothesis by determining the neural correlates of MB without induction. Using fMRI combined with experience-sampling in 31 participants (22 female), univariate analysis of MB reports revealed deactivations in occipital, frontal, parietal, and thalamic areas, but no activations in prefrontal regions. These findings were confirmed using Bayesian region-of-interest analysis on areas previously shown to be implicated in induced MB, where we report evidence for frontal deactivations during MB reports compared to other mental states. Contrast analysis between reports of MB and content-oriented mental states also revealed deactivations in the left angular gyrus. We propose that these effects characterize a neuronal profile of MB, where key thalamocortical nodes are unable to communicate and formulate reportable content. Collectively, we show that study instructions for MB lead to differential neural activation. These results provide mechanistic insights linked to the phenomenology of MB and point to the possibility of MB being expressed in different forms.

neuroscience↗

bioRxiv2022

Low-dimensional organization of global brain states of reduced consciousness

Brain states are frequently represented using a unidimensional scale measuring the richness of subjective experience (level of consciousness). This description assumes a mapping between the high-dimensional space of whole-brain configurations and the trajectories of brain states associated with changes in consciousness, yet this mapping and its properties remain unknown. We combined whole-brain modelling, data augmentation and deep learning for dimensionality reduction to determine a mapping representing states of consciousness in a low-dimensional space, where distances parallel similarities between states. An orderly trajectory from wakefulness to brain injured patients is revealed in a latent space whose coordinates represent metrics related to functional modularity and structure-function coupling, both increasing alongside loss of consciousness. Finally, we investigated the effects of model perturbations, providing geometrical interpretation for the stability and reversibility of states. We conclude that conscious awareness depends on functional patterns encoded as a low-dimensional trajectory within the vast space of brain configurations.

neuroscience↗

bioRxiv2022

Age-dependent attentional style and pupil-linked arousal regulate the reportability of spontaneous mental states

Spontaneous thinking significantly relies on attention and arousal. As these cognitive faculties change with age, we aimed at providing a comprehensive account to ongoing mental states in seniors, testing how these are influenced by attentional control and arousal. Using experience sampling at rest, 20 senior (65-75yrs) and 20 young participants (20-30yrs) were prompted to report mind-wandering (MW), sensory-related thoughts (S), and the newly introduced state of mind blanking (MB). Attentional control was assessed with the Attentional Style Questionnaire, and arousal with continuous monitoring of pupil diameter. Both age groups showed equally high occurrences of MW compared to MB or S. For young responders, we replicated that MW was more prevalent in easily-distracted participants and that it associated with higher arousal. In seniors, though, MB was more prevalent in easily-distracted participants, and it was associated with higher arousal, reversing the pattern found in young adults and focused seniors. Overall, our results show that attentional control and arousal jointly regulate ongoing mental states in an age-dependent manner and uncover the presence a specific profile of ongoing mental state regulation in healthy aging, being a potentially critical marker of age-associated diseases.

neuroscience↗

bioRxiv2021

Mind blanking is associated with a rigid spatio-temporal profile in typical wakefulness

Mind blanking (MB) is a waking state during which we do not report any mental content, challenging the view of a constantly thought-oriented brain. Here, we comprehensively characterize the MBs neurobehavioral profile with the aim to delineate its role during ongoing mentation. Using fMRI experience-sampling, we show that MB is reported less frequently, faster, and with low transitional dynamics among other mental states, pointing to its role as a transient mental relay. Regarding its neural underpinnings, we observe higher global signal amplitude during MB reports, indicating a distinct physiological substrate. Using the time-varying functional connectome MB reports get classified with high accuracy, suggesting that MB has a unique neural composition. Indeed, a pattern of globally positive-phase coherence shows the highest similarity to the connectivity patterns associated with MB reports. We observe that this patterns rigid signal architecture hinders content reportability due to the brains inability to differentiate signals in an informative way. Collectively, we show that MB has a unique neurobehavioural profile, indicating that non-reportable mental events can happen during wakefulness. Our results add to the characterization of spontaneous mentation and pave the way for more mechanistic investigations of MBs phenomenology. Significance StatementThe human mind is generally assumed to be thought-oriented. Mind blanking (MB) challenges this stance because it appears as if we are derived of any particular mental content to report. We here show that, during spontaneous thinking, MB is a mental state that happens by default, it has a unique behavioural profile, and it is of a rigid neural architecture that does not permit the formulation of reportable contents. Our work essentially proposes that non-reportable mental events can happen during wakefulness, and challenges the view of the mind as a constant thought-oriented operator.

neuroscience↗

bioRxiv2020

Perturbations in dynamical models of whole-brain activity dissociate between the level and stability of consciousness

Consciousness transiently fades away during deep sleep, more stably under anesthesia, and sometimes permanently due to brain injury. The development of an index to quantify the level of consciousness across these different states is regarded as a key problem both in basic and clinical neuroscience. We argue that this problem is ill-defined since such an index would not exhaust all the relevant information about a given state of consciousness. While the level of consciousness can be taken to describe the actual brain state, a complete characterization should also include its potential behavior against external perturbations. We developed and analyzed whole-brain computational models to show that the stability of conscious states provides information complementary to their similarity to conscious wakefulness. Our work leads to a novel methodological framework to sort out different brain states by their stability and reversibility, and illustrates its usefulness to dissociate between physiological (sleep), pathological (brain-injured patients), and pharmacologically-induced (anesthesia) loss of consciousness.

neuroscience↗

bioRxiv2019

The Time Varying Networks of the Interoceptive Attention and Rest

Focused attention to spontaneous sensations is a phenomenon that demands interoceptive abilities and a dynamic character of attentive processes. The lack of its control has been linked to neuropsychiatric disorders, such as illness-anxiety disorder. Regulatory strategies, like focused attention meditation, may enhance the ability to control attention particularly to body sensations, which can be reflected on functional neuroanatomy. Adopting a systems-level approach, we aimed at estimating the recurring fMRI functional connectivity (FC) patterns between regions of the dorsal attention network, default mode network, and frontoparietal network during 20 minutes of an attentional task to spontaneous sensations (Task), and at rest, before (Pre-task rs) and after the task (Post-task rs), in fifteen experienced meditators. Dynamic functional connectivity analysis was performed using sliding windows and k-means clustering on the grouped data finding five FC patterns. In both rest conditions the subjects remain longer in a low connectivity state, in contrast, during the task a higher proportion of time spent in complex organization states was preferred. Moreover, an impact over the post-task rs FC was observed as an effect of the preceding interoceptive task performance, with this remaining effect probably taking an active role in the learning process linked to cognitive training.Competing Interest StatementThe authors have declared no competing interest.View Full Text

neuroscience↗

bioRxiv2019

Functional cortico-subcortical reorganization after complete hemispheric disconnection for intractable epilepsy

Hemispherotomy is a treatment for drug-resistant epilepsy with the whole hemisphere involved in seizure onset. As recovery mechanisms are still debated, we characterize functional reorganization with multimodal MRI in two children operated on the right hemisphere (RH). We found that interhemispheric functional connectivity was abolished in both patients. The healthy left hemispheres (LH) displayed focal hyperperfusion in motor and limbic areas, and preserved network-level organization. The disconnected RHs were hypoperfused despite sustained network-level organization. Functional connectivity was increased in the left thalamo-cortical loop and between the cerebelli. The classification probability of the RH corresponding to a minimally conscious state was smaller than for the LH. We conclude that after hemispherotomy, neurological rehabilitation is sustained by cortical disinhibition and reinforcement of connectivity driven by subcortical structures in the remaining hemisphere. Our results highlight the effect of vascularization on functional connectivity and raise inquiries about the conscious state of the isolated hemisphere.

neuroscience↗