Biology subjects

Andrillon, T.

Publications and source records attributed to Andrillon, T..

At least 19 recordsLinked to original sources

bioRxiv2026

REM Sleep Iota Oscillations Across the Lifespan

Iota oscillations are a newly discovered marker of wakefulness and rapid eye movement (REM) sleep. So far, iota in REM sleep has only been reported in the surface electroencephalography (EEG) of a small sample of young adults and in intracranial recordings of epileptic patients. Here, we investigated the presence of these oscillations in a large dataset (N=937) of high-density sleep EEG recordings from individuals 7 to 70 years old. We found that iota spectral peaks during REM sleep were between 25 and 40 Hz, slightly faster than in wake (25-35 Hz). Iota power was significantly associated with REM sleep architecture, increasing with both REM duration and across progressive sleep cycles. Iota peaks were observed in individuals of all ages, although the prevalence decreased gradually with age, from 88% in children to 44% in older adults. Most iota spectral peak properties (frequency, amplitude, timing, topography) likewise shifted with age. The most striking effect, however, was in bandwidth, such that children had narrow iota peaks, older adults had broad iota peaks, and 20-30 year olds could have either. It remains unclear whether narrowband and broadband iota are functionally equivalent. On shorter time scales (< 1 year), iota properties remained stable across measurements. Analyses of a separate dataset of monozygotic and dizygotic twins revealed high heritability of all iota peak properties except bandwidth. Overall, these results establish iota as a genetically determined trait-like marker of REM sleep with unique age-related changes. Iota oscillations open new avenues to investigate the interaction between sleep, genetics, development, and aging.

neuroscience↗

bioRxiv2026

Spontaneous slow waves index multiple dimensions of recovery in Disorders of Consciousness

Whether and how residual awareness is expressed in patients with Disorders of Consciousness (DoC) depends on the severity of brain damage and the transient functional state of the cortex at assessment. Classically, DoC are associated with electroencephalographic (EEG) slowing, marked by high-amplitude slow waves, even during the day. Yet, slow waves are also a hallmark of healthy sleep, where they are thought to serve restorative functions and to help maintain network homeostasis. Here, we asked whether slow waves in DoC can provide insights into the severity of cortical dysfunction or, conversely, into the preservation of residual awareness and recovery potential, by characterizing their spatial, temporal and morphological properties. We analyzed 256-channel EEG recorded during the Local-Global auditory paradigm in 236 DoC patients, including 123 in Unresponsive Wakefulness Syndrome (UWS), 62 in a Minimally Conscious State minus (MCS-) and 29 in MCS plus (MCS+). High-amplitude slow waves were detected as local events, and their density, amplitude and slopes were quantified scalp-wide and channel-wise, by mean level and temporal variability across the recording. Slow-wave features were related to concurrent (Coma Recovery Scale-Revised - CRS-R, Local-Global paradigm) and follow-up (one-year Glasgow Outcome Scale-Extended - GOS-E) assessments of consciousness and functional recovery. Associations with MRI-derived measures of cortical integrity and structural connectivity, and differences between anoxic and traumatic etiologies, were also examined. Slow waves were more frequent in less severe DoC patients (i.e., MCS) compared to UWS. Slow-wave slopes were also steeper frontally and increased at a faster rate in patients exhibiting higher levels of consciousness and/or markers of conscious access during the Local-Global paradigm. More frequent and steeper slow waves at baseline further predicted recovery of consciousness and of functional independence at one year. At the individual level, slow-wave features classified states of consciousness above chance (AUC = 0.62 and 0.71 for MCS- and MCS+ versus UWS), whereas outcome prediction remained modest (0.56-0.58). These clinical associations had a structural basis: slow-wave occurrence was greater after traumatic than anoxic injury and scaled with the integrity of subcortico-cortical projection fibers and consciousness-related cortical networks. Contrary to the classical view of delta activity as a non-specific marker of impaired consciousness, prominent spontaneous slow waves indexed behavioral and neurophysiological signs of awareness and better recovery. Beyond reflecting a propensity for pathological bistability, they may also signal the integrity of the networks required to generate them, together with their residual capacity for dynamic regulation.

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bioRxiv2026

Diminished Stimulus-Evoked Activity During Sustained Attention Without Behavioural Cost in ADHD

Attention-Deficit/Hyperactivity Disorder (ADHD) is often accompanied by attentional challenges, sleep difficulties and increased reports of daytime sleepiness, indicating potential links between attention and arousal mechanisms. Electroencephalographic (EEG) studies have shown that sleep-like wake slow wave (SW) activity during wakefulness, characterised by reduced cortical activity, corresponds with periods of inattention in both ADHD and neurotypical populations. However, it remains unclear whether group differences in waking SWs are consistent across different types of sustained attention tasks or may be context-dependent. The present study compared sustained attention performance and wake SW activity between adults with and without ADHD during a continuous visual target detection task. EEG data were collected while adults with (n = 52) and without ADHD (n = 49) completed a sustained attention paradigm. The task presented a continuous stream of rotating (anti-clockwise or clockwise) black-and-white checkerboard stimuli, and participants were required to detect infrequent targets that were marginally longer in duration than non-targets. Behavioural and neural measures (power spectra, steady-state visually evoked potentials (SSVEP), event-related potentials and SW density during wake) were analysed. No significant group differences were observed for task performance and wake SW activity. However, electrophysiological analyses revealed the ADHD group showed reduced P300, elevated beta-band power, and lower SSVEPs to target stimuli compared with the neurotypical group. These neural differences in the context of comparable performance suggest compensatory cortical recruitment in ADHD. The absence of SW differences further supports this, suggesting comparable performance and maintained arousal may reflect successful neural compensation in ADHD in this cognitive task. Significance StatementIndividuals with ADHD commonly experience attention differences, but emerging evidence suggests these difficulties may depend on task context. Using clinical diagnostic interviews, medication washout, and Bayesian statistics, we found strong evidence for comparable performance between ADHD and neurotypical adults on a sustained attention task. Notably, slow wave activity during wakefulness did not differ between groups, consistent with maintained arousal. Nevertheless, differences in brain activity, including altered target processing, increased cortical activation and reduced visual entrainment, suggested compensatory neural recruitment in ADHD. This context-dependent pattern has important theoretical and clinical implications: identifying task features that challenge or support performance in ADHD can reveal how individuals compensate neurally, and guide interventions that leverage task features to support attention in ADHD.

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bioRxiv2026

Opposite Effects of Alpha Oscillations on Mind-Wandering With Eyes Open and Closed

Spontaneous fluctuations in brain activity are thought to underlie mind-wandering, moments when mental experience becomes unrelated to what one is currently doing. A large body of research has investigated ongoing neural oscillations in the alpha band (7-14 Hz), reflecting changes in arousal and attention. However, studies disagree whether the power of alpha oscillations increases or decreases during mind-wandering compared to on-task focus. We hypothesized that these opposite effects arise from differences in eye state across studies, as eye closure increases alpha power and can reverse alphas relationship with sleepiness, which is itself related to mind-wandering. To test this, we recorded EEG while male and female participants with eyes either open or closed were probed to report whether they were focused on the auditory attention task or mind-wandering, as well as how sleepy they were. Consistent with our hypothesis, we found that increased alpha power made both mind-wandering and sleepiness more likely in the eyes-open group but less likely in the eyes-closed group. A systematic review of past literature largely replicated these opposite relationships across eye states in different paradigms. We propose that these results reflect an inverted-U relationship between alpha power and mind-wandering, formed by a positive relationship at low alpha power values typical of eyes-open states and a negative relationship at high alpha power values typical of eyes-closed states. By sampling alpha power across eye states in the same paradigm, this work reconciles contradictions in prior literature and clarifies how ongoing neural oscillations reflect the stream of mental experiences. Significance StatementBrain signals tracked with electroencephalography (EEG) can provide a read-out of a persons current mental experience. Increases in a brain signal called alpha oscillations usually indicate sleepiness when recorded with eyes open. Surprisingly, the read-out can be reversed when eyes are closed: increases in alpha oscillations indicate alertness. Here, we found that this reversal explains the puzzling relationship between alpha oscillations and mind-wandering, when mental experience becomes unrelated to the task-at-hand. In moments of increased alpha, participants with eyes open reported more mind-wandering and sleepiness, whereas participants with eyes closed reported more on-task focus and alertness. One intriguing possibility is that decreases in arousal reflected by changes in alpha oscillations trigger episodes of mind-wandering.

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bioRxiv2026

The impact of homeostatic inhibitory plasticity in a generative biophysical model

A main characteristic of biological systems is their capacity to dynamically adapt to environmental changes. In the brain, synaptic plasticity enables the strengthening or weakening of connections between neurons, allowing neural circuits to adapt based on experience, learning, and environmental changes. Yet, it is homeostatically regulated such that it avoids excessive proliferation of synaptic contacts. These mechanisms can be studied with large-scale models of brain activity. Here, we embed a biologically grounded inhibitory-homeostatic plasticity rule into the Dynamic Mean Field (DMF) model, creating a Homeostatic Dynamic Mean Field (HDMF) model that dynamically tunes local excitation-inhibition balance. Convergence of excitatory firing rates is reached by mapping a large range of coupling strength to parameters of inhibitory synapses. The HDMF reproduces statistical observables of brain activity as well as the original DMF, and can sustain neuromodulatory perturbations without overhead computations. The HDMF can generate unprecedented sleep-like slow-wave activity, which can also coexist with wake-like asynchronous dynamics, permitting to model dissociated states of consciousness such as parasomnias. Together, these results show that a single homeostatic rule broadens the stability and expressiveness of the DMF, providing a unified platform for studying how local adaptive processes shape the diverse global dynamics of the human brain.

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bioRxiv2025

Sleep-like slow waves in wakefulness index post-stroke behavioural alterations

Increases in high-amplitude, low-frequency EEG oscillations during non-rapid eye movement (NREM) sleep serve as markers of neuronal silencing, which disrupts functional connectivity and is associated with a loss of awareness and responsiveness. Cortical slowing likewise occurs during wakefulness, upon sleep deprivation, and accompanies performance deterioration. Recent work has revealed similar oscillations (termed sleep-like slow waves) following stroke in brain regions close or connected to a brain lesion, offering a plausible but untested mechanism for stroke-related behavioural impairment. Here, we simultaneously recorded EEG and behavioural performance while 30 unilateral stroke patients (12 left hemisphere, 18 right hemisphere) and 27 age-matched healthy adults completed a computerised perceptual decision-making task. Sleep-like slow waves occurred more frequently in stroke patients relative to healthy controls. Furthermore, there was a significant correlation between slow wave occurrence and the accuracy and speed of perceptual reports in stroke patients, suggesting that variations in the occurrence of slow waves may contribute to cognitive heterogeneity post-stroke. Evidence that sleep-like slow waves predict deficits in perceptual decision-making following stroke indicates that stroke-induced lesions can destabilize cortical networks extending beyond the damaged regions, thereby contributing to broader cognitive impairments.

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bioRxiv2025

Ketamine disrupts consciousness in healthy participants in relation with psychotic-like symptoms

Ketamine is an NMDA-receptor antagonist, which alters the state of wakeful consciousness at high doses. At lower doses, it induces reversible psychotic-like symptoms and has been used as a pharmacological model of psychosis. In this study, we explore whether low doses of ketamine disrupt conscious access in relation with its psychotomimetic effects, and investigate the neural correlates of its action. We administered ketamine and placebo to 21 healthy volunteers following a double-blind within-subject randomized design and recorded brain activity with high-density electroencephalography during a perceptual task. Participants had to categorize a sound and a masked digit, and to report the digit visibility. To manipulate visibility, the delays between the sound, the digit, and the mask were varied. Principal component analysis was used to decompose ketamine-induced psychiatric symptoms and to examine their relationships with conscious access measures. Under ketamine, participants had an increased visual masking effect, more interference between the sound and the digit, and a reduced ability to consciously perceive the digit. The N1 component, a EEG marker of visual processing, correlated with conscious access and was significantly reduced under ketamine. Ketamine induced manic-like and psychotic-like symptoms but only the psychotic-like dimension correlated with conscious access impairments. Overall, our results suggest that ketamine disrupts conscious access in healthy subjects through an attenuation of early visual responses, and in relation with its psychotomimetic effects. Interestingly, these changes differed in part from those observed in patients with schizophrenia, opening new perspectives on the mechanisms of psychotic symptoms.

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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.

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bioRxiv2025

Sleep-like Slow Waves During Wakefulness Mediate Attention and Vigilance Difficulties in Adult Attention-Deficit/Hyperactivity Disorder

BackgroundAttention-Deficit/Hyperactivity Disorder (ADHD) is characterised by behavioural variability and heightened inattention associated with increased mind wandering (MW) and mind blanking (MB). Individuals with ADHD frequently experience sleep disorders and excessive daytime sleepiness, suggesting interactions between attention and arousal systems. Research examining brain activity using electroencephalography (EEG) has demonstrated that sleep-like slow waves (SW) during wakefulness are linked to inattention in neurotypical individuals, particularly following sleep deprivation, yet their role in ADHD remains unclear. This study investigated whether individuals with ADHD present with altered waking SW distribution compared to neurotypical controls and whether SW explain attentional difficulties in ADHD. MethodsAdults with (n = 32) and without ADHD (n = 31) completed a sustained attention task while EEG recorded brain activity. Mental state probes (on-task, MW, MB) were embedded within the task. Sleep-like SW reflect a slowing of cortical activity and was detected from EEG activity. Omission/commission errors, reaction time (RT), RT variability, mental state reports and subjective sleepiness were analysed. Mediation analysis examined whether SW density explained ADHD-related performance differences. ResultsIndividuals with ADHD exhibited more commission errors, MW and MB, and higher SW density (SW/min), particularly over parieto-temporal electrodes. Increased SW density correlated with higher omission errors, slower RTs, greater RT variability, and elevated sleepiness ratings. On-task reports were negatively correlated with SW density. Mediation analysis revealed that SW density significantly accounted for ADHD-related attentional difficulties. ConclusionsWake SW may explain attentional difficulties in ADHD, providing a potential mechanistic link between sleep disturbances and attentional fluctuations.

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bioRxiv2025

Dynamical independence reveals anaesthetic specific fragmentation of emergent structure in neural dynamics

Conscious experience depends on the coordinated activity of neural processes that span multiple scales--from synapses to whole-brain dynamics. A recently introduced measure, dynamical independence, identifies, characterises and quantifies these multi-scale relationships using an information-theoretic dimensionality-reduction approach. Here, we use DI to examine changes in emergent dynamical structure in the human brain under three pharmacologically-distinct anaesthetic interventions (propofol, xenon, ketamine). Applied to source-reconstructed EEG, our analysis reveals that propofol and xenon, anaesthetics that abolish conscious report, exhibit more emergent but highly variable dynamic structure, indicating fragmented macroscopic dynamical organisation. By contrast, ketamine, which preserves dream-like phenomenology, shows the opposite pattern: reduced overall emergence yet a partial preservation of the macroscopic structure, mirroring wake. Further exploratory analyses revealed spatially localised source-level contributions to emergent dynamical structure, highlighting regional variations. Together, our results highlight drug-specific reconfigurations of emergent dynamical structure under anaesthesia, dissociate the amount of emergence from the organisation of emergent dynamics, and caution against equating emergence with level of consciousness.

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bioRxiv2025

EEG Signature of Idiopathic Hypersomnia: Insights from Sleep Microarchitecture and Hypnodensity Metrics

Background and ObjectivesPatients with idiopathic hypersomnia with long sleep time (IH) report daytime hypersomnolence despite prolonged sleep time and normal sleep macrostructure. As they often have non-restorative sleep, we investigated whether the structure of their sleep is abnormal. MethodsIn polysomnography recordings from 80 IH participants and 48 controls, we quantified hypnodensity metrics across the night (macro level), periodic and aperiodic spectral properties, infraslow fluctuations of sigma power within the night (meso level), slow waves, sleep spindles and their clustering (microstructure). Multivariate machine-learning models were used to classify IH vs. control sleep. ResultsHypnodensity metrics were comparable between IH and controls, apart from more mixed wake/N1 sleep epochs in IH, and greater divergence between consecutive epochs of the same stage during NREM sleep in IH. Sigma power was increased in N2 sleep in IH and sleep spindles were more frequent and clustered. Slow wave density was higher in IH. Higher mean spindle cluster size correlated with higher Epworth Sleepiness Scale scores. Multivariate machine learning models incorporating these features achieved a balanced accuracy of 74% in distinguishing IH from controls. DiscussionWhile spindles and slow waves are typically associated with good sleep quality, they are increased in IH patients. This could reflect greater need for sleep and increased difficulty waking up in IH, which is also characterized by more mixed wake/N1 stages.

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bioRxiv2024

Capturing the emergent dynamical structure in biophysical neural models

Complex neural systems can display structured emergent dynamics. Capturing this structure remains a significant scientific challenge. Using information theory, we apply Dynamical Independence (DI) to uncover the emergent dynamical structure in a minimal 5-node biophysical neural model, shaped by the interplay of two key aspects of brain organisation: integration and segregation. In our study, functional integration within the biophysical neural model is modulated by a global coupling parameter, while functional segregation is influenced by adding dynamical noise, which counteracts global coupling. DI defines a dimensionally-reduced macroscopic variable (e.g., a coarse-graining) as emergent to the extent that it behaves as an independent dynamical process, distinct from the micro-level dynamics. We measure dynamical dependence (a departure from dynamical independence) for macroscopic variables across spatial scales. Our results indicate that the degree of emergence of macroscopic variables is relatively minimised at balanced points of integration and segregation and maximised at the extremes. Additionally, our method identifies to which degree the macroscopic dynamics are localised across microlevel nodes, thereby elucidating the emergent dynamical structure through the relationship between microscopic and macroscopic processes. We find that deviation from a balanced point between integration and segregation results in a less localised, more distributed emergent dynamical structure as identified by DI. This finding suggests that a balance of functional integration and segregation is associated with lower levels of emergence (higher dynamical dependence), which may be crucial for sustaining coherent, localised emergent macroscopic dynamical structures. This work also provides a complete computational implementation for the identification of emergent neural dynamics that could be applied both in silico and in vivo. Author summaryUnderstanding how complex neural systems give rise to emergent macroscopic patterns is a central challenge in neuroscience. Emergence, where macroscopic structures appear from underlying microscopic interactions, plays a crucial role in brain function, yet identifying the specific dynamics involved remains elusive. Traditionally, methods have quantified the extent of emergence but have struggled to pinpoint the emergent dynamical structure itself. In this study, we develop and apply a method, based on a quantity called Dynamical Independence (DI), which simultaneously captures the extent of emergence and reveals the underlying dynamical structure in neurophysiological data. Using a minimal 5-node biophysical neural model, we explore how a balance between functional integration and segregation--two key organisational principles in the brain--affects emergent macroscopic dynamics. Our results show that a finely balanced system produces highly localised, coherent macroscopic structures, while extreme deviations lead to more distributed, less localised dynamics. This work provides a computational framework for identifying emergent dynamical structure in both theoretical models and potentially in empirical brain data, advancing our understanding of the brains complex organisation across higher-order scales.

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bioRxiv2024

When your heart isn't in it anymore: Cardiac correlates of task disengagement

Neuroscience is beginning to uncover the role of interoceptive feedback in perception, learning, and decision-making; however, the relation between spontaneous visceral and cognitive dynamics has received surprisingly little scrutiny. Here, we investigate how subjective, physiological, and behavioural indicators of arousal and attentional state vary in relation to ongoing cardiac activity and brain-heart coupling. Electroencephalogram, electrocardiogram, and pupillometric records were obtained from 65 adults during the performance of a sustained attention to response task (SART). Thought probes were intermittently administered during the SART to collect subjective reports of attentional state (i.e., on-task, mind-wandering, mind-blanking) and vigilance level (i.e., alertness vs. sleepiness). Mind-wandering and mind-blanking reports increased in frequency with time-on-task and were accompanied by decreases in alertness and pupil-linked arousal, but evinced distinct psychophysiological and behavioural profiles. While mind-wandering was associated with greater heart-rate variability and late modulation of the heartbeat-evoked potential, mind-blanking was characterised by greater decreases in heart-rate, pupil size, and brain-heart coupling. Lower heart-rate predicted decreased vigilance and pupil size, in addition to slower, less-biased responses; increased heart-rate variability predicted more impulsive behaviour and pupil dilation. Together, these findings reveal that cardiac and brain-heart connectivity measures afford complementary information about arousal states and attentional dynamics during task performance.

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bioRxiv2024

Mind the blank: behavioral, experiential, and physiological signatures of absent-mindedness

Does being awake necessarily mean being conscious of something? This study investigates the phenomenon of Mind Blanking (MB), characterized by an "emptiness of mind", comparing it with Mind Wandering (MW) and On-task (ON) states. Using a sustained attention task and electroencephalogram monitoring, behavioral and neurophysiological signatures of MB were examined in 62 participants. MB exhibited a specific pattern of behavioral lapses, as well as decreased fast oscillatory activity and complexity over posterior electrodes compared to MW. Functional connectivity analyses revealed decreased long-range inter-areal connectivity during MB, compared to both ON and MW states. Event-related potentials with source reconstruction and temporal decoding techniques indicated a significant disruption in visual processing during MB, starting from 200 ms post stimulus and echoing into the late-stage of visual processing, suggesting a disruption of conscious access to sensory information during MB. EEG-derived markers allowed the prediction of mental states at the trial level, offering a finer view of conscious dynamics than subjective reports alone. Overall, these findings challenge the notion of the wakeful conscious mind as inherently content-oriented, suggesting that MB reflects genuine gaps in the stream of conscious thoughts, arising from disruptions in the generation or accessibility of thought content. SIGNIFICANCE STATEMENTEmploying cutting-edge neurophysiological techniques on high-density electroencephalographic recordings, our study unveils unique neurophysiological markers of mind blanking, a phenomenon characterized by lapses in conscious content amidst the flow of wakeful consciousness. Distinguished from content-oriented states such as on-task and mind-wandering, mind blanking appears to be a distinct mental state. Furthermore, we demonstrate the feasibility of decoding consciousness dynamics solely from EEG features, transcending the limitations of intermittent subjective reports. Our findings thus not only provide a novel framework for investigating the stream of consciousness but also challenge the conventional notion that wakefulness invariably signifies being conscious of something.

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bioRxiv2023

Heartbeat-evoked potential and ongoing brain dynamics during interoceptive and exteroceptive information processing predict attentional focus

Attention shapes our consciousness content and perception by increasing the probability of becoming aware and, or, better encode a selection of the incoming inner or outer sensory world. We designed a task to engage interoceptive and exteroceptive attention by orienting healthy participants to their heartbeats or auditory stimuli and investigated whether brain dynamics (Kolmogorov complexity - KC, permutation entropy - PE, weighted symbolic mutual information - wSMI, power spectrum density - PSD) and the heartbeat-evoked potential (HEP) distinguished interoceptive from exteroceptive covert attention. Exteroceptive attention yielded an overall flattening of the PSD, whereas during interoceptive attention there was a decrease in complexity, an increase in frontal connectivity and oscillations in the theta range, and a modulation of the HEP. Subject-level classifiers based on HEP features classified the attentional state of 17/20 participants. KC, PE, and wSMI showed comparable accuracy in classifying exteroceptive-interoceptive attention and exhibited a synergic behavior with the HEP features. PSD features demonstrated exceptional performance (20/20). Command-following was assessed in 5 brain-injured patients with a modified version of the task. An Unresponsive Wakefulness Syndrome/Vegetative State patient and a locked-in syndrome patient demonstrated a willful modulation of the HEP and the patient-level classifiers suggest that patients were complying with task instructions. Our findings show that directing attention to bodily rhythms or external stimuli elicits distinct neural responses that can be employed to track covert attention at the individual level. Importantly, the brain markers studied in this work provide multiple layers to explore information processing in disorders of conscious patients. Significance statementWe show that directing attention to bodily rhythms or external stimuli induces specific neural responses, allowing for individual-level tracking of covert attention in healthy participants. The time-locked and dynamical brain markers identified as relevant to distinguish between interoceptive-exteroceptive attention were further assessed in a small cohort of brain-injured patients as an EEG proxy of command-following. We show for the first time the willful modulation of the HEP in an UWS/VS patient and a locked-in syndrome patient, along with significant classification accuracies when combining the explored features. Importantly, the brain markers studied in this work provide multiple layers to explore information processing in disorders of conscious patients, and expand the framework of heart-brain interactions employed for diagnostic purposes.

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bioRxiv2022

Sleep deprivation measured by voice analysis

Sleep deprivation has an ever-increasing impact on individuals and societies. Yet, to date, there is no quick and objective test for sleep deprivation. Here, we used automated acoustic analyses of the voice to detect sleep deprivation. Building on current machine-learning approaches, we focused on interpretability by introducing two novel ideas: the use of a fully generic auditory representation as input feature space, combined with an interpretation technique based on reverse correlation. The auditory representation consisted of a spectro-temporal modulation analysis derived from neurophysiology. The interpretation method aimed to reveal the regions of the auditory representation that supported the classifiers decisions. Results showed that generic auditory features could be used to detect sleep deprivation successfully, with an accuracy comparable to state-of-the-art speech features. Furthermore, the interpretation revealed two distinct effects of sleep deprivation on the voice: a change in prosody and a change in timbre. Importantly, the relative balance of the two effects varied widely across individuals, even though the amount of sleep deprivation was controlled, thus confirming the need to characterize sleep deprivation at the individual level. Moreover, while the prosody factor correlated with subjective sleepiness reports, the timbre factor did not, consistent with the presence of both explicit and implicit consequences of sleep deprivation. Overall, the findings show that individual effects of sleep deprivation may be observed in vocal biomarkers. Future investigations correlating such markers with objective physiological measures of sleep deprivation could enable "sleep stethoscopes" for the cost-effective diagnosis of the individual effects of sleep deprivation. Author summarySleep deprivation has an ever-increasing impact on individuals and societies, from accidents to chronic conditions costing billions to health systems. Yet, to date, there is no quick and objective test for sleep deprivation. We show that sleep deprivation can be detected at the individual level with voice recordings. Importantly, we focused on interpretability, which allowed us to identify two independent effects of sleep deprivation on the voice: a change in prosody and a change in timbre. The results also revealed a striking variability in individual reactions to the same deprivation, further confirming the need to consider the effects of sleep deprivation at the individual level. Vocal markers could be correlated to specific underlying physiological factors in future studies, outlining possible cost-effective and non-invasive "sleep stethoscopes".

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bioRxiv2022

Memory loss at sleep onset

Every night, we pass through a transitory zone at the borderland between wakefulness and sleep, named the first stage of non-rapid eye movement sleep (N1). N1 sleep is associated with an increased hippocampal activity and dreamlike experiences that incorporate recent wake materials, suggesting that it may be associated with memory processing. Here, we investigated the specific contribution of N1 sleep in the processing of memory traces. Participants were asked to learn the precise locations of 48 objects on a grid and were then tested on their memory for these items before and after a 30-minute rest during which participants either stayed fully awake, transitioned toward N1 or deeper (N2) sleep. We showed that memory recall was lower (10% forgetting) after a resting period including only N1 sleep compared to N2 sleep. Furthermore, the ratio of alpha/theta power (an EEG marker of the transition towards sleep) correlated negatively with the forgetting rate when taking into account all sleepers (N1 and N2 groups combined), suggesting a physiological index for memory loss that transcends sleep stages. Our findings suggest that interrupting sleep onset at N1 may alter sleep-dependent memory consolidation and promote forgetting.

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bioRxiv2022

Pharmacological manipulations of physiological arousal and sleep-like slow waves modulate sustained attention

Sustained attention describes our ability to keep a constant focus on a given task. This ability is modulated by our physiological state of arousal. Although lapses of sustained attention have been linked with dysregulations of arousal, the underlying physiological mechanisms remain unclear. An emerging body of work proposes that the intrusion during wakefulness of sleep-like slow waves, a marker of the transition toward sleep, could mechanistically account for attentional lapses. This study aimed to expose, via pharmacological manipulations of the monoamine system, the relationship between the occurrence of sleep-like slow waves and the behavioural consequences of sustained attention failures. In a double-blind, randomised-control trial, 32 healthy human male participants received methylphenidate, atomoxetine, citalopram or placebo during four separate experimental sessions. During each session, electroencephalography (EEG) was used to measure neural activity whilst participants completed a visual task requiring sustained attention. Methylphenidate, which increases wake-promoting dopamine and noradrenaline across cortical and subcortical areas, improved behavioural performance whereas atomoxetine, which increases dopamine and noradrenaline predominantly over frontal cortices, led to more impulsive responses. Additionally, citalopram, which increases sleep-promoting serotonin, led to more missed trials. Based on EEG recording, citalopram was also associated with an increase in sleep-like slow waves. Importantly, compared to a classical marker of arousal such as alpha power, only slow waves differentially predicted both misses and faster responses in a region-specific fashion. These results suggest that a decrease in arousal can lead to local sleep intrusions during wakefulness which could be mechanistically linked to impulsivity and sluggishness. Significance StatementWe investigated whether the modulation of attention and arousal could not only share the same neuromodulatory pathways but also rely on similar neuronal mechanisms; for example, the intrusion of sleep-like activity within wakefulness. To do so, we pharmacologically manipulated noradrenaline, dopamine, and serotonin in a four-arm, randomised, placebo-controlled trial and examined the consequences on behavioural and EEG indices of attention and arousal. We showed that sleep-like slow waves can predict opposite behavioural signatures: impulsivity and sluggishness. Slow waves may be a candidate mechanism for the occurrence of attentional lapses since the relationship between slow-wave occurrence and performance is region-specific and the consequences of these local sleep intrusions are in line with the cognitive functions carried by the underlying brain regions.

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