Biology subjects

Siclari, F.

Publications and source records attributed to Siclari, F..

11 recordsLinked to original sources

bioRxiv2025

Aperiodic EEG Activity Provides a Linear, Bidirectional, and Spatially Uniform Marker of Subjective and Objective Vigilance in Humans, Both Within and Across States

1Vigilance is increasingly conceived as a continuum, ranging from full alertness to deep sleep. Despite its fundamental role in cognition, behaviour, and health, reliable physiological markers of vigilance remain limited, and clinical assessments often rely on subjective or time-consuming evaluations. Traditionally, vigilance has been estimated through visual inspection of the electroencephalogram (EEG), identifying recognizable oscillatory patterns like rapid, wakefulness-defining alpha waves ([~]10 Hz) and large slow waves ([~]1 Hz) which typify sleep. However, these oscillatory features often appear only intermittently and follow complex, non-linear trajectories across time, space, and frequency, limiting their utility for automated, continuous tracking of vigilance. Recent research has shifted attention to the non-oscillatory, or aperiodic, component of the EEG, which may follow simpler dynamics and offer a more robust index of brain state. Yet most studies often continue to use narrowly defined, discrete vigilance states and transitions in only one direction (e.g., from wakefulness to sleep), without jointly examining oscillatory and aperiodic activity. Here, we address these key gaps by evaluating the capacity of both oscillatory and aperiodic features of EEG power spectra, derived from high-density recordings, to predict vigilance as a continuous variable. Across three independent datasets, we consistently show that although oscillatory features reliably track changes in vigilance, they are unequivocally outperformed by aperiodic activity. Aperiodic features demonstrate a stronger, more linear, and spatially consistent relationship with both objective and subjective indices of vigilance, offering a more robust and scalable physiological marker of this fundamental feature of the brain. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=173 SRC="FIGDIR/small/673229v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1c66d88org.highwire.dtl.DTLVardef@4126b0org.highwire.dtl.DTLVardef@152f10borg.highwire.dtl.DTLVardef@4f413f_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Multisensory integration in Peripersonal Space indexes consciousness states in sleep and disorders of consciousness

Conscious experience encompasses not only the awareness of external objects, but also a phenomenal representation of the embodied subject of the experience. The latter is mediated by the integration of multisensory stimuli between the body and the environment, a process mediated by the Peripersonal Space (PPS) system. Here we thus tested the hypothesis that a neural marker of PPS representation may index the presence of conscious experience. Using high-density EEG in awake participants, we identified a "PPS index", characterized by high-beta oscillations in centroparietal regions during the integration of audiotactile stimuli presented near versus far from the body. We then examined this marker across two models of altered consciousness, i.e., sleep and disorders of consciousness. The PPS index persisted during dreaming and waking conscious states but was absent during dreamless, unconscious states. Moreover, the same index predicted behavioural measures of consciousness and clinical outcome in patients recovering from disorders of consciousness. These results suggest that multisensory integration within the PPS is tightly linked to the presence of conscious experience.

neuroscience↗

bioRxiv2024

Consciousness in Non-REM parasomnia episodes

Sleepwalking and related parasomnias are thought to result from incomplete awakenings out of Non rapid eye movement (Non-REM) sleep. Non-REM parasomnia behaviors have been described as unconscious and automatic, or related to vivid, dream-like conscious experiences. Similarly, some observations have suggested that patients are unresponsive during episodes, while others that they can interact with their surroundings. To better grasp and characterize the full spectrum of consciousness and environmental disconnection associated with behavioral episodes, 35 adult patients with Non-REM sleep parasomnias were interviewed in-depth about their experiences. The level of consciousness during parasomnia episodes was reported to be variable both within and between individuals, ranging from minimal or absent consciousness and largely automatic behaviors (frequently/always present in 36% of patients) to preserved conscious experiences characterized by delusional thinking of varying degrees of specificity (65%), often about impending danger, variably formed, uni- or multisensory hallucinations (53%), impaired insight (77%), negative emotions (75%) and variable, but often pronounced amnesia (30%). Patients described their experiences as a dream scene during which they felt awake ( awake dreaming). Surroundings were either realistically perceived, misinterpreted (in the form of perceptual illusions or misidentifications of people) or entirely hallucinated as a function of the prevailing delusion. These observations suggest that the level of consciousness and sensory disconnection in Non-REM parasomnias is variable and graded. In their full-fledged expression, Non-REM parasomnia experiences feature several core features of dreams. They therefore represent a valuable model for the study of consciousness, sleep-related sensory disconnection and dreaming.

neuroscience↗

bioRxiv2024

Cardiovascular responses to natural and auditory evoked slow waves predict post-sleep cardiac function

The interplay between slow-wave sleep and cardiovascular health is increasingly recognized. Our prior research showed that auditory-enhanced slow waves can boost cardiac function, yet the mechanisms behind this remain unclear. Advancing these findings, our current analysis dissected the effects of two slow wave types on cardiovascular function, using data from 18 middle-aged men across three nights. We found that the strength of heart rate and blood pressure responses concurrent with slow waves predicts cardiac function post-sleep. Notably, we identified that highly synchronized type I slow waves, as opposed to lower-amplitude type II slow waves, primarily co-occur with these cardiovascular pulsations. While auditory stimulation enhances both types of slow waves, they exhibit distinct temporal dynamics, pointing to different underlying biological mechanisms. This study crucially addresses how distinct slow wave types can affect cardiovascular function, implying that targeted slow wave stimulation could be a strategic approach to improve heart health.

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bioRxiv2023

Non-REM parasomnia experiences share EEG correlates with dreams

Sleepwalking and related parasomnias result from sudden and incomplete awakenings out of slow wave sleep. Clinical observations suggest that behavioral episodes can occur without consciousness and recollection, or in relation to dream-like experiences. To understand what accounts for these differences in consciousness and amnesia, we recorded parasomnia episodes with high-density EEG and interviewed participants immediately afterwards. Compared to reports of unconsciousness (19%), reports of conscious experience (81%) were preceded, during prior sleep, by high-amplitude slow waves in anterior cortical regions and an activation of posterior cortical regions. Reduced posterior slow wave activity was also present during the episode when patients displayed elaborate behaviours in relation to dream-like scenarios. Amnesia for the experience (25%) was modulated by right medial temporal activation during prior sleep and fronto-parietal slow wave activity during the episode. Thus, the neural correlates of parasomnia experiences are similar to those previously reported for dreams and therefore likely reflect core physiological processes involved in sleep consciousness.

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bioRxiv2021

The determinants of the subjective perception of sleep: insights from a high-density EEG study with serial awakenings

What accounts for the feeling of being deeply asleep? Standard sleep recordings only incompletely reflect subjective aspects of sleep and some individuals with so-called sleep misperception frequently feel awake although sleep recordings indicate clear-cut sleep. To identify the determinants of the subjective perception of sleep, we performed 787 awakenings in 20 good sleepers and 10 individuals with sleep misperception and interviewed them about their subjective sleep depth while they underwent high-density EEG sleep recordings. Surprisingly, in good sleepers, sleep was subjectively lightest in the first two hours of Non-rapid eye movement (NREM) sleep, generally considered the deepest sleep, and deepest in rapid eye movement (REM) sleep. Compared to good sleepers, sleep misperceptors felt more frequently awake during sleep and reported lighter REM sleep. At the EEG level, spatially widespread high-frequency power was inversely related to subjective sleep depth in NREM sleep in both groups and in REM sleep in misperceptors. Subjective sleep depth positively correlated with dream-like qualities of reports of mental activity. These findings challenge the widely held notion that slow wave sleep best accounts for feeling deeply asleep. Instead, they indicate that subjective sleep depth is inversely related to a neurophysiological process that predominates in early NREM sleep, becomes quiescent in REM sleep and is reflected in high-frequency EEG-activity. In sleep misperceptors, this process is more frequently active, more spatially widespread, and abnormally persists into REM sleep. These findings help identify the neuromodulatory systems involved in subjective sleep depth and are relevant for studies aiming to improve subjective sleep quality.

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bioRxiv2020

Cortical and subcortical hemodynamic changes during human sleep slow waves

EEG slow waves, the hallmarks of NREM sleep, are closely linked to the restorative function of sleep and their regional cortical distribution reflects plasticity- and learning-related processes. Here we took advantage of simultaneous EEG-fMRI recordings to map cortical and subcortical hemodynamic (BOLD) fluctuations time-locked to sleep slow waves. Recordings were performed in twenty healthy adults during an afternoon nap. Slow waves were associated with BOLD-signal increases in the brainstem and in portions of thalamus and cerebellum characterized by preferential functional connectivity with limbic and somatomotor areas, respectively. At the cortical level, significant BOLD-signal decreases were found in several areas, including insula and somatomotor cortex, and were preceded by slow signal increases that peaked around slow-wave onset. EEG slow waves and BOLD fluctuations showed similar cortical propagation patterns, from centro-frontal to temporo-occipital cortices. These regional patterns of hemodynamic-electrical coupling are consistent with theoretical accounts of the functions of sleep slow waves.

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bioRxiv2019

Integrity of corpus callosum is essential for the cross-hemispheric propagation of sleep slow waves: a high-density EEG study in split-brain patients

The slow waves of NREM-sleep (0.5-4Hz) reflect experience-dependent plasticity and play a direct role in the restorative functions of sleep. Importantly, slow waves behave as traveling waves and their propagation is assumed to reflect the structural properties of white matter connections. Based on this assumption, the corpus callosum (CC) may represent the main responsible for cross-hemispheric slow wave propagation. To verify this hypothesis, here we studied a group of patients who underwent total callosotomy due to drug-resistant epilepsy. Overnight high-density (hd)-EEG recordings (256 electrodes) were performed in five totally callosotomized in-patients (CP; 40-53y, 2F), in three control non-callosotomized neurological in-patients (NP; 44-66y, 2F, 1M epileptic), and in an additional sample of 24 healthy adult subjects (HS; 20-47y, 13F). Data were inspected to select NREM-sleep epochs and artefactual or non-physiological activity was rejected. Slow waves were detected using an automated algorithm and their properties and propagation patterns were computed. For each slow wave parameter and for each patient, the relative z-score and the corresponding p-value were calculated with respect to the distribution represented by the HS-group. Group differences were considered significant only when a Bonferroni corrected P < 0.05 was observed in all the CP and in none of the NP. A regression-based adjustment was used to exclude potential confounding effects of age. Slow wave density, amplitude, slope and propagation speed did not differ across CP and HS. In all CP slow waves displayed a significantly reduced probability of cross-hemispheric propagation and a stronger inter-hemispheric asymmetry. Moreover, we found that the incidence of large slow waves tended to differ across hemispheres within individual NREM epochs, with a relative predominance of the right over the left hemisphere in both CP and HS. The absolute magnitude of this inter-hemispheric difference was significantly greater in CP relative to HS. This effect did not depend on differences in slow wave origin within each hemisphere across groups. Present results indicate that the integrity of the CC is essential for the cross-hemispheric traveling of sleep slow waves, supporting the assumption of a direct relationship between white matter structural integrity and cross-hemispheric slow wave propagation. Our findings also imply a prominent role of cortico-cortical connections, rather than cortico-subcortico-cortical loops, in slow wave cross-hemispheric synchronization. Finally, this data indicate that the lack of the CC does not lead to differences in sleep depth, in terms of slow wave generation/origin, across brain hemispheres.

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bioRxiv2019

Visual imagery and visual perception induce similar changes in occipital slow waves of sleep

Previous studies have shown that regional slow wave activity (SWA) during NREM-sleep is modulated by prior experience and learning. While this effect has been convincingly demonstrated for the sensorimotor domain, attempts to extend these findings to the visual system have provided mixed results. Here we asked whether depriving subjects of external visual stimuli during daytime would lead to regional changes in slow waves during sleep and whether the degree of internal visual stimulation (spontaneous imagery) would influence such changes. In two 8h-long sessions spaced one-week apart, twelve healthy volunteers either were blindfolded while listening to audiobooks or watched movies (control condition), after which their sleep was recorded with high-density EEG. We found that during NREM-sleep the number of small, local slow waves in the occipital cortex decreased after listening with blindfolding relative to movie watching in a way that depended on the degree of visual imagery subjects reported during blindfolding: subjects with low visual imagery showed a significant reduction of occipital sleep slow waves, while those who reported a high degree of visual imagery did not. We also found a positive relationship between the reliance on visual imagery during blindfolding and audiobook listening and the degree of correlation in sleep SWA between visual areas and language-related areas. These preliminary results demonstrate that short-term alterations in visual experience may trigger slow wave changes in cortical visual areas. Furthermore, they suggest that plasticity-related EEG changes during sleep may reflect externally induced ( bottom-up) visual experiences, as well as internally generated ( top-down) processes.

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bioRxiv2018

EEG functional connectivity metrics wPLI and wSMI account for distinct types of brain functional interactions

Functional connectivity (FC) estimation methods are extensively used in neuroimaging to measure brain inter-regional interactions. The weighted Phase Lag Index (wPLI) and the weighted Symbolic Mutual Information (wSMI) represent relatively robust exemplars of spectral (wPLI) and information-theoretic (wSMI) connectivity measures that recently gained increased popularity due to their relative immunity to volume conduction. wPLI and wSMI are posited to have different sensitivity to linear and nonlinear relationships between neural sources, but their performance has never been directly compared. Here, using simulated high-density (hd-)EEG data, we evaluated the accuracy of these two metrics for detecting distinct types of regional interdependencies characterised by different combinations of linear and nonlinear components. Our results demonstrate that while wPLI performs generally better at detecting functional couplings presenting a mixture of linear and nonlinear interdependencies, only wSMI is able to detect exclusively nonlinear interaction dynamics. To evaluate the potential impact of these differences on real experimental data, we computed wPLI and wSMI connectivity in hd-EEG recordings of 12 healthy adults obtained in wakefulness and deep (N3-)sleep. While both wPLI and wSMI revealed a relative decrease in alpha-connectivity during sleep relative to wakefulness, only wSMI identified a relative increase in theta-connectivity, while wPLI detected an increase in delta-connectivity, likely reflecting the occurrence of traveling slow waves. Overall, our findings indicate that wPLI and wSMI provide distinct but complementary information about functional brain connectivity, and that their combined use could advance our knowledge of neural interactions underlying different behavioural states.

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bioRxiv2018

Regional low-frequency oscillations in human rapid-eye movement sleep

Although the EEG slow wave of sleep is typically considered to be a hallmark of Non Rapid Eye Movement (NREM) sleep, recent work in mice has shown that slow waves can also occur in REM sleep. Here we investigated the presence and cortical distribution of low-frequency (1-4 Hz) oscillations in human REM sleep by analyzing high-density EEG sleep recordings obtained in 28 healthy subjects. We identified two clusters of low-frequency oscillations with distinctive properties: 1) a fronto-central cluster characterized by [~]2.5-3.0 Hz, relatively large, notched delta waves (so-called sawtooth waves) that tended to occur in bursts, were associated with increased gamma activity and rapid eye movements, and upon source modeling, displayed an occipito-temporal and a fronto-central component; and 2) a medial occipital cluster characterized by more isolated, slower (<2 Hz) and smaller waves that were not associated with rapid eye movements, displayed a negative correlation with gamma activity and were also found in NREM sleep. Thus, low-frequency oscillations are an integral part of REM sleep in humans, and the two identified subtypes (sawtooth and medial-occipital slow waves) may reflect distinct generation mechanisms and functional roles. Sawtooth waves, which are exclusive to REM sleep, share many characteristics with ponto-geniculo-occipital (PGO) waves described in animals and may represent the human equivalent or a closely related event while medio-occipital slow waves appear similar to NREM sleep slow waves.

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