Biology subjects

Handjaras, G.

Publications and source records attributed to Handjaras, G..

At least 19 recordsLinked to original sources

bioRxiv2026

Visual speech supports phonetic attunement in the absence of early auditory input

The first year of life is considered a sensitive period for the acquisition of phonetic categories, a hallmark of successful native language specialization. The extent to which this process depends on early auditory experience and intrinsic biological constraints remains unresolved. We measured neural encoding of continuous natural speech in hearing children (HC) and cochlear implant (CI) users with congenital or acquired deafness, contrasting children with and without access to auditory input in the first year of life. Speech encoding was present across all groups, but its specificity depended on early input: auditory phonetic features were encoded only in children exposed to speech within the first year, whereas visually discriminable phonetic features were encoded regardless of auditory deprivation. These findings show that early sensory input gates phonetic attunement; this constraint is not limited to or grounded in audition but instead reveals a sensitive period that is modality-flexible in mechanism and experience-dependent in expression.

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bioRxiv2025

Immersive NREM dreaming preserves subjective sleep depth against declining sleep pressure

Perceived sleep depth is a key determinant of subjective sleep quality, traditionally thought to reflect unconsciousness and reduced cortical activation. Here, we combined high-density EEG with a serial awakening paradigm during NREM sleep to examine its neural and experiential correlates. As expected, deeper sleep was associated with reduced cortical activation, reflected in a lower high-to-low frequency power ratio. Yet, this relationship weakened in the presence of dreaming, indicating that immersive conscious experiences can counteract the impact of cortical activation on perceived depth. Indeed, perceived sleep depth was lowest during states with a mere sense of presence and highest during immersive dreaming or deep unconsciousness. Across the night, physiological sleep pressure and subjective sleepiness declined, but perceived sleep depth rose alongside increasing dream immersiveness. These results challenge the view that deep sleep stems solely from reduced brain activity and suggest that immersive dreaming sustains perceived sleep depth as homeostatic pressure wanes.

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bioRxiv2025

The semantics of dreams

Dreams are universal yet deeply personal experiences. While memory and personal concerns influence dream content, the impact of other individual, generalizable traits remains poorly understood. To address this gap, we built a multimodal dataset including dream and wakefulness reports, alongside demographic, psychometric, cognitive, and sleep-related measures in a large adult cohort. Natural language processing characterized the semantic features that quantitatively distinguish dream from wakefulness reports, with this distinction significantly modulated by individual-specific factors. Longitudinal and cross-sample analyses further demonstrated that major external events, such as the COVID-19 pandemic, affect dream content, leaving lasting traces. Overall, the findings highlight a dynamic interplay between stable individual traits and external events in shaping dream experiences, offering novel insights into the cognitive and emotional architecture of dreaming.

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bioRxiv2025

Thalamic involvement defines distinct slow-wave subtypes in NREM sleep

Slow waves (0.5-4 Hz) are a key feature of non-rapid-eye-movement (NREM) sleep, traditionally believed to arise from neocortical circuits. However, growing evidence suggests that subcortical structures, particularly the thalamus, may play a crucial role in initiating and synchronizing slow waves. We tested the hypothesis that single slow waves may arise from distinct cortico-cortical and thalamo-cortical mechanisms using simultaneous EEG-fMRI in healthy adults. Spatial mapping based on thalamic fMRI responses revealed two types of slow waves. The first type (C1) characterized by an early thalamic fMRI-signal increase, corresponded to large, efficiently synchronized waves associated with sleep spindles and with markers of higher arousal and autonomic activation. The second type (C2) is marked by an initial negative fMRI response and corresponds to smaller slow waves potentially resulting from cortico-cortical synchronization. These waves occur more often during phases of stable NREM sleep. These findings highlight distinct slow-wave subtypes with different thalamic involvement and, potentially, synchronization mechanisms.

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bioRxiv2024

The individual determinants of morning dream recall

Evidence suggests that (almost) everyone dreams during their sleep and may actually do so for a large part of the night. Yet, dream recall shows large interindividual variability. Understanding the factors that influence dream recall is crucial for advancing our knowledge regarding dreams origin, significance, and functions. Here, we tackled this issue by prospectively collecting dream reports along with demographic information and psychometric, cognitive, actigraphic, and electroencephalographic measures in 204 healthy adults (18-70 y, 113 females). We found that attitude towards dreaming, proneness to mind wandering, and sleep patterns are associated with the probability of reporting a dream upon morning awakening. The likelihood of recalling dream content was predicted by age and vulnerability to interference. Moreover, dream recall appeared to be influenced by night-by-night changes in sleep patterns and showed seasonal fluctuations. Our results provide an account for previous observations regarding inter- and intra-individual variability in morning dream recall.

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bioRxiv2024

Resilience and vulnerability of speech neural tracking to early auditory deprivation

Infants are born with biological biases that favour language acquisition. One is the auditory systems ability to track the envelope of continuous speech, a pivotal feature for spoken language comprehension in adulthood. However, the extent to which neural speech tracking relies on postnatal auditory experience remains unknown. In this case-control study, we tested children with or without access to functional hearing in the first year of life after they received cochlear implants (CIs) for hearing restoration. We measured neural speech tracking in CI users with a congenital bilateral profound deafness (CD) or who acquired it later in development (AD; minimum auditory experience after birth 12 months), as well as in two groups of hearing controls listening to original (HC) or vocoded-speech (HC-v). Remarkably, neural speech tracking in children with CIs was unaffected by the absence of perinatal auditory experience. Regardless of deafness onset, CI users and HC exhibited a similar neural tracking magnitude at short timescales [~]50- 130 ms (P1TRF) of brain activity. However, this neural tracking phase (P1TRF) was delayed in CI users, and its timing depended on the age of hearing restoration. Conversely, at longer timescales [~]130-260 ms (N2TRF) of brain activity, speech tracking was substantially dampened in participants with CIs, thereby accounting for their comprehension deficits. Speech tracking in HC listening to vocoded-speech and in a phantom head-model with CIs suggested that neural processing differences between HC and CI children could not merely be explained by the degraded acoustic stimulation, nor by electrical artifacts of the implants. These findings highlight (i) the resilience of sensory components of neural speech tracking to the lack of hearing in the first year of life, (ii) the crucial role played when hearing restoration takes place in mitigating the impact of atypical auditory experience, (iii) the vulnerability of higher hierarchical levels of speech processing in CI users.

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bioRxiv2024

The impact of face masks on face-to-face neural tracking of speech: auditory and visual obstacles

Face masks provide fundamental protection against the transmission of respiratory viruses but hamper communication. We estimated auditory and visual obstacles generated by face masks on communication by measuring the neural tracking of face-to-face speech. To this end, we recorded the EEG while participants were exposed to naturalistic audio-visual speech, embedded in multi-talker noise, in three contexts: (i) no-mask (audio-visual information was fully available), (ii) virtual mask (occluded lips, but intact audio), and (iii) real mask (occluded lips and degraded audio). The neural tracking of lip movements and the sound envelope of speech was measured through backward modeling, that is, by reconstructing stimulus properties from neural activity. Behaviorally, face masks increased listening -phonological-errors in speech content retrieval and perceived listening difficulty. At the neural level, we observed that the occlusion of the mouth abolished lip tracking and dampened neural tracking of the speech envelope at the earliest processing stages. Degraded acoustic information due to face mask filtering altered neural tracking at later processing stages instead. Finally, a consistent link emerged between the increment of listening perceived difficulty and the drop in reconstruction performance of speech envelope when attending to a speaker wearing a face mask. Results clearly dissociated the visual and auditory impacts of face masks on face-to-face neural tracking of speech. While face masks hampered the ability to predict and integrate audio-visual speech, the auditory filter generated by face masks impacted the neural processing stages typically associated with auditory selective attention. The link between perceived difficulty and neural tracking drop provided evidence of a major impact of face masks on the metacognitive levels subtending speech processing.

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bioRxiv2023

Abstract, modality-specific and experience-dependent coding of affect in the human brain

Emotion and perception are tightly intertwined, as affective experiences often arise from the appraisal of sensory information. Nonetheless, whether the brain encodes emotional instances using a sensory-specific code or in a more abstract manner is unclear. Here, we answer this question by measuring the association between emotion ratings collected during a unisensory or multisensory presentation of a full-length movie and brain activity recorded in typically-developed, congenitally blind and congenitally deaf participants. Emotional instances are encoded in a vast network encompassing sensory, prefrontal, and temporal cortices. Within this network, the ventromedial prefrontal cortex stores a categorical representation of emotion independent of modality and experience, and the posterior superior temporal cortex maps valence using an abstract code. Sensory experience more than modality impacts how the brain organizes emotional information outside supramodal regions, suggesting the existence of a scaffold for the representation of emotional states where sensory inputs during development shape its functioning.

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bioRxiv2023

Brain structure reflects empathy and psychopathy in incarcerated males

BackgroundReduced empathy is a hallmark of individuals with high (i.e., clinical) levels of psychopathy, who are overrepresented among incarcerated men. Yet, a comprehensive, well-powered mapping of cortical structure in relation to empathy and psychopathy is still lacking. MethodsIn 804 incarcerated adult men, we administered the Perspective Taking (IRI-PT) and Empathic Concern (IRI-EC) subscales of the Interpersonal Reactivity Index, the Psychopathy Checklist-Revised (PCL-R; with Interpersonal/Affective [F1] and Lifestyle/Antisocial [F2] factors), and T1-weighted MRI to quantify cortical thickness (CT), surface area (SA), and structural-covariance gradients. ResultsPCL-R F1 was uniquely negatively related to IRI-EC, while PCL-R F2 was uniquely negatively related to IRI-PT. Cortical structure was not related to the IRI subscales. In contrast, CT was related to PCL-R F1 (mostly positively), SA was related to both PCL-R factors (only positively), and both cortical indices demonstrated out-of-sample predictive utility for PCL-R F1. Compared to low-psychopathy men, high-psychopathy men had uniquely lower IRI-EC scores and increased SA (but not CT); across the cortex, effect sizes were largest in the paralimbic class and somatomotor network, while meta-analytic task-based activations further highlighted spatial overlap with (social-)affective/sensory regions. Finally, the total sample revealed canonical anterior-posterior structural-covariance gradients. In high-psychopathy men, the gradient of CT (but not SA) was globally compressed. ConclusionsHigh-psychopathy men had reduced empathic concern, increased SA, and a compressed macroscale organization of CT, suggesting specific co-occurring alterations in empathy and cortical structure. Future work should build upon these novel insights in both the general and incarcerated populations to inform the treatment of psychopathy.

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bioRxiv2023

Maturation-dependent changes in cortical and thalamic activity during slow waves of light sleep: insights from a combined EEG-fMRI study

INTRODUCTIONStudies using scalp EEG have shown that slow waves (0.5-4 Hz), the most prominent hallmark of NREM sleep, undergo relevant changes from childhood to adulthood, mirroring brain structural modifications and the acquisition of cognitive skills. Here we used simultaneous EEG-fMRI to investigate the cortical and subcortical correlates of slow waves in school-age children and determine their relative developmental changes. METHODSWe analyzed data from 14 school-age children with self-limited focal epilepsy of childhood who fell asleep during EEG-fMRI recordings. Brain regions associated with slow-wave occurrence were identified using a voxel-wise regression that also modeled interictal epileptic discharges and sleep spindles. At the group level, a mixed-effects linear model was used. The results were qualitatively compared with those obtained from 2 adolescents with epilepsy and 17 healthy adults. RESULTSSlow waves were associated with hemodynamic-signal decreases in bilateral somatomotor areas. Such changes extended more posteriorly relative to those in adults. Moreover, the involvement of areas belonging to the default mode network changes as a function of age. No significant hemodynamic responses were observed in subcortical structures. However, we identified a significant correlation between age and thalamic hemodynamic changes. CONCLUSIONSPresent findings indicate that the somatomotor cortex may have a key role in slow-wave expression throughout the lifespan. At the same time, they are consistent with a posterior-to-anterior shift in slow-wave distribution mirroring brain maturational changes. Finally, our results suggest that slow-wave changes may not reflect only neocortical modifications but also the maturation of subcortical structures, including the thalamus. Statement of significanceLow spatial resolution of conventional EEG has widely limited the possibility of accurately determining in humans the role of different brain structures in the expression of sleep slow waves throughout development. Here, for the first time, we took advantage of a simultaneous EEG-fMRI approach to accurately describe the cortical and subcortical hemodynamic correlates of sleep slow waves in a sample of 14 school-aged children. In order to elucidate age-dependent changes, we qualitatively compared present findings with those previously obtained in a group of adults. Overall our results have important implications for the understanding of how cortico-cortical and subcortico-cortical interactions shape sleep slow waves across development.

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bioRxiv2022

A visual representation of the hand in the resting somatomotor regions of the human brain

Hands are regularly in sight in everyday life. This visibility affects motor control, perception, and attention, as visual information is integrated into an internal model of sensorimotor control. Spontaneous brain activity, i.e., ongoing activity in the absence of an active task (rest), is correlated among somatomotor regions that are jointly activated during motor tasks1. Moreover, recent studies suggest that spontaneous activity patterns do not only replay at rest task activation patterns, but also maintain a model of the statistical regularities (priors) of the body and environment, which may be used to predict upcoming behavior2-4. Here we test whether spontaneous activity in the human somatomotor cortex is modulated by visual stimuli that display hands vs. non-hand stimuli, and by the use/action they represent. We analyzed activity with fMRI and multivariate pattern analysis to examine the similarity between spontaneous (rest) activity patterns and task-evoked patterns to the presentation of natural hands, robot hands, gloves, or control stimuli (food). In the left somatomotor cortex we observed a stronger (multi-voxel) spatial correlation between resting-state activity and natural hand picture patterns, as compared to other stimuli. A trend analysis showed that task-rest pattern similarity was influenced by inferred visual and motor attributes (i.e., correlation for hand>robot>glove>food). We did not observe any task-rest similarity in the visual cortex. We conclude that somatomotor brain regions code at rest for visual representations of hand stimuli and their inferred use.

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bioRxiv2022

A modality independent proto-organization of human multisensory areas

The processing of multisensory information is based upon the capacity of brain regions, such as the superior temporal cortex, to combine information across modalities. However, it is still unclear whether the representation of coherent auditory and visual events does require any prior audiovisual experience to develop and function. In three fMRI experiments, intersubject correlation analysis measured brain synchronization during the presentation of an audiovisual, audio-only or video-only versions of the same narrative in distinct groups of sensory-deprived (congenitally blind and deaf) and typically-developed individuals. The superior temporal cortex synchronized across auditory and visual conditions, even in sensory-deprived individuals who lack any audiovisual experience. This synchronization was primarily mediated by low-level perceptual features and relied on a similar modality-independent topographical organization of temporal dynamics. The human superior temporal cortex is naturally endowed with a functional scaffolding to yield a common representation across multisensory events.

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bioRxiv2020

Intersubject brain connectivity dynamics encode the stream of affect at multiple timescales

In everyday life the stream of affect results from the interaction between past experiences, expectations, and the unfolding of events. How the brain represents the relationship between time and affect has been hardly explored, as it requires modeling the complexity of everyday life in the laboratory setting. Movies condense into hours a multitude of emotional responses, synchronized across subjects and characterized by temporal dynamics alike real-world experiences. Here, we use time-varying intersubject brain synchronization and real-time behavioral reports to test whether connectivity dynamics track changes in affect during movie watching. Results show that polarity and intensity of experiences relate to connectivity of the default mode and control networks and converge in the right temporo-parietal cortex. We validate these results in two experiments including four independent samples, two movies, and alternative analysis workflows. Lastly, we reveal chronotopic connectivity maps within temporo-parietal and prefrontal cortex, where adjacent areas preferentially encode affect at specific timescales.

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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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bioRxiv2020

Auditory features modelling demonstrates sound envelope representation in striate cortex

The striate cortex is no longer considered exclusively visual in its function. Proofs that its activity is modulated by acoustic inputs have accrued. By employing category-based and feature modeling approaches, here we characterized V1 activity (in absence of retinal input) during the processing of natural and synthetically derived sounds. First, we showed that distinct sound categories could be dissociated by the analysis of V1 multivoxel response patterns. Hence, we assessed whether a hallmark of sound neural representations is mapped in V1. In each sound category, we modeled sound envelopes and assessed whether these were represented at the single-voxel level in the striate cortex and, as a control, in the temporal cortex. The hierarchical organization of sound categories allowed to exert control over dimensions that could spuriously lead to sound envelope V1 mapping. Variations of sound amplitude over time were successfully decoded in V1 regardless of the category class. Results confirm that the human striate cortex receives acoustic category-based input and demonstrate that V1 is a genuine locus of sound envelope representation.

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bioRxiv2019

Shape coding in occipito-temporal cortex relies on object silhouette, curvature and medial-axis

Object recognition relies on different transformations of the retinal input, carried out by the visual system, that range from local contrast to object shape and category. While some of those transformations are thought to occur at specific stages of the visual hierarchy, the features they represent are correlated (e.g., object shape and identity) and selectivity for the same feature overlaps in many brain regions. This may be explained either by collinearity across representations, or may instead reflect the coding of multiple dimensions by the same cortical population. Moreover, orthogonal and shared components may differently impact on distinctive stages of the visual hierarchy. We recorded functional MRI (fMRI) activity while participants passively attended to object images and employed a statistical approach that partitioned orthogonal and shared object representations to reveal their relative impact on brain processing. Orthogonal shape representations (silhouette, curvature and medial-axis) independently explained distinct and overlapping clusters of selectivity in occitotemporal (OTC) and parietal cortex. Moreover, we show that the relevance of shared representations linearly increases moving from posterior to anterior regions. These results indicate that the visual cortex encodes shared relations between different features in a topographic fashion and that object shape is encoded along different dimensions, each representing orthogonal features. New & NoteworthyThere are several possible ways of characterizing the shape of an object. Which shape description better describes our brain responses while we passively perceive objects? Here, we employed three competing shape models to explain brain representations when viewing real objects. We found that object shape is encoded in a multi-dimensional fashion and thus defined by the interaction of multiple features.

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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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bioRxiv2018

Emotionotopy: Gradients encode emotion dimensions in right temporo-parietal territories

Humans use emotions to decipher complex cascades of internal events. However, which mechanisms link descriptions of affective states to brain activity is unclear, with evidence supporting either local or distributed processing. A biologically favorable alternative is provided by the notion of gradient, which postulates the isomorphism between functional representations of stimulus features and cortical distance. Here, we use fMRI activity evoked by an emotionally charged movie and continuous ratings of the perceived emotion intensity to reveal the topographic organization of affective states. Results show that three orthogonal and spatially overlapping gradients encode the polarity, complexity and intensity of emotional experiences in right temporo-parietal territories. The spatial arrangement of these gradients allows the brain to map a variety of affective states within a single patch of cortex. As this organization resembles how sensory regions represent psychophysical properties (e.g., retinotopy), we propose emotionotopy as a principle of emotion coding.

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