Biology subjects

Sartori, I.

Publications and source records attributed to Sartori, I..

10 recordsLinked to original sources

bioRxiv2026

Simultaneous recordings link intracranial and scalp correlates of somatosensory awareness in humans

The electrophysiological events underlying the conscious perception of touch in humans remain elusive. Scalp-EEG studies have identified a negative deflection peaking 120-200 ms after stimulus onset, known as the N140. This component, recently reinterpreted as the somatosensory awareness negativity (N140/SAN), has been proposed as a putative marker of tactile awareness, but its underlying neuronal dynamics are still unknown. Intracranial studies have shown that responses to median nerve stimulation include, after an initial phasic activation mainly localized to primary somatosensory cortices, a predominantly insulo-opercular tonic broadband high-frequency activity (BHA; 50-150 Hz) that has been linked to tactile awareness. Yet these scalp and intracranial signatures have never been directly linked. Using simultaneous high-density scalp EEG and intracranial EEG recordings, we show that the N140/SAN is the scalp manifestation of the insulo-opercular local field potential that follows the BHA response to stimulation. By bridging invasive and non-invasive recordings our results identify the neural origins of the N140/SAN and connect scalp and intracranial correlates of somatosensory awareness.

neuroscience↗

bioRxiv2026

Behavioral Relevance Coding in Human Area 46 Precedes Selective Motor Activation to Action Targets

The lateral prefrontal cortex (LPFC) actively contributes to the adaptive control of goal-directed behavior. Evidence suggests that the LPFC encodes the behavioral relevance of stimuli, distinguishing action targets from irrelevant objects; however, how this selectivity emerges over time and integrates within large-scale cortical dynamics underlying action preparation remains unclear. We recorded stereo-electroencephalography (sEEG) activity from 43 patients affected by drug-resistant epilepsy while they prepared to grasp an object and compared it with passive observation of the same object. Gamma-band responses were used to characterize cortical responsiveness and to track the spatiotemporal propagation of activity during action preparation. Neural activity first emerged in the occipitotemporal cortex in both experimental conditions and then progressed along two parallel pathways: an intraparietal and a prefrontal one. The intraparietal pathway showed highly similar dynamics during both action preparation and passive observation, suggesting largely intention-independent visuospatial processing. In contrast, the prefrontal pathway exhibited progressively stronger selectivity for behaviorally relevant objects as activity advanced rostrally. Within this pathway, area 46 exhibited sustained responses selectively associated with action-relevant objects, preceding the similarly selective engagement of premotor and motor regions. Overall, our findings identify area 46 as a key node in whole-brain dynamics that orchestrates action preparation by integrating object relevance into executive control signals guiding premotor and motor engagement. NEW & NOTEWORTHYFilling a critical gap in system-level accounts of LPFC function, whole-brain recordings reveal that area 46 selectively codes object-related information relevant for action and gates motor region activity only when the object represents a true action target.

neuroscience↗

bioRxiv2025

Transcranial magnetic vs intracranial electric stimulation: a direct comparison of their effects via scalp EEG recordings

BackgroundSingle-pulse Transcranial Magnetic Stimulation (TMS) and Intracranial Electrical Stimulation (IES) are widely used to probe cortical excitability and connectivity, but their electrophysiological effects have never been compared. ObjectiveThis study aims to fill this gap by using high-density scalp electroencephalogram (hd-EEG) as a common read-out to compare human brain responses to TMS and IES. MethodsThe dataset includes TMS-evoked potentials (TEPs) acquired from healthy subjects (n=22) and IES-evoked potentials (IEPs) recorded from drug-resistant epileptic patients (n=31) during wakefulness. In a subset of subjects TEPs (n=12) and IEPs (n=13) were also recorded during NREM sleep. Amplitude, spectral, and spatiotemporal features of TMS and IES responses, as well as their estimated electrical fields, were compared. ResultsWe observed marked differences between TMS and IES responses. During wakefulness, IEPs are considerably larger, slower and associated with a suppression of cortical activity, whereas TEPs are characterized by multiple waves of recurrent activation. These differences are attenuated during NREM, during which both TMS and IES elicit large EEG responses associated with a prominent suppression of cortical activity. At the global level, the spatiotemporal complexity of the responses to both TMS and IES decreases consistently following the transition from wakefulness to NREM sleep. ConclusionDespite the limitations due to different subject populations (healthy vs pathological), our findings provide a first reference to parallel non-invasive and invasive brain stimulation and to interpret their differential effects. They also offer important insight on how cortical responsiveness is shaped by inhibition and adaptation mechanisms depending on input parameters and brain states. Highlights- IES evokes higher signal-to-noise EEG responses than TMS. - IES responses are larger, slower, and lead to cortical suppression. - TMS elicits faster recurrent waves, with no suppression during wakefulness. - Both TMS and IES converge to similar patterns during NREM sleep.

neuroscience↗

bioRxiv2025

Hemispherotomy: a cortical island of sleep-like activity in awake humans

Hemispherotomy is a neurosurgical procedure for treating refractory epilepsy, which entails disconnecting a significant portion of the cortex, potentially encompassing an entire hemisphere, from its cortical and subcortical connections. While this intervention prevents the spread of seizures, it raises important questions. Given the complete isolation from sensory-motor pathways, it remains unclear whether the disconnected cortex retains any form of inaccessible awareness. More broadly, the activity patterns that large portions of the deafferented cortex can sustain in awake humans remain poorly understood. We address these questions by exploring for the first time the electrophysiological state of the isolated cortex before and after surgery in ten awake pediatric patients. Post-surgery, the isolated cortex exhibited prominent slow oscillations (<2 Hz) and a broad-band shift in power spectral density from high to low frequencies. This resulted in a marked decrease of the spectral exponent, a validated consciousness marker, indicating broad-band slowing characteristic of unconscious states. When compared with a reference pediatric sample across the sleep-wake cycle, the spectral exponent of the contralateral cortex aligned with wakefulness, whereas that of the isolated cortex was consistent with deep NREM sleep. However, spindles did not emerge in the isolated cortex due to the lack of subcortical inputs, constituting a fundamental difference from physiological sleep. These findings demonstrate a unihemispheric sleep-like state during wakefulness, challenging the possibility that hemispherotomy might lead to inaccessible "islands of awareness." Moreover, the persistence of sleep-like patterns years after disconnection provides unique insights into the electrophysiological effects of disconnections in the human brain.

neuroscience↗

bioRxiv2024

Thalamic feedback shapes brain responses evoked by cortical stimulation in mice and humans

Cortical stimulation with single pulses is a common technique in clinical practice and research. However, we still do not understand the extent to which it engages subcortical circuits which contribute to the associated evoked potentials (EPs). Here we find that cortical stimulation generates remarkably similar EPs in humans and mice, with a late component similarly modulated by the subjects behavioral state. We optogenetically dissect the underlying circuit in mice, demonstrating that the late component of these EPs is caused by a thalamic hyperpolarization and rebound. The magnitude of this late component correlates with the bursting frequency and synchronicity of thalamic neurons, modulated by the subjects behavioral state. A simulation of the thalamo-cortical circuit highlights that both intrinsic thalamic currents as well as cortical and thalamic GABAergic neurons contribute to this response profile. We conclude that the cortical stimulation engages cortico-thalamo-cortical circuits highly preserved across different species and stimulation modalities. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=140 SRC="FIGDIR/small/578243v2_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@cae203org.highwire.dtl.DTLVardef@1bc5223org.highwire.dtl.DTLVardef@b48e43org.highwire.dtl.DTLVardef@1e7fe34_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

An in-vivo validation of ESI methods with focal sources

Electrical source imaging (ESI) aims at reconstructing the electrical brain activity from measurements of the electric field on the scalp. Even though the localization of single focal sources should be relatively straightforward, different methods provide diverse solutions due to the different underlying assumptions. Furthermore, their input parameter(s) further affects the solution provided by each method, making localization even more challenging. In addition, validations and comparisons are typically performed either on synthetic data or through post-operative outcomes, in both cases with considerable limitations. We use an in-vivo high-density EEG dataset recorded during intracranial single pulse electrical stimulation, in which the true sources are substantially dipolar and their locations are known. We compare ten different ESI methods under multiple choices of input parameters, to assess the accuracy of the best reconstruction, as well as the impact of the parameters on the localization performance. Best reconstructions often fall within 1 cm from the true source, with more accurate methods outperforming less accurate ones by 1 cm, on average. Expectedly, dipolar methods tend to outperform distributed methods. Sensitivity to input parameters varies widely between methods. Depth weighting played no role for three out of six methods implementing it. In terms of regularization parameters, for several distributed methods SNR=1 unexpectedly turned out to be the best choice among the tested ones. Our data show similar levels of accuracy of ESI techniques when applied to "conventional" (32 channels) and dense (64, 128, 256 channels) EEG recordings. Overall findings reinforce the importance that ESI may have in the clinical context, especially when applied to identify the surgical target in potential candidates for epilepsy surgery.

neuroscience↗

bioRxiv2020

Simultaneous human intracerebral stimulation and HD-EEG: ground-truth for source localization methods

Precisely localizing the sources of brain activity as recorded by EEG is a fundamental procedure and a major challenge for both research and clinical practice. Even though many methods and algorithms have been proposed, their relative advantages and limitations are still not well established. Moreover, these methods involve tuning multiple parameters, for which no principled way of selection exists yet. These uncertainties are emphasized due to the lack of ground-truth for their validation and testing. Here we provide the first open dataset that comprises EEG recorded electrical activity originating from precisely known locations inside the brain of living humans. High-density EEG was recorded as single-pulse biphasic currents were delivered at intensities ranging from 0.1 to 5 mA through stereotactically implanted electrodes in diverse brain regions during pre-surgical evaluation of patients with drug-resistant epilepsy. The uses of this dataset range from the estimation of in vivo tissue conductivity to the development, validation and testing of forward and inverse solution methods.

neuroscience↗

bioRxiv2020

Stereo-EEG reveals rich cortical dynamics in humans coping with difficult action discrimination.

Visual perception of others actions is important for social interactions, and the ability to do so, even when one gets only brief glimpses of others behavior, may be crucial for survival. At present it is unknown how the human brain solves this problem. Imaging studies have promoted the idea that the multiple demand (MD) system, a domain general system of the human brain, operates in difficult cognitive and perceptual tasks, but not in tasks in which sensory information is reduced. Functional imaging, based on slow hemodynamic responses, may miss or standardize neural events with very diverse time courses. Here we exploited the temporal resolution of stereo-EEG to study directly cortical activity when human subjects must judge the actions of others, but only get brief glimpses of others activity, because the videos were truncated. Multiple cortical regions increased their activity in the difficult action discrimination, relative to the easy task when the complete video was visible. The majority of these regions belonged to the MD system, being located in parietal or prefrontal cortex. The variety of time courses, lasting from a few 100ms to several seconds, allowed us to disentangle control from effector regions, the latter processing observed actions. This distinction was further supported by relationships with behavior. A key operation within the control clusters was the prediction of erroneous responses, which was initiated in the PPC soon after the end of the truncated video. The time courses further suggested that MD regions not only exert control, but also perform various evaluations of the effort, important for efficient and intelligent behavior. We observed also increases outside the MD system, in temporo-parietal cortex, which may provide contextual information about variables related to the observed action, such as the actor, the object or the scene. Furthermore, to cope with the brief sensory input, the MD system called upon warning regions reacting to the static picture of the actor presented just before the video. We conclude that discrimination of brief observed actions indeed involves the MD system, which is thus is more general than assumed so far. WE also show that the MD system is more complex than assumed, as it includes evaluation of control, and more flexible, as it interacts with other systems than simply the effector circuit of the task.

neuroscience↗

bioRxiv2019

Disentangling sound from syntax: electrophysiological analysis of linguistics expressions

Syntax is a species-specific component of human language combining a finite set of words in a potentially infinite number of sentences. Since words are by definition expressed by sound, factoring out syntactic information is normally impossible. Here, we circumvented this problem in a novel way by designing phrases with exactly the same acoustic content but different syntactic structures depending on the other words they occur with. By performing stereo- electroencephalographic (SEEG) recordings in epileptic patients we measured a different electrophysiological correlate of verb phrases vs. noun phrases by analyzing the high gamma band activity (150-300Hz frequency), in multiple cortical areas in both hemispheres, including language areas and their homologous in the non-dominant hemisphere. Our findings contribute to the ultimate goal of a complete neural decoding of linguistic structures from the brain.

neuroscience↗

bioRxiv2019

Electrophysiological correlates of syntactic structures

Syntax is traditionally defined as a specifically human way to pair sound with meaning: words are assembled in a recursive way generating a potentially infinite set of sentences1,2. There can be different phrasal structures depending on the types of words involved, for example, \"noun phrases\" (NP), combining an article and a noun, vs. \"verb phrases\" (VP), combining a verb and a complement. Although it is known that the combination of an increasing number of words in sequences correlates with an increasing electrophysiological activity3,4, the specific electrophysiological correlates of the syntactic operation generating NPs vs. VPs remain unknown. A major confounding factor is the fact that syntactic information is inevitably intertwined with the acoustic information contained in words even during inner speech5. Here, we addressed this issue in a novel way by designing a paradigm to factor out acoustic information and isolate the syntactic component. In particular, we construed phrases that have exactly the same acoustic content but that are interpreted as NPs or VPs depending on their syntactic context (homophonous phrases). By performing stereo-electro-encephalographic (SEEG) recordings in epileptic patients6 we show that VPs are associated with a higher activity in the high gamma band (150-300Hz frequency), an index of cortical activity associated with linguistic processing, with respect to NPs in multiple cortical areas in both hemispheres, including language areas and their homologous in the non-dominant hemisphere. Our findings pave the way to a deeper understanding of the electrophysiological mechanisms underlying syntax and contribute to the ultimate far reaching goal of a complete neural decoding of linguistic structures from the brain2.

neuroscience↗