Biology subjects

Barchiesi, G.

Publications and source records attributed to Barchiesi, G..

11 recordsLinked to original sources

bioRxiv2025

MEP-independent silent periods in hand muscles elicited by Transcranial Magnetic Stimulation of the ventral premotor cortex: a non-invasive tool to explore premotor negative motor areas

ObjectiveWe investigate the possibility to disrupt motor activity via premotor and parietal cortex stimulation, by inducing cortical silent periods (cSPs) in the voluntarily activated upper limb. MethodsWe analyzed data from 17 subjects with normal brain function, using navigated TMS (nTMS) on individual MR anatomies. We applied single-pulse biphasic stimulation at 120% of resting motor threshold (rMT) in blocks of 30 stimulations on each spot of a 10-16 point grid covering the inferior parietal and frontal lobes in the dominant hemisphere while participants performed voluntary submaximal contraction. Electromyography (EMG) was recorded bilaterally from intrinsic hand muscles. ResultsWe observed cSPs not preceded by a MEP in the contralateral hand in 16/17 participants. The maximum overlap, of individual areas where such MEP-independent cSPs could be evoked, corresponded to the ventral precentral gyrus (MNI coordinates: [x=-57, y=7, z=33]). In a subset of stimulus sites, MEP-independent cSPs were bilateral, with contralateral predominance. Canonical short-latency MEPs were observed in all patients, with maximum overlap over the primary motor cortex. We also observed rare contralateral long-latency (> 23 ms) MEP-like responses from peri-Rolandic TMS. ConclusionsMEP-independent cSPs are systematically elicitable in healthy participants They likely reflect interference with premotor representations of ongoing movements. They offer a novel possibility to investigate higher-order motor functions in the experimental and clinical neurosciences.

neuroscience↗

bioRxiv2025

Rational Expectations and Kinematic Information in Coordination Games

Successful coordination often requires integrating strategic reasoning with real-time observations of others actions, yet how humans resolve conflicts between these information sources remains unclear. This study aimed to fill this gap by examining how people coordinate in a strategic game when observing partial kinematic information from their partners actions. Participants played a HI-LO game with a virtual partner, choosing payoffs based on grasping movements toward invisible large and small targets. Hand movements were presented as schematic animations, with partners grasping targets linked to higher or lower payoffs across two configurations. Participants relied exclusively on kinematic cues from hand shape changes in maximum grip aperture to infer their partners choices. There were two main findings. While participants preferred higher payoffs consistent with rational game-theoretic expectations, reliable kinematic cues overrode these expectations. When early grip aperture changes indicated the partner was reaching for a large target associated with a lower payoff, participants abandoned their default preference for higher payoffs. They chose the lower option instead, achieving a high coordination success rate. These findings demonstrate that people prioritize kinematic cues about others choices over theoretical assumptions about rational behavior when coordinating. This suggests that movement-based inferences about others actions in natural social interactions may be weighted more heavily than strategic reasoning when the two sources of information conflict.

neuroscience↗

bioRxiv2025

ACTION ENHANCEMENT DRIVES THE EMBODIMENT OF A SUPERNUMERARY ROBOTIC DIGIT

Wearable robotic supernumerary limbs enhance motor capabilities by leveraging principles from both engineering and neuroscience. Despite extensive research, how supernumerary limbs become embodied and the relationship between embodiment and artificially enhanced action possibilities remain largely unexplored. This gap has implications for device design and clinical adoption, as embodiment likely promotes patients acceptance and daily use of their supernumerary limb. Using an adapted proprioceptive drift paradigm from rubber hand illusion research, we investigated the embodiment of a robotic Soft Sixth Finger (SSF). Participants performed grasp-to-lift actions versus mere lift actions without object interaction, wearing the SSF on two different configurations: the palm and back of the hand. The Palm condition involved achievable actions without the SSF, while the Dorsal condition enabled otherwise anatomically impossible actions, extending beyond the physiological motor repertoire. Hand proprioceptive drift was measured before and after each task. Results showed that the SSF impacted body representation only when dorsally mounted. Proprioceptive drift was significantly higher for grasp-to-lift actions in Dorsal versus Palm conditions and higher for grasp-to-lift versus mere lift in the Dorsal condition only. This proves that SSF embodiment relates to extending, rather than substituting, users action possibilities. Future research must integrate behavioral, cognitive, and neural measurements across healthy and patient populations. Our study provides an ideal model for clinical application, demonstrating how enabling otherwise impossible actions drives robotic supernumerary finger embodiment.

neuroscience↗

bioRxiv2025

EARLY TARGET PREDICTION IN ACTION OBSERVATION

Previous research has established that observers can predict action targets through hand preshaping. However, two critical questions remain unexplored: how predictions adapt to the available kinematic information and evolve throughout the movement timeline. We address these fundamental gaps by combining kinematic analysis with machine-learning approaches that differentiate between motor and visual cues. Using motion capture technology, we recorded reach-to-grasp actions toward large and small objects and had participants predict target size from hand kinematics at varying time points. Our analysis revealed that prediction performance not only evolved with increasing kinematic information but, crucially, differed significantly between target size choices. To provide insight into the underlying processes, we developed a comparative framework using two distinct machine learning approaches: Support Vector Machines (SVM) modeling kinematic information and CNN-RNN networks extracting visual patterns. The stronger alignment between human performance and SVM predictions offers empirical evidence that kinematic cues, rather than visual patterns, mostly guide target prediction. These findings advance our understanding of action prediction and have significant implications for social cognition and human-machine interaction. PUBLIC SIGNIFICANCE STATEMENTUnderstanding others intentions by observing their hand movements is crucial for social interaction, from passing objects to coordinating complex tasks. This study reveals that people use different cues to predict whether someone is reaching for a large versus a small object from the earliest stages of hand movement. By comparing human performance with Artificial Intelligence models, we found that people primarily rely on motor cues to make these predictions. These insights could improve rehabilitation techniques for individuals with social interaction difficulties and enhance the design of intuitive robotic assistants.

neuroscience↗

bioRxiv2025

How Acting Jointly Differs from Acting Side-by-Side: A Dual EEG Study

The distinction between acting jointly and acting side by side permeates our daily lives and is crucial for understanding the evolution and development of human sociality. While acting in parallel involves agents pursuing individual goals, acting jointly requires them to share a collective goal. Here, we used a dual electroencephalography (EEG) approach to explore the neural dynamics underlying joint and parallel action preparation. We recorded event-related potentials (ERPs) from 20 dyads while they had to transport an object in a video game, either jointly or in parallel, or individually. Both conditions were carefully matched for coordination demands and performance complexity, as confirmed by equal success rates. Our results revealed a distinctive pattern swap in ERPs during action preparation. In the early preparation phase, ERPs showed significantly higher amplitude during joint action than parallel action. This pattern reversed in the late preparation phase, with significantly reduced ERP amplitude in the joint compared to parallel action. Notably, the decrease in late ERPs correlated with higher reaction time (RT) variability in partners but not with participants own RT variability. The dynamic swap in neural activity suggests that different cognitive processes operate at distinct stages of action preparation. While initially sharing a collective goal may impose cognitive costs (reflected in higher early ERPs), this is offset by facilitated late action preparation, likely due to enhanced predictability of partners actions. Significance StatementOur study reveals distinct neural signatures differentiating joint from side-by-side actions. Through dual EEG recordings of twenty dyads performing complexity-matched tasks, we identified a distinctive "swap" in event-related potentials during action preparation. Joint actions initially showed higher early-phase amplitudes but significantly reduced late-phase amplitudes compared to parallel actions. Notably, this late-phase reduction correlated specifically with the variability of partners behavior. This suggests that sharing collective goals initially requires cognitive resources but facilitates action preparation through enhanced predictability of partners. These findings provide a neural framework for understanding the distinction between acting jointly and acting in parallel --a distinction that pervades our daily experiences and is crucial for understanding the development and evolution of human sociality.

neuroscience↗

bioRxiv2025

High-frequency sampling rate reduces TMS-pulse artifact duration but not decay artifact: implications for immediate TMS-EEG responses

In studies combining transcranial magnetic stimulation and electroencephalography (TMS-EEG), two artifacts appear instantly after the TMS pulse, i.e., the TMS-pulse Artifact and the Decay Artifact, and limit the possibility to measure immediate cortical excitability responses. High-frequency sampling rates in EEG recordings have shown promise in reducing artifact duration, allowing more rapid signal recovery, which is crucial for developing biomarkers for neuropsychiatric conditions. However, the features of early TMS-induced artifacts for sampling rates above 5000 Hz are still unclear. Here, we explored the duration of TMS artifacts in the first milliseconds after TMS to understand how they can be further reduced in future studies. We recorded from a phantom head model and from a simple electrical circuit with a sampling rate of 4800 Hz, 9600 Hz, and 19200 Hz and at three TMS intensities (40%, 70%, 100% of maximum stimulator output) in two commercial stimulators. Results showed an initial sharp TMS-pulse Artifact lasting less than 1 ms and decreasing in duration at higher sampling rates. However, the signal was back to baseline at about 2-3 ms due to the presence of a decay artifact that was evident even in optimal conditions of low impedance and mostly dependent on stimulation intensity. These results highlight the need to develop efficient ways to eliminate the decay artifact in order to measure immediate TMS responses.

neuroscience↗

bioRxiv2024

Stimulation parameters shape effective connectivity pathways: insights from microstate analysis on TMS-evoked potentials

Transcranial magnetic stimulation (TMS)-evoked potentials (TEPs) represent an innovative measure for examining brain connectivity and developing biomarkers of psychiatric conditions. Minimising TEP variability across studies and participants, which may stem from methodological choices, is therefore vital. By combining classic peak analysis and microstate investigation, we tested how TMS pulse waveform and current direction may affect effective connectivity when targeting the primary motor cortex (M1). We aim to disentangle whether changing these parameters affects the degree of activation of the same neural circuitry or may lead to changes in the pathways through which the induced activation spreads. Thirty-two healthy participants underwent a TMS-EEG experiment in which the pulse waveform (monophasic, biphasic) and current direction (posterior-anterior, anterior-posterior, latero-medial) were manipulated. We assessed the latency and amplitude of M1-TEP components and employed microstate analyses to test differences in topographies. Results revealed that TMS parameters strongly influenced M1-TEP components amplitude but had a weaker role over their latencies. Importantly, microstate analysis showed that the current direction in monophasic stimulations changed the pattern of evoked microstates at the early TEP latencies, as well as their duration and the overall amount of activated brain resources associated. This study shows that the current direction of monophasic pulses may modulate cortical sources contributing to TEP signals, activating neural populations and cortico-cortical paths more selectively. Biphasic stimulation reduces the variability associated with current direction and may be better suited when TMS targeting is blind to anatomical information.

neuroscience↗

bioRxiv2024

Immediate TMS-EEG responses reveal motor cortex excitability

BackgroundCombined transcranial magnetic stimulation and electroencephalography (TMS-EEG) is widely used to probe cortical excitability at the network level, but technical challenges have prevented its application to investigate local excitability of the stimulated area. A recent study revealed immediate TMS-evoked potentials (i-TEPs) after primary motor cortex (M1) stimulation, suggesting that it may represent a local response. Here, we aimed at testing if this activity is physiological in nature and what it represents. MethodsWe analyzed a TMS-EEG dataset from 28 healthy participants recorded at 9.6 kHz including two M1 stimulation conditions with opposite biphasic current directions. We localized the brain sources of i-TEPs, calculated the immediate TMS-related power (i-TRP) to distinguish between two oscillatory components that may contribute to i-TEPs, and investigated the relationship between i-TRP and motor-evoked potentials (MEPs). In an additional recording, we stimulated a control site evoking a muscular response to understand the contribution of the TMS-related muscle artifact. ResultsResults confirmed i-TEPs with similar characteristics as previously described. The i-TRP revealed strong activity in two ranges 600-800 Hz and 100-200 Hz; The former was positively associated with MEPs amplitude for both current direction conditions. Moreover, i-TEPs were localized in the precentral gyrus of the stimulated hemisphere and the muscular response generated by the control stimulation site differed from i-TEPs and i-TRP. DiscussionThese findings provide first evidence on the physiological nature of i-TEPs and i-TRP following M1 stimulation and that i-TRP represents a direct measure of excitability of the stimulated cortex.

neuroscience↗

bioRxiv2024

DOES EXPERIENCE MODULATE AUTOMATIC IMITATION? A NEW LOOK

Automatic imitation is a stimulus-response compatibility effect wherein observing an action automatically influences motor performance. However, the mechanism underlying this effect remains controversial. Associative Sequence Learning suggests that automatic imitation arises from contingent visual and motor activity associations. Prior studies have shown that exposure to counter-imitative training can alter these visuomotor associations, suggesting that automatic imitation can be modulated by experience. Here, we aim to bring new insight into how this modulation occurs by exploring the time course of automatic imitation before and after counter-imitative training. If automatic imitation is merely a result of contingent associations, as previously suggested, the effect should consistently be modulated following such training. However, if this is not the case, automatic imitation is not, or not only, a matter of contingent association, at least not as currently understood.

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bioRxiv2022

Reliability of M1-P15 as a cortical marker for transcallosal inhibition: a preregistered TMS-EEG study

BackgroundIn a recently published study combining transcranial magnetic stimulation and electroencephalography (TMS-EEG), we provided first evidence of M1-P15, an early component of TMS-evoked potentials, as a measure of transcallosal inhibition between motor cortices. However, considering the technical challenges of TMS-EEG recordings, further evidence is needed before M1-P15 can be considered a reliable index. ObjectiveHere, we aimed at validating M1-P15 as a cortical index of transcallosal inhibition, by replicating previous findings on its relationship with the ipsilateral silent period (iSP) and with performance in bimanual coordination. Moreover, we aimed at inducing a task-dependent modulation of transcallosal inhibition. MethodsA new sample of 32 healthy right-handed participants underwent behavioral motor tasks and TMS-EEG recording, in which left and right M1 were stimulated during bimanual tasks and during an iSP paradigm. Hypotheses and methods were preregistered before data collection. ResultsWe successfully replicated our previous findings on the positive relationship between M1-P15 amplitude and the iSP normalized area. However, we did not confirm the relationship between M1-P15 latency and bimanual coordination. Finally, we show a task-dependent modulation of M1-P15 amplitude, which was affected by the characteristics of the bimanual task the participants were performing, but not by the contralateral hand activity during the iSP paradigm. ConclusionsThe present results corroborate our previous findings in validating the M1-P15 as a reliable cortical marker of transcallosal inhibition, and provide novel evidence of its task-dependent modulation. Importantly, we demonstrate the feasibility of a preregistration approach in the TMS-EEG field to increase methodological rigor and transparency.

neuroscience↗

bioRxiv2019

Head MagnetoMyography (hMMG): a novel approach to monitor face and whole-head muscular activity

Muscular activity recording is of high basic science and clinical relevance and is typically achieved using electromyography (EMG). While providing detailed information about the state of a specific muscle, this technique has limitations such as the need for a-priori assumptions about electrode placement and difficulty with recording muscular activity patterns from extended body areas at once. For head and face muscle activity, the present work aimed to overcome these restrictions by exploiting magnetoencephalography (MEG) as a whole-head myographic recorder (head magnetomyography, hMMG). This is in contrast to common MEG studies, which treat muscular activity as artifact in electromagnetic brain activity. In a first proof-of-concept step, participants imitated emotional facial expressions performed by a model. Exploiting source projection algorithms, we were able to reconstruct muscular activity, showing spatial activation patterns in accord with the hypothesized muscular contractions. Going one step further, participants passively observed affective pictures with negative, neutral, or positive valence. Applying multivariate pattern analysis to the reconstructed hMMG signal, we were able to decode above chance the valence category of the presented pictures. Underlining the potential of hMMG, a searchlight analysis revealed that generally neglected neck muscles exhibit information on stimulus valence. Results confirm the utility of hMMG as a whole-head electromyographic recorder to quantify muscular activation patterns including muscular regions that are typically not recorded with EMG. This key advantage beyond conventional EMG has substantial scientific and clinical potential.

neuroscience↗