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When we look at our body parts, we are immediately aware that they belong to us and we rarely doubt about the integrity, continuity, and sense of ownership of our body. Despite this certainty, immersive virtual reality (IVR) may lead to a strong feeling of embodiment over an artificial body part seen from a first-person perspective (1PP). Although such feeling of ownership (FO) has been described in different situations, it is not yet understood how this phenomenon is generated at neural level. To track the real-time brain dynamics associated with FO, we delivered transcranial magnetic stimuli over the hand region in the primary motor cortex (M1) and simultaneously recorded electroencephalography (EEG) in 19 healthy volunteers (11 male/8 female) watching IVR renderings of anatomically plausible (full-limb) versus implausible (hand disconnected from the forearm) virtual limbs. Our data show that embodying a virtual hand is temporally associated with a rapid drop of cortical activity of the onlookers' hand region in the M1 contralateral to the observed hand. Spatiotemporal analysis shows that embodying the avatar's hand is also associated with fast changes of activity within an interconnected fronto-parietal circuit ipsilateral to the brain stimulation. Specifically, an immediate reduction of connectivity with the premotor area is paralleled by an enhancement in the connectivity with the posterior parietal cortex (PPC) which is related to the strength of ownership illusion ratings and thus likely reflects conscious feelings of embodiment. Our results suggest that changes of bodily representations are underpinned by a dynamic cross talk within a highly-plastic, fronto-parietal network.SIGNIFICANCE STATEMENTObserving an avatar's body part from a first-person perspective (1PP) induces an illusory embodiment over it. What remains unknown are the cortical dynamics underpinning the embodiment of artificial agents. To shed light on the physiological mechanisms of embodiment we used a novel approach that combines noninvasive stimulation of the cortical motor-hand area and whole-scalp electroencephalographic (EEG) recordings in people observing an embodied artificial limb. We found that just before the illusion started, there is a decrease of activity of the motor-hand area accompanied by an increase of connectivity with the parietal region ipsilateral to the stimulation that reflects the ratings of the embodiment illusion. Our results suggest that changes of bodily representations are underpinned by a dynamic cross talk within a fronto-parietal circuit.

EEG studies show that observing errors in one's own or others' actions triggers specific electro-cortical signatures in the onlooker's brain, but whether the brain error-monitoring system operates according to graded or discrete rules is still largely unknown. To explore this issue, we combined immersive virtual reality with EEG recording in participants who observed an avatar reaching-to-grasp a glass from a first-person perspective. The avatar could perform correct or erroneous actions. Erroneous grasps were defined as small or large depending on the magnitude of the trajectory deviation from the to-be-grasped glass. Results show that electro-cortical indices of error detection (indexed by ERN and mid-frontal theta oscillations), but not those of error awareness (indexed by error-Positivity), were gradually modulated by the magnitude of the observed errors. Moreover, the phase connectivity analysis revealed that enhancement of mid-frontal theta phase synchronization paralleled the magnitude of the observed error. Thus, theta oscillations represent an electro-cortical index of the degree of control exerted by mid-frontal regions whose activation depends on how much an observed action outcome results maladaptive for the onlooker. Our study provides novel neurophysiological evidence that the error monitoring system maps observed errors of different magnitude according to fine-grain, graded rather than all-or-none rules.

To explore the link between Sense of Embodiment (SoE) over a virtual hand and physiological regulation of skin temperature, 24 healthy participants were immersed in virtual reality through a Head Mounted Display and had their real limb temperature recorded by means of a high-sensitivity infrared camera. Participants observed a virtual right upper limb (appearing either normally, or with the hand detached from the forearm) or limb-shaped non-corporeal control objects (continuous or discontinuous wooden blocks) from a first-person perspective. Subjective ratings of SoE were collected in each observation condition, as well as temperatures of the right and left hand, wrist and forearm. The observation of these complex, body and body-related virtual scenes resulted in increased real hand temperature when compared to a baseline condition in which a 3d virtual ball was presented. Crucially, observation of non-natural appearances of the virtual limb (discontinuous limb) and limb-shaped non-corporeal objects elicited high increase in real hand temperature and low SoE. In contrast, observation of the full virtual limb caused high SoE and low temperature changes in the real hand with respect to the other conditions. Interestingly, the temperature difference across the different conditions occurred according to a topographic rule that included both hands. Our study sheds new light on the role of an external hand's visual appearance and suggests a tight link between higher-order bodily self-representations and topographic regulation of skin temperature.

The digit span is one of the most widely used memory tests in clinical and experimental neuropsychology for reliably measuring short-term memory capacity. In the forward version, sequences of digits of increasing length have to be reproduced in the order in which they are presented, whereas in the backward version items must be reproduced in the reversed order. Here, we assessed whether transcranial alternating current stimulation (tACS) increases the memory span for digits of young and midlife adults. Imperceptibly weak electrical currents in the alpha (10 Hz), beta (20 Hz), theta (5 Hz), and gamma (40 Hz) range, as well as a sham stimulation, were delivered over the left posterior parietal cortex, a cortical region thought to sustain maintenance processes in short-term memory through oscillatory brain activity in the beta range. We showed a frequency-specific effect of beta-tACS that robustly increased the forward memory span of young, but not middle-aged, healthy individuals. The effect correlated with age: the younger the subjects, the greater the benefit arising from parietal beta stimulation. Our results provide evidence of a short-term memory capacity improvement in young adults by online frequency-specific tACS application.

Cognitive control during conflict monitoring, error processing, and post-error adjustment appear to be associated with the occurrence of midfrontal theta (MFϴ). While this association is supported by correlational EEG studies, much less is known about the possible causal link between MFϴ and error and conflict processing. In the present study, we aimed to explore the role of band-specific effects in modulating the error system during a conflict resolution. In turn, we delivered transcranial alternating current stimulation (tACS) at different frequency bands (delta δ, theta θ, alpha α, beta β, gamma γ) and sham stimulation over the medial frontal cortex (MFC) in 36 healthy participants performing a modified version of the Flanker task. Task performance and reports about the sensations (e.g. visual flickering, cutaneous burning) induced by the different frequency bands, were also recorded. We found that online θ-tACS increased the response speed to congruent stimuli after error execution with respect to sham stimulation. Importantly, the accuracy following the errors did not decrease because of speed-accuracy trade off. Moreover, tACS evoked visual and somatosensory sensations were significantly stronger at α-tACS and β-tACS compared to other frequencies. Our findings suggest that theta activity plays a causative role in modulating behavioural adjustments during perceptual choices in a stimulus-response conflict task.

The mental representation of one's body typically implies the continuity of its parts. Here, we used immersive virtual reality to explore whether mere observation of visual discontinuity between the hand and limb of an avatar could influence a person's sense of ownership of the virtual body (feeling of ownership, FO) and being the agent of its actions (vicarious agency, VA). In experiment 1, we tested whether placing different amounts of visual discontinuity between a virtual hand and limb differently modulate the perceived FO and VA. Participants passively observed from a first-person perspective four different versions of a virtual limb: (1) a full limb; a hand detached from the proximal part of the limb because of deletion of (2) the wrist; (3) the wrist and forearm; (4) and the wrist, forearm and elbow. After observing the static or moving virtual limb, participants reported their feeling of ownership (FO) and vicarious agency (VA) over the hand. We found that even a small visual discontinuity between the virtual hand and arm significantly decreased participants' FO over the hand during observation of the static limb. Moreover, in the same condition, we found that passive observation of the avatar's actions induced a decrease in both FO and VA. We replicated the same results in a second study (experiment 2) where we investigated the modulation of FO and VA by comparing the visual body discontinuity with a condition in which the virtual limb was partially occluded. Our data show that mere observation of limb discontinuity can change a person's ownership and agency over a virtual body observed from a first-person perspective, even in the absence of any multisensory stimulation of the real body. These results shed new light on the role of body visual continuity in modulating self-awareness and agency in immersive virtual reality.

Categorical clustering in the visual system is thought to have evolved as a function of intrinsic (intra-areal) and extrinsic (interareal) connectivity and experience. In the visual system, the extrastriate body area (EBA), an occipito-temporal region, responds to full body and body part images under the organizational principle of their functional/semantic meaning. Although frequency-specific modulations of neural activity associated with perceptive and cognitive functions are increasingly attracting the interest of neurophysiologists and cognitive neuroscientists, perceiving single body parts with different functional meaning and full body images induces time-frequency modulations over occipito-temporal electrodes are yet to be described. Here, we studied this issue by measuring EEG in participants who passively observed fingers, hands, arms and faceless full body images with four control plant stimuli, each bearing hierarchical analogy with the body stimuli. We confirmed that occipito-temporal electrodes (compatible with the location of EBA) show a larger event-related potential (ERP, N190) for body-related images. Furthermore, we identified a body part-specific (i.e. selective for hands and arms) theta event-related synchronization increase under the same electrodes. This frequency modulation associated with the perception of body effectors over occipito-temporal cortices is in line with recent findings of categorical organization of neural responses to human effectors in the visual system.

During encoding, the neural activity immediately before or during an event can predict whether that event will be later remembered. The contribution of brain activity immediately after an event to memory formation is however less known. Here, we used repetitive Transcranial Magnetic Stimulation (rTMS) to investigate the temporal dynamics of episodic memory encoding with a focus on post-stimulus time intervals. At encoding, rTMS was applied during the online processing of the word, at its offset, or 100, 200, 300 or 400 ms thereafter. rTMS was delivered to the left ventrolateral (VLPFC) or dorsolateral prefrontal cortex (DLPFC). VLPFC rTMS during the first few hundreds of milliseconds after word offset disrupted subsequent recognition accuracy. We did not observe effects of DLPFC rTMS at any time point. These results suggest that encoding-related VLPFC engagement starts at a relatively late processing stage, and may reflect brain processes related to the offset of the stimulus.

Spatial attention is a key factor in the exploration and processing of the surrounding environment, and plays a role in linking magnitudes such as space, time, and numbers. The present work evaluates whether shifting the coordinates of spatial attention through rotational head movements may affect the ability to estimate the duration of different time intervals. A computer-based implicit timing task was employed, in which participants were asked to concentrate and report verbally on colour changes of sequential stimuli displayed on a computer screen; subsequently, they were required to reproduce the temporal duration (ranging between 5 and 80 sec.) of the perceived stimuli using the computer keyboard. There was statistically significant overestimation of the 80-sec. intervals exclusively on the rightward rotation head posture, whereas head posture did not affect timing performances on shorter intervals. These findings support the hypothesis that the coordinates of spatial attention influence the ability to process time, consistent with the existence of common cortical metrics of space and time in healthy humans.

Deception is a pervasive phenomenon that greatly influences dyadic, groupal and societal interactions. Behavioural, physiological and neural signatures of this phenomenon have imporant implications for theoretical and applied research, but, because it is difficult for a laboratory to replicate the natural context in which deception occurs, contemporary research is still struggling to find such signatures. In this study, we tracked the facial temperature of participants who decided whether or not to deceive another person, in situations where their reputation was at risk or not. We used a high-sensitivity infrared device to track temperature changes to check for unique patterns of autonomic reactivity. Using a region-of-interest based approach we found that prior to any response there was a minimal increase in periorbital temperature (which indexes sympathetic activation, together with reduced cheek temperature) for the self-gain lies in the reputation-risk condition. Crucially, we found a rise in nose temperature (which indexes parasympathetic activation) for self-gain lies in the reputation-risk condition, not only during response preparation but also after the choice was made. This finding suggests that the entire deception process may be tracked by the nose region. Furthermore, this nasal temperature modulation was negatively correlated with machiavellian traits, indicating that sympathetic/parasympathetic regulation is less important for manipulative individuals who may care less about the consequences of lie-related moral violations. Our results highlight a unique pattern of autonomic reactivity for spontaneous deception in ecological contexts.

When we look at our hands we are immediately aware that they belong to us and we rarely doubt about the integrity, continuity and sense of ownership of our bodies. Here we explored whether the mere manipulation of the visual appearance of a virtual limb could influence the subjective feeling of ownership and the physiological responses (Skin Conductance Responses, SCRs) associated to a threatening stimulus approaching the virtual hand. Participants observed in first person perspective a virtual body having the right hand-forearm (i) connected by a normal wrist (Full-Limb) or a thin rigid wire connection (Wire) or (ii) disconnected because of a missing wrist (m-Wrist) or a missing wrist plus a plexiglass panel positioned between the hand and the forearm (Plexiglass). While the analysis of subjective ratings revealed that only the observation of natural full connected virtual limb elicited high levels of ownership, high amplitudes of SCRs were found also during observation of the non-natural, rigid wire connection condition. This result suggests that the conscious embodiment of an artificial limb requires a natural looking visual body appearance while implicit reactivity to threat may require physical body continuity, even non-naturally looking, that allows the implementation of protective reactions to threat.

Detecting others' action errors plays a critical role in social life. Studies indicate that executing action errors and observing other's errors activate a specific cerebral system specialized for performance monitoring and detecting mismatches between an internal model of the action and the executed/observed one. Such a system may be particularly important for highly skilled performance. By recording electro-encephalographic (EEG) activity in expert pianists, non-pianist musicians and musically naive individuals while they observed correct or incorrect mute piano sequences, we explored the link between sensorimotor expertise, the ability to detect another's erroneous action (indexed by positivity error, Pe) and action simulation (indexed by mu frequency suppression). Superior error detection in pianists was paralleled by a larger Pe, hinting at the selective activation of the parietal error-monitoring system in visuo-motor experts. Moreover, only in pianists did action observation induce left lateralized mu suppression in the 10-12 Hz band, reflecting somatotopic sensorimotor simulation. A mediation analysis showed that mu suppression and performance (indexed by d') were mediated by Pe amplitude, indicating that the higher the simulation, the higher the sensitivity to errors for large Pe amplitude. This study shows that specific electrocortical indices link motor simulation and detection of errors in the actions of others.

During social interactions people automatically apply stereotypes in order to rapidly categorize others. Racial differences are among the most powerful cues that drive these categorizations and modulate our emotional and cognitive reactivity to others. We investigated whether implicit racial bias may also shape hand kinematics during the execution of realistic joint actions with virtual in- and out-group partners. Caucasian participants were required to perform synchronous imitative or complementary reach-to-grasp movements with avatars that had different skin color (white and black) but showed identical action kinematics. Results demonstrate that stronger visuo-motor interference (indexed here as hand kinematics differences between complementary and imitative actions) emerged: i) when participants were required to predict the partner's action goal in order to on-line adapt their own movements accordingly; ii) during interactions with the in-group partner, indicating the partner's racial membership modulates interactive behaviors. Importantly, the in-group/out-group effect positively correlated with the implicit racial bias of each participant. Thus visuo-motor interference during joint action, likely reflecting predictive embodied simulation of the partner's movements, is affected by cultural inter-individual differences.

Although universal, lying is generally considered immoral behavior. Most neuroscience studies on lying sanction or instruct deceptive behaviors and thus might fail to acknowledge the significance of lie-related moral conflicts. By combining electroencephalogram (EEG) recordings with a novel paradigm in which participants decided freely whether to deceive another person, we have generated indices of the cognitive (reaction times and stimulus-locked event-related components) and moral (readiness potential and its correlations with deception-related personality traits) cost of spontaneous deception. Our data fail to support the consensus that deception is cognitively more demanding than truth telling, suggesting that spontaneous deception, as opposed to lying out of requirement, might not mandate additional cognitive workload. Interestingly, lying was associated with decreased motor readiness, an event-related potential (ERP) component that is linked to motor preparation of self-determined actions and modulated when we face moral dilemmas. Notably, this reduction was less extensive in manipulative participants and greater in those who cared highly about their impression management. Our study expands on previous findings on deception by associating a cortical marker of reduced preparation to act with individual differences in moral cognition.

Studies indicate that physical and social pain may share some mechanisms and neural correlates. Nothing is known, however, on whether the neural activity in the nociceptive system, as indexed by laser-evoked potentials (LEPs), is modified when suffering the consequences of a conspecific violating social norms. To explore this issue, we created an interaction scenario where participants could gain money by performing a time-estimation task. On each win-trial, another player connected online could arbitrarily decide to keep the participant's pay-off for him- or herself. Thus, participants knew that monetary loss could occur because of their own failure in performing the task or because of the inequitable behavior of another individual. Moreover, participants were asked to play for themselves or on behalf of a third party. In reality, the win/loss events were entirely decided by an ad hoc programmed computer. At the end of the interaction, participants reported if they believed the game-playing interaction was real. Results showed that the loss due to the opponent's inequitable behavior brought about a reduction both in pain intensity self-reports and in the amplitude of LEPs' components (i.e., N2, N2/P2, P2a, P2b). Importantly, both the behavioral and neurophysiological effects were found in the participants who believed their deserved payoff was stolen by their opponent. Furthermore, reduction of vertex components was present only when the inequitable behavior was directed toward the self. These results suggest that, far from being a private experience, pain perception might be modulated by the social saliency of interpersonal interactions.

Prediction of "when" a partner will act and "what" he is going to do is crucial in joint-action contexts. However, studies on face-to-face interactions in which two people have to mutually adjust their movements in time and space are lacking. Moreover, while studies on passive observation have shown that somato-motor simulative processes are disrupted when the observed actor is perceived as an out-group or unfair individual, the impact of interpersonal perception on joint-actions has never been directly addressed. Here we explored this issue by comparing the ability of pairs of participants who did or did not undergo an interpersonal perception manipulation procedure to synchronise their reach-to-grasp movements during: i) a guided interaction, requiring pure temporal reciprocal coordination, and ii) a free interaction, requiring both time and space adjustments. Behavioural results demonstrate that while in neutral situations free and guided interactions are equally challenging for participants, a negative interpersonal relationship improves performance in guided interactions at the expense of the free interactive ones. This was paralleled at the kinematic level by the absence of movement corrections and by low movement variability in these participants, indicating that partners cooperating within a negative interpersonal bond executed the cooperative task on their own, without reciprocally adapting to the partner's motor behaviour. Crucially, participants' performance in the free interaction improved in the manipulated group during the second experimental session while partners became interdependent as suggested by higher movement variability and by the appearance of interference between the self-executed actions and those observed in the partner. Our study expands current knowledge about on-line motor interactions by showing that visuo-motor interference effects, mutual motor adjustments and motor-learning mechanisms are influenced by social perception. © 2012 Sacheli et al

Does opportunity make the thief or are people dispositionally prone to deceive? The interaction between personality and the circumstances surrounding deception is crucial to understand what promotes dishonesty in our society. Due to its inherent spontaneity and sociality, deceptive behaviour may be hardly reproducible in experimental settings. We developed a novel paradigm in the form of an interactive game where participants can choose whether to lie to another person in situations of loss vs. gain, and of no-reputation-risk vs. reputation-risk linked to the disclosure of their deceptive behaviour to others. Thus, our ecological paradigm allowed subjects to spontaneously decide when to lie and face the challenge of deceiving others. In the case of loss, participants lied to reverse the outcome in their favour. Deception was lower in the reputation-risk condition where personality traits concerning social interactions also played an important role. The results suggest that deception is definitely promoted by unfavourable events, and that maintaining one's own reputation encourages honesty, particularly in socially inclined individuals.

To investigate whether the mechanisms underlying endogenous tactile spatial attention differ under pure tactile compared to mixed modality conditions event-related brain potentials (ERPs) were recorded to bilateral tactile and visual cues and tactile imperative stimuli. In the cue-stimulus interval the anterior directing attention negativity (ADAN) was present contralateral to the side of the attentional shift. Importantly, under pure tactile conditions this component persisted until imperative stimulus onset, while it diminished under intermodal conditions. Furthermore, post-tactile stimulus onset attentional modulations were present for the P100 component and later latencies under intermodal conditions. In contrast, under pure tactile conditions attentional modulations only emerged for the N140 component and later latencies. It is suggested that mechanisms underlying attentional orienting and selection are not entirely supramodal but depend in part on the modalities involved.

To investigate the basis of crossmodal visual distractor congruency effects, we recorded event-related brain potentials (ERP) while participants performed a tactile location-discrimination task. Participants made speeded tactile location-discrimination responses to tactile targets presented to the index fingers or thumbs while ignoring simultaneously presented task-irrelevant visual distractor stimuli at either the same (congruent) or a different (incongruent) location. Behavioural results were in line with previous studies, showing slowed response times and increased error rates on incongruent compared with congruent visual distractor trials. To clarify the effect of visual distractors on tactile processing, concurrently recorded ERPs were analyzed for poststimulus, preresponse, and postresponse modulations. An enhanced negativity was found in the time range of the N2 component on incongruent compared with congruent visual distractor trials prior to correct responses. In addition, postresponse ERPs showed the presence of error-related negativity components on incorrect-response trials and enhanced negativity for congruent-incorrect compared with incongruent-incorrect trials. This pattern of ERP results has previously been related to response conflict (Yeung, Botvinick, & Cohen, 2004). Importantly, no modulation of early somatosensory ERPs was present prior to the N2 time range, which may have suggested the contribution of other perceptual or postperceptual processes to crossmodal congruency effects. Taken together, our results suggest that crossmodal visual distractor effects are largely due to response conflict.

In this study, a combined repetitive transcranial magnetic stimulation/electroencephalography (rTMS/EEG) method was used to explore the acute changes of cortical oscillatory activity induced by intermittent short trains of high-frequency (5-Hz) rTMS delivered over the left primary motor cortex (M1). We evaluated the electrophysiological reaction to magnetic stimulation during and 2-4 s after 20 trains of 20-pulses rTMS, using event-related power (ERPow) that reflects the regional oscillatory activity of neural assemblies, and event-related coherence (ERCoh) that reflects the interregional functional connectivity of oscillatory neural activity. These event-related transformations were for the upper alpha (10-12 Hz) and beta (18-22 Hz) frequency ranges, respectively. For the alpha band, threshold rTMS and subthreshold rTMS induced an ERPow increase during the trains of stimulation mainly in frontal and central regions ipsilateral to stimulation. For the beta band, a similar synchronization of cortical oscillations for both rTMS intensities was seen. Moreover, subthreshold rTMS affected alpha-band activity more than threshold rTMS, inducing a specific ERCoh decrease over the posterior regions during the trains of stimulation. For beta band, the decrease in functional coupling was observed mainly during threshold rTMS. These findings provide a better understanding of the cortical effects of high-frequency rTMS, whereby the induction of oscillations reflects the capacity of electromagnetic pulses to alter regional and interregional synaptic transmissions of neural populations. Hum Brain Mapp, 2008. (c) 2007 Wiley-Liss, Inc.

The aim of this study was to investigate the neural correlates of the functional distinction underlying attentional mechanisms of endogenous-sustained and exogenous-transient spatial selection. We recorded event related potentials (ERPs) and used functional magnetic resonance imaging (fMRI) in separate experiments while subjects performed a simple reaction time (RT) to the same visual stimulus displayed to one of several field locations. Endogenous-sustained or exogenous-transient focusing of attention onto target location were obtained by presenting the stimulus in blocks of same-point vs. randomised-point trials, respectively. Same-point stimuli yielded overall faster RT than randomised stimuli, indicating a facilitating effect of endogenous-sustained spatial attention on the perceptual processing of the impending stimulus. Moreover, same-point vs. randomised presentations revealed significant increases in the fMRI signal in the bilateral lingual and fusiform gyri as well as in the right calcarine sulcus, in conjunction with a larger amplitude of the posterior P1 component of ERPs, but no modulation of the amplitude of the N1 component. Rather, a larger amplitude of N1 was found in the reverse contrast, randomised minus same-point trials, which revealed increases in the fMRI signal along the posterior left superior frontal sulcus and bilaterally in the superior precuneus. These findings indicate that N1 indexes exogenous orienting of attention and is likely to represent the activity of frontal and parietal components of the attention network involved in eliciting attention changes. In contrast, the effects of those changes, resulting in a modulation of activation in visual occipital areas, are indexed by P1.

To gain insight into the neural basis of visual attention, we combined transcranial magnetic stimulation (TMS) and event-related potentials (ERPs) during a visual search task. Single-pulse TMS over right posterior parietal cortex (rPPC) delayed response times to targets during conjunction search, and this behavioral effect had a direct ERP correlate. The early phase of the N2pc component that reflects the focusing of attention onto target locations in a search display was eliminated over the right hemisphere when TMS was applied there but was present when TMS was delivered to a control site (vertex). This finding demonstrates that rPPC TMS interferes with attentional selectivity in remote visual areas.