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Understanding how self-representation is built, maintained and updated across the lifespan is a fundamental challenge for cognitive psychology and neuroscience. Studies demonstrate that the detection of body-related multisensory congruency builds bodily and facial self-representations that are crucial to developing self-recognition. Studies showing that the bodily self is more malleable than previously believed were mainly concerned with full-bodies and non-facial body parts. Crucially, however, intriguing recent evidence indicates that simple experimental manipulations could even affect self-face representation that has long been considered a stable construct impervious to change. In this review, we discuss how Interpersonal Multisensory Stimulation (IMS) paradigms can be used to temporarily induce Enfacement, i.e., the subjective illusion of looking at oneself in the mirror when in fact looking at another person's face. We show that Enfacement is a subtle but robust phenomenon occurring in a variety of experimental conditions and assessed by multiple explicit and implicit measures. We critically discuss recent findings on i) the role of sensory extero/proprio-ceptive (visual, tactile, and motor) and interoceptive (cardiac) signals in self-face plasticity, ii) the importance of multisensory integration mechanisms for the bodily self, and iii) the neural network related to IMS-driven changes in self-other face processing, within the predictive coding theoretical framework.

Self-face representation is fundamentally important for self-identity and self-consciousness. Given its role in preserving identity over time, self-face processing is considered as a robust and stable process. Yet, recent studies indicate that simple psychophysics manipulations may change how we process our own face. Specifically, experiencing tactile facial stimulation while seeing similar synchronous stimuli delivered to the face of another individual seen as in a mirror, induces ‘enfacement’ illusion, i.e. the subjective experience of ownership of the other’s face and a bias in attributing to the self, facial features of the other person. Here we recorded visual Event-Related Potentials elicited by the presentation of self, other and morphed faces during a self-other discrimination task performed immediately after participants received synchronous and control asynchronous Interpersonal Multisensory Stimulation (IMS). We found that self-face presentation after synchronous as compared to asynchronous stimulation significantly reduced the late positive potential (LPP; 450–750 ms), a reliable electrophysiological marker of self-identification processes. Additionally, enfacement cancelled out the differences in LPP amplitudes produced by self- and other-face during the control condition. These findings represent the first direct neurophysiological evidence that enfacement may affect self-face processing and pave the way to novel paradigms for exploring defective self-representation and self-other interactions.

The Self-Attention Network (SAN) model (Humphreys and Sui, 2015) is a recent neurocognitive model to account for self-biases in the allocation of attention. It emerges from psychological, neuropsychological, and neuroimaging evidence on three phenomena: own-name effects, own-face effects, and self-biases in associative matching. Specifically, it posits that our responses to self-related stimuli are differentially subserved by a network comprising three nodes: (i) a general-purpose top-down attentional control network which involves the dorsolateral prefrontal cortex and the intra-parietal sulcus; (ii) a self-representation hub located in the ventromedial prefrontal cortex (vmPFC), and (iii) a bottom-up orientating mechanism which depends on the posterior superior temporal sulcus (pSTS). Accordingly, attentional shifts upon hearing our own name or seeing our own face would rely on interactions among such nodes, mimicking perceptual-saliency effects, and determining emergent behavior. Though attractive, this proposal features two major caveats. First, the evidence for own-name effects is inconsistent and undermined by psycholinguistic confounds. Second, the node proposed to subserve self-specific information lacks neurofunctional specificity. Here we discuss both issues and advance relevant methodological recommendations. The model resorts to own-name studies allegedly showing biases for self-related information. However, confirmatory evidence has not been consistently replicated (Yang et al., 2013), especially when own names are compared to other familiar names (e.g., Harris et al., 2004; Kawahara and Yamada, 2004; Tacikowski et al., 2011). Moreover, when they do emerge, own-name effects may be related to non-self-specific psycholinguistic confounds, such as familiarity and frequency. Familiar and frequent words are processed faster (Guttentag and Carroll, 1994) and yield distinctive electrophysiological modulations (Kutas and Federmeier, 2011). Subjectively, own names are typically more frequent and familiar than other proper and common names. Thus, it is difficult to rule out the impact of such variables on the observed effects. Moreover, there is no neuroanatomical evidence for a dissociation between own names and other proper or familiar names. A review of patients with selective deficits in recalling people's names found no support for a specialized mechanism supporting proper-name—let alone own-name—processing (Hanley and Kay, 1998). Finally, neuroimaging and lesion studies indicate that proper-name processing mainly involves left temporal structures and, less notably, subcortical structures (Semenza, 2006). None of these regions is part of the neuroanatomical components of the SAN model, and there is no rationale for why one's own name should rely on a network separate from that specialized in processing its overarching category. At the very least, the model should specify the relationship between the regions proposed to support own-name biases and the broader networks subserving lexical processing, in general, and proper names, in particular. The SAN model further posits that self-specific information is subserved by a putative brain region. The model includes “a self-representation hub housed in the ventromedial prefrontal cortex (vmPFC)” (Humphreys and Sui, 2015: 15; emphasis ours). However, this association lacks neurofunctional specificity. The vmPFC is critically engaged by any affective response shaped by conceptual information about specific outcomes (Roy et al., 2012), and by bottom-up processing of external and internal salient stimuli (Cona et al., 2015). Crucially, the vmPFC is key to assess the familiarity of others' faces (Gilboa et al., 2009) and to discriminate them as a function of their relevance (Pegors et al., 2015). Finally, when one's own name is compared with stimuli of similar personal relevance (e.g., the name of a significant other), vmPFC activity is not differentially modulated by self-biased information. So, rather than self-attention in particular, vmPFC activations seem to index increased affective meaning, relevance, or familiarity of self-faces. In brief, the vmPFC does not seem specific enough to constitute a distinct node subserving sui generis self-attention. A second caveat concerning the role of the vmPFC has been noted by Vallesi (2015). As this author argues, the model assumes strong and mostly unidirectional excitatory connections from the vmPFC to the pSTS. However, this claim is incompatible with lesion data showing that self-bias effects decrease after damage to the former region, but increase following damage to the latter (Sui et al., 2015a). Accordingly, Vallesi (2015) posits that vmPFC activity may be modulated via inhibitory feedback connections from the pSTS, a specification that is not captured by the putative SAN model. These caveats may be circumvented via methodological innovations. The confounds surrounding own-name research may be avoided through “new nickname” studies. Participants could be given ad hoc nicknames and be referred to by them systematically throughout an experimental session. All names would have the same frequency and familiarity at baseline (namely, zero), and they could be matched for other relevant psycholinguistic variables, such as length or phonological complexity. If an advantage for own nicknames is thus observed, claims for a self-attention bias could be more validly entertained. A conceptually similar paradigm, designed by the very proponents of the SAN model (Sui et al., 2012, 2015b), illustrates the potential usefulness of “new nickname” studies. For example, upon establishing arbitrary associations between geometric shapes and themselves or other people, participants then show reliable self-prioritization effects, independent of psycholinguistic confounds (Sui et al., 2012). This evidence supports the possible benefits of “new-nickname” studies: while these would involve a similar design, they would decrease perceptual-matching demands and more directly address biases in the specific domain of proper-name processing. Regarding neuroanatomical concerns, functional and structural connectivity analyses would help clarify whether there is a relationship among SAN hubs and regions for selective processing of own names/faces. Moreover, the (relative) specificity for self-information in the vmPFC could be tested by comparing stimuli with similar relevance and familiarity but with different degrees of self-related information. Finally, additional neuropsychological as well as effective and functional connectivity studies could help elucidate the role of excitatory and inhibitory connections between the vmPFC and the pSTS, showing whether the latter structure modulates self-information processing in the former (Vallesi, 2015). Until these limitations are addressed, the SAN model will remain psycholinguistically and neuroanatomically underspecified.

a b s t r a c t Humans perceive continuous speech through interruptions or brief noise bursts cancelling entire phonemes. This robust phenomenon has been classically associated with mechanisms of perceptual restoration. In parallel, recent experimental evidence suggests that the motor system may actively par- ticipate in speech perception, even contributing to phoneme discrimination. In the present study we intended to verify if the motor system has a specific role in speech perceptual restoration as well. To this aim we recorded tongue corticospinal excitability during phoneme expectation induced by contextual information. Results showed that phoneme expectation determines an involvement of the individual's motor system specifically implicated in the production of the attended phoneme, exactly as it happens during actual listening of that phoneme, suggesting the presence of a speech imagery-like process. Very interestingly, this motoric phoneme expectation is also modulated by subtle coarticulation cues of which the listener is not consciously aware. Present data indicate that the rehearsal of a specific phoneme requires the contribution of the motor system exactly as it happens during the rehearsal of actions exe- cuted by the limbs, and that this process is abolished when an incongruent phonemic cue is presented, as similarly occurs during observation of anomalous hand actions. We propose that altogether these effects indicate that during speech listening an attentional-like mechanism driven by the motor system, based on a feed-forward anticipatory mechanism constantly verifying incoming information, is working allowing perceptual restoration. © 2011 Elsevier Ltd. All rights reserved.

Self-face recognition is crucial for sense of identity and self-awareness. Finding self-face recognition disorders mainly in neurological and psychiatric diseases suggests that modifying sense of identity in a simple, rapid way remains a "holy grail" for cognitive neuroscience. By touching the face of subjects who were viewing simultaneous touches on a partner's face, we induced a novel illusion of personal identity that we call "enfacement": The partner's facial features became incorporated into the representation of the participant's own face. Subjects reported that morphed images of themselves and their partner contained more self than other only after synchronous, but not asynchronous, stroking. Therefore, we modified self-face recognition by means of a simple psychophysical manipulation. While accommodating gradual change in one's own face is an important form of representational plasticity that may help maintaining identity over time, the surprisingly rapid changes induced by our procedure suggest that sense of facial identity may be more malleable than previously believed. "Enfacement" correlated positively with the participant's empathic traits and with the physical attractiveness the participants attributed to their partners. Thus, personality variables modulate enfacement, which may represent a marker of the tendency to be social and may be absent in subjects with defective empathy.

Empathy may allow interindividual sharing not only of emotions (e.g., joy, sadness, disgust) but also of sensations (e.g., touch, itching, pain). Although empathy for pain may rely upon both sensory and affective components of the pain experience, neuroimaging studies indicate that only the affective component of the pain matrix is involved in empathy for pain. By using transcranial magnetic stimulation (TMS), we highlighted the sensorimotor side of empathy for pain by showing a clear motor inhibition during the mere observation of needles penetrating body parts of a human model. Here, we explored stimulus-specific and instruction-specific influences on this inhibition by manipulating task instructions (request to adopt first- or third-person perspective vs. passive observation) and painfulness of the experimental stimuli (presentation of videos of needles deeply penetrating or simply pinpricking a hand). We found a significant reduction in amplitudes of motor-evoked potentials (MEPs) specific to the muscle the subjects observed being penetrated that correlated with the intensity of the pain attributed to the model. Crucially, this motor inhibition was present during observation of penetrating but not of pinpricking needles. Moreover, no MEPs modulation contingent upon different task instructions was found. Results suggest that the motor inhibition elicited by the observation of ‘flesh and bone’ pain stimuli is more stimulus-driven than instruction-driven.

One's own face and gaze are never seen directly but only in a mirror. Yet, these stimuli capture attention more powerfully than others' face and gaze, suggesting the self is special for brain and behavior. Synchronous touches felt on one's own and seen on the face of others induce the sensation of including others in one's own face (enfacement). We demonstrate that enfacement may also reduce the overwhelming distracting power of self-gaze. This effect, hereafter called ‘engazement', depends on the perceived physical attractiveness and inner beauty of the pair partner. Thus, we highlight for the first time the close link between enfacement and engazement by showing that changes of the self-face representation induced by facial visuo-tactile stimulation extend to gaze following, a separate process likely underpinned by different neural substrates. Moreover, although gaze following is a largely automatic, engazement is penetrable to the influence of social variables, such as positive interpersonal perception.

The illusory subjective experience of looking at one's own face while in fact looking at another person's face can surprisingly be induced by simple synchronized visuotactile stimulation of the two faces. A recent study (Apps MA, Tajadura-Jiménez A, Sereno M, Blanke O, Tsakiris M. Cereb Cortex. First published August 20, 2013; doi:10.1093/cercor/bht199) investigated for the first time the role of visual unimodal and temporoparietal multimodal brain areas in the enfacement illusion and suggested a model in which multisensory mechanisms are crucial to construct and update self-face representation.

While several behavioral and neuroscience studies have explored visual, auditory, and cross-modal illusions, information about the phenomenology and neural correlates of somatosensory illusions is meager. By combining psychophysics and somatosensory evoked potentials, we explored in healthy humans the neural correlates of 2 compelling tactuo-proprioceptive illusions, namely Aristotle (1 object touching the contact area between 2 crossed fingers is perceived as 2 lateral objects) and Reverse illusions (2 lateral objects are perceived as 1 between crossed-fingers object). These illusions likely occur because of the tactuo-proprioceptive conflict induced by fingers being crossed in a non-natural posture. We found that different regions in the somatosensory stream exhibit different proneness to the illusions. Early electroencephalographic somatosensory activity (at 20 ms) originating in the primary somatosensory cortex (S1) reflects the phenomenal rather than the physical properties of the stimuli. Notably, later activity (around 200 ms) originating in the posterior parietal cortex is higher when subjects resist the illusions. Thus, while S1 activity is related to illusory perception, PPC acts as a conflict resolver that recodes tactile events from somatotopic to spatiotopic frames of reference and ultimately enables veridical perception.

Listening to speech recruits a network of fronto-temporo-parietal cortical areas. Classical models consider anterior, motor, sites involved in speech production whereas posterior sites involved in comprehension. This functional segregation is more and more challenged by action-perception theories suggesting that brain circuits for speech articulation and speech perception are functionally interdependent. Recent studies report that speech listening elicits motor activities analogous to production. However, the motor system could be crucially recruited only under certain conditions that make speech discrimination hard. Here, by using event-related double-pulse transcranial magnetic stimulation (TMS) on lips and tongue motor areas, we show data suggesting that the motor system may play a role in noisy, but crucially not in noise-free environments, for the discrimination of speech signals.

Psychological and neurophysiological experiments require the accurate control of timing and synchrony for Input/Output signals. For instance, a typical Event-Related Potential (ERP) study requires an extremely accurate synchronization of stimulus delivery with recordings. This is typically done via computer software such as E-Prime, and fast communications are typically assured by the Parallel Port (PP). However, the PP is an old and disappearing technology that, for example, is no longer available on portable computers. Here we propose a convenient USB device enabling parallel I/O capabilities. We tested this device against the PP on both a desktop and a laptop machine in different stress tests. Our data demonstrate the accuracy of our system, which suggests that it may be a good substitute for the PP with E-Prime.

Speech production can be broadly separated into two distinct components: Phonation and Articulation. These two aspects require the efficient control of several phono-articulatory effectors. Speech is indeed generated by the vibration of the vocal-folds in the larynx (F0) followed by ''filtering" by articulators, to select certain resonant frequencies out of that wave (F1, F2, F3, etc.). Recently it has been demonstrated that the motor representation of articulators (lips and tongue) participates in the discrimination of articulatory sounds (lips- and tongue-related speech sounds). Here we investigate whether the results obtained on articulatory sounds discrimination could be extended to phonation by applying a dual-pulse TMS protocol while subjects had to discriminate F0-shifted vocal utterances [a]. Stimulation over the larynx motor representation, compared to the control site (tongue/lips motor cortex), induced a reduction in RT for stimuli including a subtle pitch shift. We demonstrate that vocal pitch discrimination, in analogy with the articulatory component, requires the contribution of the motor system and that this effect is somatotopically organized.

The processes and neural bases used for motor imagery are also used for the actual execution of correspondent movements. Humans, however, can imagine movements they cannot perform. Here we explored whether plausibility of movements is mapped on the corticospinal motor system and whether the process is influenced by visuomotor vs. kinesthetic-motor first person imagery strategy. Healthy subjects imagined performing possible or biomechanically impossible right index finger movements during single pulse TMS of the left motor cortex. We found an increase of corticospinal excitability during motor imagery which was higher for impossible than possible movements and specific for the muscle involved in the actual execution of the imagined movement. We expand our previous action observation studies, suggesting that the plausibility of a movement is computed in regions upstream the primary motor cortex, and that motor imagery is a higher-order process not fully constrained by the rules that govern motor execution.

The study of inter-individual differences at behavioural and neural levels represents a new avenue for neuroscience. The response to socio-emotional stimuli varies greatly across individuals. For example, identification with the feelings of a movie character may be total for some people or virtually absent for others. Inter-individual differences may reflect both the on-line effect (state) of the observed stimuli and more stable personal characteristics (trait). Here we show that somatomotor mirror responses when viewing others' pain are modulated by both state- and trait-differences in empathy. We recorded motor-evoked potentials (MEPs) induced by Transcranial Magnetic Stimulation (TMS) in healthy individuals observing needles penetrating a model's hand. We found a reduction of corticospinal excitability that was specific for the muscle that subjects observed being penetrated. This inhibition correlated with sensory qualities of the pain ascribed to the model. Moreover, it was greater in subjects with high trait-cognitive empathy and lower in subjects with high trait-personal distress and in those with high aversion for the observed movies. Results indicate that somatomotor responses to others' pain are influenced by specific onlookers' personality traits and self-oriented emotional reactions. Our findings suggest that multiple distinct mechanisms shape mirror mapping of others' pain.

Although feeling pain and touch has long been considered inherently private, recent neuroimaging and neurophysiological studies hint at the social implications of this experience. Here we used somatosensory-evoked potentials (SEPs) to investigate whether mere observation of painful and tactile stimuli delivered to a model would modulate neural activity in the somatic system of an onlooker. Viewing video clips showing pain and tactile stimuli delivered to others, respectively, increased and decreased the amplitude of the P45 SEP component that reflects the activity of the primary somatosensory cortex (S1). These modulations correlated with the intensity but not with the unpleasantness of the pain and touch ascribed to the model or the aversion induced in the onlooker by the video clips. Thus, modulation of S1 activity contingent upon observation of others' pain and touch may reflect the mapping of sensory qualities of observed painful and tactile stimuli. Results indicate that the S1 is not only involved in the actual perception of pain and touch but also plays an important role in extracting somatic features from social interactions.

Despite the increasing interest in twin studies and the stunning amount of research on face recognition, the ability of adult identical twins to discriminate their own faces from those of their co-twins has been scarcely investigated. One's own face is the most distinctive feature of the bodily self, and people typically show a clear advantage in recognizing their own face even more than other very familiar identities. Given the very high level of resemblance of their faces, monozygotic twins represent a unique model for exploring self-face processing. Herein we examined the ability of monozygotic twins to distinguish their own face from the face of their co-twin and of a highly familiar individual. Results show that twins equally recognize their own face and their twin's face. This lack of self-face advantage was negatively predicted by how much they felt physically similar to their co-twin and by their anxious or avoidant attachment style. We speculate that in monozygotic twins, the visual representation of the self-face overlaps with that of the co-twin. Thus, to distinguish the self from the co-twin, monozygotic twins have to rely much more than control participants on the multisensory integration processes upon which the sense of bodily self is based. Moreover, in keeping with the notion that attachment style influences perception of self and significant others, we propose that the observed self/co-twin confusion may depend upon insecure attachment.