The body in the brain: neural bases of corporeal awareness

The Development of a Cross-Modal Sense of Body Ownership

In this study, we investigated the contribution of tactile and proprioceptive cues to the development of the sense of body ownership by testing the susceptibility of 4- to 5-year-old children, 8- to 9-year-old children, and adults to the somatic rubber-hand illusion (SRHI). We found that feelings of owning a rubber hand in the SHRI paradigm, as assessed by explicit reports (i.e., questionnaire), are already present by age 4 and do not change throughout development. In contrast, the effect of the illusion on the sense of hand position, as assessed by a pointing task, was present only in 8- to 9-year-old children and adults; the magnitude of such capture increased with age. Our findings reveal that tactile-proprioceptive interactions contributed differently to the two aspects characterizing the SRHI: Although the contribution of such interactions to an explicit sense of self was similar across age groups, their contribution to the more implicit recalibration of hand position is still developing by age 9.

Deliberate and spontaneous sensations of disembodiment: capacity or flaw?

INTRODUCTION

Hallucinations that involve shifts in the subjectively experienced location of the self, have been termed "out-of-body experiences" (OBEs). Early psychiatric accounts cast OBEs as a specific instance of depersonalisation and derealisation disorder (DPD-DR). However, during feelings of alienation and lack of body realism in DPD-DR the self is experienced within the physical body. Deliberate forms of "disembodiment" enable humans to imagine another's visuo-spatial perspective taking (VPT), thus, if a strong relationship between deliberate and spontaneous forms of disembodiment could be revealed, then uncontrolled OBEs could be "the other side of the coin" of a uniquely human capacity.

METHODS

We present a narrative review of behavioural and neuroimaging work emphasising methodological and theoretical aspects of OBE and VPT research and a potential relationship.

RESULTS

Results regarding a direct behavioural relationship between VPT and OBE are mixed and we discuss reasons by pointing out the importance of using realistic tasks and recruiting genuine OBEers instead of general DPD-DR patients. Furthermore, we review neuroimaging evidence showing overlapping neural substrates between VPT and OBE, providing a strong argument for a relationship between the two processes.

CONCLUSIONS

We conclude that OBE should be regarded as a necessary implication of VPT ability in humans, or even as a necessary and potentially sufficient condition for the evolution of VPT.

The Erasmus MC modifications to the (revised) Nottingham Sensory Assessment: a reliable somatosensory assessment measure for patients with intracranial disorders

Objective: To investigate the intra-rater and inter-rater reliability of the Erasmus MC modifications to the Nottingham Sensory Assessment (EmNSA).

Subjects: A consecutive sample of 18 inpatients, with a mean age of 57.7 years, diagnosed with an intracranial disorder and referred for physiotherapy.

Setting: The inpatient neurology and neurosurgery wards of a university hospital.

Design: Through discussions between four experienced neurophysiotherapists, the testing procedures of the revised Nottingham Sensory Assessment were further standardized. Subsequently, the intra-rater and inter-rater reliabilities of the EmNSA were investigated.

Results: The intra-rater reliability of the tactile sensations, sharp-blunt discrimination and the proprioception items of the EmNSA were generally good to excellent for both raters with a range of weighted kappa coefficients between 0.58 and 1.00. Likewise the inter-rater reliabilities of these items were predominantly good to excellent with a range of weighted kappa coefficients between 0.46 and 1.00. An exception was the two-point discrimination that had a poor to good reliability, with the range for intra-rater reliability of 0.11-0.63 and for inter-rater reliability -0.10-0.66.

Conclusion: The EmNSA is a reliable screening tool to evaluate primary somatosensory impairments in neurological and neurosurgical inpatients with intracranial disorders. Further research is necessary to consolidate these results and establish the validity and responsiveness of the Erasmus MC modifications to the NSA.

Selective functional connectivity abnormality of the transition zone of the inferior parietal lobule in schizophrenia

Structural and functional alterations in the inferior parietal lobule (IPL) in schizophrenia have been frequently reported; however, the IPL connectivity changes in schizophrenia remain largely unknown. Based on heterogeneity of the IPL in structure, connection and function, we hypothesize that the resting-state functional connectivities (rsFCs) of the IPL subregions are differentially affected in schizophrenia. This study included 95 schizophrenia patients and 104 healthy controls. The IPL subregions were defined according to a previous in vivo connection-based parcellation study. We calculated the rsFC of each IPL subregion and compared them between the two groups while controlling for the effects of age, gender, and grey matter volume. Among the six subregions of the left IPL and the five subregions of the right IPL, only the bilateral PFm (a transition zone of the IPL) subregions exhibited abnormal rsFC in schizophrenia. Specifically, the left PFm showed increased rsFC with the bilateral lingual gyri in schizophrenia patients than in healthy controls. The right PFm exhibited increased rsFC with the right lingual gyrus and inferior occipital gyrus, and bilateral mid-cingulate and sensorimotor cortices in schizophrenia patients. These findings suggest a selective rsFC abnormality in the IPL subregions in schizophrenia, characterized by the increased rsFC between the PFm subregion of the IPL and the visual and sensorimotor areas.

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Investigation of the subregional-level rsFC changes of the IPL in schizophrenia

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The PFm is only IPL subregion with significant rsFC changes in schizophrenia.

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Suggesting a selective rsFC abnormality in the IPL subregions in schizophrenia

Left caloric vestibular stimulation as a tool to reveal implicit and explicit parameters of body representation

Homeostatic parameters, such as temperature, are related to body representation. In this study, we measured whether caloric vestibular stimulation (CVS) alters body temperature and tactile processing, and if in the direction predicted by a holistic body matrix representation. Skin temperature and tactile two-point discrimination (TPD) acuity were measured for both arms before, immediately after and with a delay from CVS. Participants were also administered a personality questionnaire and an anxiety inventory to rule out confounding factors. Two control experiments were planned to exclude casual variations. Our results show that temperature drops significantly in both arms after CVS. CVS also induces a bilateral improvement in tactile acuity (even though not immediately after but in the delayed condition). Finally, these effects are not due to learning, as demonstrated by the control experiment. In summary, our results suggest that vestibular stimulation updates body representation, supporting the evidence in favor of a body matrix.

Spinal cord injury affects the interplay between visual and sensorimotor representations of the body

The brain integrates multiple sensory inputs, including somatosensory and visual inputs, to produce a representation of the body. Spinal cord injury (SCI) interrupts the communication between brain and body and the effects of this deafferentation on body representation are poorly understood. We investigated whether the relative weight of somatosensory and visual frames of reference for body representation is altered in individuals with incomplete or complete SCI (affecting lower limbs’ somatosensation), with respect to controls. To study the influence of afferent somatosensory information on body representation, participants verbally judged the laterality of rotated images of feet, hands, and whole-bodies (mental rotation task) in two different postures (participants’ body parts were hidden from view). We found that (i) complete SCI disrupts the influence of postural changes on the representation of the deafferented body parts (feet, but not hands) and (ii) regardless of posture, whole-body representation progressively deteriorates proportionally to SCI completeness. These results demonstrate that the cortical representation of the body is dynamic, responsive, and adaptable to contingent conditions, in that the role of somatosensation is altered and partially compensated with a change in the relative weight of somatosensory versus visual bodily representations.

Tool-use: An open window into body representation and its plasticity

Over the last decades, scientists have questioned the origin of the exquisite human mastery of tools. Seminal studies in monkeys, healthy participants and brain-damaged patients have primarily focused on the plastic changes that tool-use induces on spatial representations. More recently, we focused on the modifications tool-use must exert on the sensorimotor system and highlighted plastic changes at the level of the body representation used by the brain to control our movements, i.e., the Body Schema. Evidence is emerging for tool-use to affect also more visually and conceptually based representations of the body, such as the Body Image. Here we offer a critical review of the way different tool-use paradigms have been, and should be, used to try disentangling the critical features that are responsible for tool incorporation into different body representations. We will conclude that tool-use may offer a very valuable means to investigate high-order body representations and their plasticity.

Transcranial Electrical Stimulation in Post-Stroke Cognitive Rehabilitation

Abstract. Cognitive rehabilitation is an important area of neurological rehabilitation, which aims at the treatment of cognitive disorders due to acquired brain damage of different etiology, including stroke. Although the importance of cognitive rehabilitation for stroke survivors is well recognized, available cognitive treatments for neuropsychological disorders, such as spatial neglect, hemianopia, apraxia, and working memory, are overall still unsatisfactory. The growing body of evidence supporting the potential of the transcranial Electrical Stimulation (tES) as tool for interacting with neuroplasticity in the human brain, in turn for enhancing perceptual and cognitive functions, has obvious implications for the translation of this noninvasive brain stimulation technique into clinical settings, in particular for the development of tES as adjuvant tool for cognitive rehabilitation. The present review aims at presenting the current state of art concerning the use of tES for the improvement of post-stroke visual and cognitive deficits (except for aphasia and memory disorders), showing the therapeutic promises of this technique and offering some suggestions for the design of future clinical trials. Although this line of research is still in infancy, as compared to the progresses made in the last years in other neurorehabilitation domains, current findings appear very encouraging, supporting the development of tES for the treatment of post-stroke cognitive impairments.

Maladaptive change of body representation in the brain after damage to central or peripheral nervous system

Our brain has great flexibility to cope with various changes in the environment. Use-dependent plasticity, a kind of functional plasticity, plays the most important role in this ability to cope. For example, the functional recovery of paretic limb motor movement during post-stroke rehabilitation depends mainly on how much it is used. Patients with hemiparesis, however, tend to gradually disuse the paretic limb because of its motor impairment. Decreased use of the paretic hand then leads to further functional decline brought by use-dependent plasticity. To break this negative loop, body representation, which is the conscious and unconscious information regarding body state stored in the brain, is key for using the paretic limb because it plays an important role in selecting an effector while a motor program is generated. In an attempt to understand body representation in the brain, we reviewed animal and human literature mainly on the alterations of the sensory maps in the primary somatosensory cortex corresponding to the changes in limb usage caused by peripheral or central nervous system damage.

Increases in the right dorsolateral prefrontal cortex and decreases the rostral prefrontal cortex activation after-8 weeks of focused attention based mindfulness meditation

Mindfulness meditation is a form of attention control training. The training exercises the ability to repeatedly focus attention. We addressed the activation changes related to an 8-weeks mindfulness-oriented focused attention meditation training on an initially naïve subject cohort. Before and after training participants underwent an fMRI experiment, thus, although not strictly a cross over design, they served as their internal own control. During fMRI they exercised focused attention on breathing and body scan as compared to resting. We found increased and decreased activation in different parts of the prefrontal cortex (PFC) by comparing pre- vs. post-mindfulness training (MT) during breathing and body scan meditation exercises that were compared against their own resting state. In the post-MT (vs. pre-MT) meditation increased activation in the right dorsolateral PFC and in the left caudate/anterior insula and decreased activation in the rostral PFC and right parietal area 3b. Thus a brief mindfulness training caused increased activation in areas involved in sustaining and monitoring the focus of attention (dorsolateral PFC), consistent with the aim of mindfulness that is exercising focused attention mechanisms, and in the left caudate/anterior insula involved in attention and corporeal awareness and decreased activation in areas part of the "default mode" network and is involved in mentalizing (rostral PFC), consistent with the ability trained by mindfulness of reducing spontaneous mind wandering.

Phenomenology and neurobiology of self disorder in schizophrenia: Secondary factors

Schizophrenia is a diverse and varying syndrome that defies most attempts at classification and pathogenetic explanation. This is the second of two articles offering a comprehensive model meant to integrate an understanding of schizophrenia-related forms of subjectivity, especially anomalous core-self experience (disturbed ipseity), with neurocognitive and neurodevelopmental findings. Previously we discussed the primary or foundational role of disturbed intermodal perceptional integration ("perceptual dys-integration"). Here we discuss phenomenological alterations that can be considered secondary in a pathogenetic sense--whether as consequential products downstream from a more originary disruption, or as defensive reactions involving quasi-intentional or even volitional compensations to the more primary disruptions. These include secondary forms of: 1, hyperreflexivity, 2, diminished self-presence (self-affection), and 3. disturbed "rip" or "hold" on the cognitive/perceptual field of awareness. We consider complementary relations between these secondary abnormal experiences while also considering their temporal relationships and pathogenetic intertwining with the more primary phenomenological alterations discussed previously, all in relation to the neurodevelopmental model. The secondary phenomena can be understood as highly variable factors involving overall orientations or attitudes toward experience; they have some affinities with experiences of meditation, introspectionism, and depersonalization defense. Also, they seem likely to become more pronounced during adolescence as a result of new cognitive capacities related to development of the prefrontal lobes, especially attention allocation, executive functions, abstraction, and meta-awareness. Heterogeneity in these secondary alterations might help explain much of the clinical diversity in schizophrenia, both between patients and within individual patients over time--without however losing sight of key underlying commonalities.

Phenomenology and neurobiology of self disorder in schizophrenia: Primary factors

Schizophrenia is a heterogeneous syndrome, varying between persons and over course of illness. In this and a companion article, we argue that comprehension of this condition or set of conditions may require combining a phenomenological perspective emphasizing disorders of basic-self experience ("ipseity disturbance") with a multidimensional appreciation of possible neurobiological correlates--both primary and secondary. Previous attempts to link phenomenology and neurobiology generally focus on a single neurocognitive factor. We consider diverse aspects of schizophrenia in light of a diverse, albeit interacting, set of neurocognitive abnormalities, examining both synchronic (structural) interdependence and diachronic (temporal) succession. In this article we focus on the primary or foundational role of early perceptual and motoric disturbances that affect perceptual organization and especially intermodal or multisensory perceptual integration (“perceptual dys-integration”). These disturbances are discussed in terms of their implications for three interconnected aspects of selfhood in schizophrenia, primary forms of: disrupted "hold" or "grip" on the world, hyperreflexivity, diminished self-presence (self-affection). Disturbances of organization or integration imply forms of perceptual incoherence or diminished cognitive coordination. The effect is to disrupt one's ability to apprehend the world in holistic, vital, or contextually grounded fashion, or to fully identify with or experience the unity of one's own body or thinking--thereby generating an early and profound (albeit often subtle) disruption or diminishment of basic or core self and of the sense of existing in a coherent world. We discuss interrelationships or possible complementarities between these three aspects, and consider their relevance for a neurodevelopmental account of schizophrenia.

Visual Feedback of Tongue Movement for Novel Speech Sound Learning

Pronunciation training studies have yielded important information concerning the processing of audiovisual (AV) information. Second language (L2) learners show increased reliance on bottom-up, multimodal input for speech perception (compared to monolingual individuals). However, little is known about the role of viewing one's own speech articulation processes during speech training. The current study investigated whether real-time, visual feedback for tongue movement can improve a speaker's learning of non-native speech sounds. An interactive 3D tongue visualization system based on electromagnetic articulography (EMA) was used in a speech training experiment. Native speakers of American English produced a novel speech sound (/ɖ/; a voiced, coronal, palatal stop) before, during, and after trials in which they viewed their own speech movements using the 3D model. Talkers' productions were evaluated using kinematic (tongue-tip spatial positioning) and acoustic (burst spectra) measures. The results indicated a rapid gain in accuracy associated with visual feedback training. The findings are discussed with respect to neural models for multimodal speech processing.

Distinct contributions of extrastriate body area and temporoparietal junction in perceiving one's own and others' body

The right temporoparietal cortex plays a critical role in body representation. Here, we applied repetitive transcranial magnetic stimulation (rTMS) over right extrastriate body area (EBA) and temporoparietal junction (TPJ) to investigate their causative roles in perceptual representations of one's own and others' body. Healthy women adjusted size-distorted pictures of their own body or of the body of another person according to how they perceived the body (subjective task) or how others perceived it (intersubjective task). In keeping with previous reports, at baseline, we found an overall underestimation of body size. Crucially, EBA-rTMS increased the underestimation bias when participants adjusted the images according to how others perceived their own or the other woman's body, suggesting a specific role of EBA in allocentric body representations. Conversely, TPJ-rTMS increased the underestimation bias when participants adjusted the body of another person, either a familiar other or a close friend, in both subjective and intersubjective tasks, suggesting an involvement of TPJ in representing others' bodies. These effects were body-specific, since no TMS-induced modulation was observed when participants judged a familiar object. The results suggest that right EBA and TPJ play active and complementary roles in the complex interaction between the perceptions of one's own and other people's body.

The body and objects represented in the ventral stream of the parieto-premotor network

The network between the parietal cortex and premotor cortex has a pivotal role in sensory-motor control. Grasping-related neurons in the anterior intraparietal area (AIP) and the ventral premotor cortex (F5) showed complementary properties each other. The object information for grasping is sent from the parietal cortex to the premotor cortex for sensory-motor transformation, and the backward signal from the premotor cortex to parietal cortex can be considered an efference copy/corollary discharge that is used to predict sensory outcome during motor behavior. Mirror neurons that represent both own action and other's action are involved in this system. This system also very well fits with body schema that reflects online state of the body during motor execution. We speculate that the parieto-premotor network, which includes the mirror neuron system, is key for mapping one's own body and the bodies of others. This means that the neuronal substrates that control one's own action and the mirror neuron system are shared with the "who" system, which is related to the recognition of action contribution, i.e., sense of agency. Representation of own and other's body in the parieto-premotor network is key to link between sensory-motor control and higher-order cognitive functions.

Tactile Toe Agnosia and Percept of a "Missing Toe" in Healthy Humans

A disturbance of body representation is central to many neurological and psychiatric conditions, but the mechanisms by which body representations are constructed by the brain are not fully understood. We demonstrate a directional disturbance in tactile identification of the toes in healthy humans. Nineteen young adult participants underwent tactile stimulation of the digits with the eyes closed and verbally reported the identity of the stimulated digit. In the majority of individuals, responses to the second and third toes were significantly biased toward the laterally neighboring digit. The directional bias was greater for the nondominant foot and was affected by the identity of the immediately preceding stimulated toe. Unexpectedly, 9/19 participants reported the subjective experience of a "missing toe" or "missing space" during the protocol. These findings challenge current models of somatosensory localization, as they cannot be explained simply by a lack of distinct representations for toes compared with fingers, or by overt toe-finger correspondences. We present a novel theory of equal spatial representations of digit width combined with a "preceding neighbor" effect to explain the observed phenomena. The diagnostic implications for neurological disorders that involve "digit agnosia" are discussed.

Modulation of non-painful phantom sensation in subjects with spinal cord injury by means of rTMS

We aimed in this study to investigate whether repetitive transcranial magnetic stimulation (rTMS), given as theta burst stimulation (TBS), can interfere with non-painful phantom sensations in subjects with spinal cord injury (SCI). In double-blind, sham-controlled experiments in five subjects with cervical or thoracic traumatic SCI, we evaluated the effects of a single session of inhibitory (continuous) TBS, excitatory (intermittent) TBS, or placebo TBS, on simplex and complex non-painful phantom sensations. The interventions targeted the contralateral primary motor cortex (M1), the primary sensory cortex (S1) and the posterior parietal cortex (PPC). Measurements were carried out at baseline (T0), 5 min (T1) and 30 min later (T2) after the intervention. Descriptive evaluation of results shows that non-painful phantom sensations were not affected by rTMS applied over M1. Continuous (inhibitory) TBS over S1 induced a short-lasting decrease of simple non-painful phantom sensations, while continuous TBS over PPC induced a short-lasting decrease of both simple and complex phantom sensations. Intermittent (excitatory) TBS over PPC induced a slight increase of non-painful phantom sensations. Tests for significance confirm these observations, but must be interpreted with caution because of the small sample size. In conclusion, non-painful phantom sensations may be associated to a hyperexcitability of PPC and to a lesser extent of S1, which can be normalized by inhibitory rTMS. Our preliminary findings provide further evidence that neuromodulatory techniques are able to reverse phantom sensations not only after limb amputation but also in other conditions characterized by deafferentation such as SCI.

The somatic marker theory in the context of addiction: contributions to understanding development and maintenance

Recent theoretical accounts of addiction have acknowledged that addiction to substances and behaviors share inherent similarities (eg, insensitivity to future consequences and self-regulatory deficits). This recognition is corroborated by inquiries into the neurobiological correlates of addiction, which has indicated that different manifestations of addictive pathology share common neural mechanisms. This review of the literature will explore the feasibility of the somatic marker hypothesis as a unifying explanatory framework of the decision-making deficits that are believed to be involved in addiction development and maintenance. The somatic marker hypothesis provides a neuroanatomical and cognitive framework of decision making, which posits that decisional processes are biased toward long-term prospects by emotional marker signals engendered by a neuronal architecture comprising both cortical and subcortical circuits. Addicts display markedly impulsive and compulsive behavioral patterns that might be understood as manifestations of decision-making processes that fail to take into account the long-term consequences of actions. Evidence demonstrates that substance dependence, pathological gambling, and Internet addiction are characterized by structural and functional abnormalities in neural regions, as outlined by the somatic marker hypothesis. Furthermore, both substance dependents and behavioral addicts show similar impairments on a measure of decision making that is sensitive to somatic marker functioning. The decision-making deficits that characterize addiction might exist a priori to addiction development; however, they may be worsened by ingestion of substances with neurotoxic properties. It is concluded that the somatic marker model of addiction contributes a plausible account of the underlying neurobiology of decision-making deficits in addictive disorders that is supported by the current neuroimaging and behavioral evidence. Implications for future research are outlined.

Disentangling interoception: insights from focal strokes affecting the perception of external and internal milieus

Interoception is the moment-to-moment sensing of the physiological condition of the body. The multimodal sources of interoception can be classified into two different streams of afferents: an internal pathway of signals arising from core structures (i.e., heart, blood vessels, and bronchi) and an external pathway of body-mapped sensations (i.e., chemosensation and pain) arising from peripersonal space. This study examines differential processing along these streams within the insular cortex (IC) and their subcortical tracts connecting frontotemporal networks. Two rare patients presenting focal lesions of the IC (insular lesion, IL) or its subcortical tracts (subcortical lesion, SL) were tested. Internally generated interoceptive streams were assessed through a heartbeat detection (HBD) task, while those externally triggered were tapped via taste, smell, and pain recognition tasks. A differential pattern was observed. The IC patient showed impaired internal signal processing while the SL patient exhibited external perception deficits. Such selective deficits remained even when comparing each patient with a group of healthy controls and a group of brain-damaged patients. These outcomes suggest the existence of distinguishable interoceptive streams. Results are discussed in relation with neuroanatomical substrates, involving a fronto-insulo-temporal network for interoceptive and cognitive contextual integration.

Losing track of time through delayed body representations

The ability to keep track of time is perceived as crucial in most human societies. However, to lose track of time may also serve an important social role, associated with recreational purpose. To this end a number of social technologies are employed, some of which may relate to a manipulation of time perception through a modulation of body representation. Here, we investigated an influence of real-time or delayed videos of own-body representations on time perception in an experimental setup with virtual mirrors. Seventy participants were asked to either stay in the installation until they thought that a defined time (90 s) had passed, or they were encouraged to stay in the installation as long as they wanted and after exiting were asked to estimate the duration of their stay. Results show that a modulation of body representation by time-delayed representations of the mirror-video displays influenced time perception. Furthermore, these time-delayed conditions were associated with a greater sense of arousal and intoxication. We suggest that feeding in references to the immediate past into working memory could be the underlying mental mechanism mediating the observed modulation of time perception. We argue that such an influence on time perception would probably not only be achieved visually, but might also work with acoustic references to the immediate past (e.g., with music).

How Kinesthetic Motor Imagery works: a predictive-processing theory of visualization in sports and motor expertise

Kinesthetic Motor Imagery (KMI) is an important technique to acquire and refine motor skills. KMI is widely used by professional athletes as an effective way to improve motor performance without overt motor output. Despite this obvious relevance, the functional mechanisms and neural circuits involved in KMI in sports are still poorly understood. In the present article, which aims at bridging the sport sciences and cognitive neurophysiology literatures, we give a brief overview of relevant research in the field of KMI. Furthermore, we develop a theoretical account that relates KMI to predictive motor control theories assuming that it is based on internal activation of anticipatory images of action effects. This mechanism allows improving motor performance solely based on internal emulation of action. In accordance with previous literature, we propose that this emulation mechanism is implemented in brain regions that partially overlap with brain areas involved in overt motor performance including the posterior parietal cortex, the cerebellum, the basal ganglia and the premotor cortex. Finally, we outline one way to test the heuristic value of our theoretical framework for KMI; we suggest that experience with motor performance improves the ability to correctly infer the goals of others, in particular in penalty blocking in soccer.

Revisiting the body-schema concept in the context of whole-body postural-focal dynamics

The body-schema concept is revisited in the context of embodied cognition, further developing the theory formulated by Marc Jeannerod that the motor system is part of a simulation network related to action, whose function is not only to shape the motor system for preparing an action (either overt or covert) but also to provide the self with information on the feasibility and the meaning of potential actions. The proposed computational formulation is based on a dynamical system approach, which is linked to an extension of the equilibrium-point hypothesis, called Passive Motor Paradigm: this dynamical system generates goal-oriented, spatio-temporal, sensorimotor patterns, integrating a direct and inverse internal model in a multi-referential framework. The purpose of such computational model is to operate at the same time as a general synergy formation machinery for planning whole-body actions in humanoid robots and/or for predicting coordinated sensory-motor patterns in human movements. In order to illustrate the computational approach, the integration of simultaneous, even partially conflicting tasks will be analyzed in some detail with regard to postural-focal dynamics, which can be defined as the fusion of a focal task, namely reaching a target with the whole-body, and a postural task, namely maintaining overall stability.

Crossing the hands increases illusory self-touch

Manipulation of hand posture, such as crossing the hands, has been frequently used to study how the body and its immediately surrounding space are represented in the brain. Abundant data show that crossed arms posture impairs remapping of tactile stimuli from somatotopic to external space reference frame and deteriorates performance on several tactile processing tasks. Here we investigated how impaired tactile remapping affects the illusory self-touch, induced by the non-visual variant of the rubber hand illusion (RHI) paradigm. In this paradigm blindfolded participants (Experiment 1) had their hands either uncrossed or crossed over the body midline. The strength of illusory self-touch was measured with questionnaire ratings and proprioceptive drift. Our results showed that, during synchronous tactile stimulation, the strength of illusory self-touch increased when hands were crossed compared to the uncrossed posture. Follow-up experiments showed that the increase in illusion strength was not related to unfamiliar hand position (Experiment 2) and that it was equally strengthened regardless of where in the peripersonal space the hands were crossed (Experiment 3). However, while the boosting effect of crossing the hands was evident from subjective ratings, the proprioceptive drift was not modulated by crossed posture. Finally, in contrast to the illusion increase in the non-visual RHI, the crossed hand postures did not alter illusory ownership or proprioceptive drift in the classical, visuo-tactile version of RHI (Experiment 4). We argue that the increase in illusory self-touch is related to misalignment of somatotopic and external reference frames and consequently inadequate tactile-proprioceptive integration, leading to re-weighting of the tactile and proprioceptive signals.The present study not only shows that illusory self-touch can be induced by crossing the hands, but importantly, that this posture is associated with a stronger illusion.

Enfacing others but only if they are nice to you

Experiencing tactile facial stimulation while seeing synchronous stimuli on the face of another individual induces “enfacement,” i.e., the subjective illusory experience of ownership of the other's face (explicit measure) and the attribution of the others' facial features to one's own face (implicit measure). Here we expanded previous knowledge by investigating if the tendency to include the other into one's own representation is influenced by positive or negative interpersonal attitudes derived either from consolidated socio-cultural stereotypes or from newly acquired, short-term individual interactions with a specific person. To this aim, we tested in Caucasian white participants the enfacement with a white and a black confederate, before and after an experimental procedure inducing a positive or negative perception of each of them. The results show that the subjective experience of enfacement with in- and out-group others before and after the manipulation is similar. The bias in attributing other's facial features to one's own face after synchronous stroking was, instead, dependent on whether the other person was positively perceived, independently of his/her ethnicity. Thus, we show that realistic positive face-to-face interactions are more effective than consolidated racial biases in influencing the strength of self-attribution of another persons' facial features in the context of multisensory illusions. Results suggest that positive interpersonal interactions might powerfully change the plasticity of self-other representations.

The effect of visual magnification and reduction on perceived hand size

The aim of the present study was to clarify the mechanisms underlying body understanding by examining the impact of visual experience (magnification and reduction) on perception of hand size and neutral external objects (squares). Independent groups of participants were asked to look through a 2× magnification lens, a ½-× reduction lens, or a control UV filter and to make visual size judgments about square stimuli and their hands. In Experiment 1, participants used a measuring device with unmarked wooden slats orientated in horizontal and radial/vertical space for their visual judgments. In Experiment 2, participants used an upright frontal slat for visual length judgments of their hands to eliminate any potential foreshortening in viewing the measurement apparatus. The results from the two experiments demonstrate that participants significantly underestimated both the square stimuli and their hands when they viewed them under a reduction lens. While overestimation and underestimation of squares was found for females in Experiment 2, males generally underestimated the squares. However, overestimation was not seen when the participants viewed their hands under a magnification lens. Implications of these findings are discussed.

Arousal responses to noxious stimuli in somatoparaphrenia and anosognosia: clues to body awareness

A complex brain representation of our body allows us to monitor incoming sensory stimuli and plan actions towards the external world. A critical element of such a complex representation is the sense of ownership towards our own body parts. Brain damage may disrupt this representation, leading to the striking neuropsychological condition called somatoparaphrenia, that is, the delusion that one's own limbs belong to someone else. The clinical features characterizing somatoparaphrenia are well known, however, physiological clues of the level at which this condition may disrupt sensory functions are unknown. In the present study we investigated this issue by measuring the anticipatory skin conductance response to noxious stimuli approaching either the affected or the intact body side in a group of patients with somatoparaphrenia (n=5; three females, age range=66-84), and in a group of patients with anosognosia for sensory deficits, i.e. preserved ownership but decreased awareness of somatosensory deficit, (n=5; one female, age range=62-81 years) and in a group of purely hemiplegic patients (n=5; two females, age range=63-74 years) with no deficits of ownership or sensory awareness. Results show that anticipatory skin conductance responses to noxious stimuli directed to the contralesional hand are significantly reduced as compared to noxious stimuli directed to the ipsilesional hand in patients with somatoparaphrenia. By contrast a non-reduced anticipatory skin conductance response was observed in control participants as well as in patients affected by anosognosia for the somatosensory deficit and in patients affected by pure motor deficits. Furthermore, a pain anticipation response was always measured when the stimuli were directed towards the ipsilesional, unaffected hand in all groups. Our results show for the first time that the delusions shown by somatoparaphrenic patients are associated with an altered physiological index of perceptual analysis. The reduced response to sensory threats approaching the body suggests a deep detachment of the affected body part from the patient's body representation. Conversely, normal reactions to incoming threats are found in the presence of impaired sensory awareness but intact body ownership, supporting the notion that representation of the body may be affected at different levels following brain damage.

Crossmodal representation of a functional robotic hand arises after extensive training in healthy participants

The way in which humans represent their own bodies is critical in guiding their interactions with the environment. To achieve successful body-space interactions, the body representation is strictly connected with that of the space immediately surrounding it through efficient visuo-tactile crossmodal integration. Such a body-space integrated representation is not fixed, but can be dynamically modulated by the use of external tools. Our study aims to explore the effect of using a complex tool, namely a functional prosthesis, on crossmodal visuo-tactile spatial interactions in healthy participants. By using the crossmodal visuo-tactile congruency paradigm, we found that prolonged training with a mechanical hand capable of distal hand movements and providing sensory feedback induces a pattern of interference, which is not observed after a brief training, between visual stimuli close to the prosthesis and touches on the body. These results suggest that after extensive, but not short, training the functional prosthesis acquires a visuo-tactile crossmodal representation akin to real limbs. This finding adds to previous evidence for the embodiment of functional prostheses in amputees, and shows that their use may also improve the crossmodal combination of somatosensory feedback delivered by the prosthesis with visual stimuli in the space around it, thus effectively augmenting the patients' visuomotor abilities.

Right supramarginal gyrus is crucial to overcome emotional egocentricity bias in social judgments

Humans tend to use the self as a reference point to perceive the world and gain information about other people's mental states. However, applying such a self-referential projection mechanism in situations where it is inappropriate can result in egocentrically biased judgments. To assess egocentricity bias in the emotional domain (EEB), we developed a novel visuo-tactile paradigm assessing the degree to which empathic judgments are biased by one's own emotions if they are incongruent to those of the person we empathize with. A first behavioral experiment confirmed the existence of such EEB, and two independent fMRI experiments revealed that overcoming biased empathic judgments is associated with increased activation in the right supramarginal gyrus (rSMG), in a location distinct from activations in right temporoparietal junction reported in previous social cognition studies. Using temporary disruption of rSMG with repetitive transcranial magnetic stimulation resulted in a substantial increase of EEB, and so did reducing visuo-tactile stimulation time as shown in an additional behavioral experiment. Our findings provide converging evidence from multiple methods and experiments that rSMG is crucial for overcoming emotional egocentricity. Effective connectivity analyses suggest that this may be achieved by early perceptual regulation processes disambiguating proprioceptive first-person information (touch) from exteroceptive third-person information (vision) during incongruency between self- and other-related affective states. Our study extends previous models of social cognition. It shows that although shared neural networks may underlie emotional understanding in some situations, an additional mechanism subserved by rSMG is needed to avoid biased social judgments in other situations.

Diverse spatial reference frames of vestibular signals in parietal cortex

Reference frames are important for understanding how sensory cues from different modalities are coordinated to guide behavior, and the parietal cortex is critical to these functions. We compare reference frames of vestibular self-motion signals in the ventral intraparietal area (VIP), parietoinsular vestibular cortex (PIVC), and dorsal medial superior temporal area (MSTd). Vestibular heading tuning in VIP is invariant to changes in both eye and head positions, indicating a body (or world)-centered reference frame. Vestibular signals in PIVC have reference frames that are intermediate between head and body centered. In contrast, MSTd neurons show reference frames between head and eye centered but not body centered. Eye and head position gain fields were strongest in MSTd and weakest in PIVC. Our findings reveal distinct spatial reference frames for representing vestibular signals and pose new challenges for understanding the respective roles of these areas in potentially diverse vestibular functions.

Revealing the invisible: the paradox of picturing a phantom limb

Illustrations of phantom limbs are intriguing as they depict an invisible perception. But such illustrations are also important: they provide a form of objectivity to phenomena, which particularly in the past, have often stretched credulity. Acknowledging the paradox of using images to reveal an absent though sensate body part, depictions of phantom limbs are discussed from the neurological perspective, starting with medieval pictures that showed the miraculous restoration of limbs, and which possibly represented pictorial metaphors for a phantom limb. Centuries later, phantom limbs-whether resulting from amputation or deafferentation-became illustrated, and some reasons for their illustration are considered. Although often depicted by others, the most precise and perhaps revealing illustrations of these phantoms have been those made when patients guide the artist, or draw the phantom themselves. In the case of phantom pains, the painful component too is sometimes illustrated, again, as with the miraculous, in metaphorical terms. More recently, depictions of phantoms have also been revealing in studies of some underlying mechanisms of phantom phenomena, notably in demonstrating novel patterns of referred sensations after amputation and attributable to cortical plasticity. Mention is made of photographs of phantom hands visualized using a mirror box, such visualization recalling full circle the miraculous restoration of limbs pictured in the past. The nature of the outline of the phantom is included in a discussion of demarcation of an invisible body part, before concluding that images of phantom limbs provide an invaluable background to understanding and studying these remarkable sensory phenomena.

Illusory ownership of a virtual child body causes overestimation of object sizes and implicit attitude changes

An illusory sensation of ownership over a surrogate limb or whole body can be induced through specific forms of multisensory stimulation, such as synchronous visuotactile tapping on the hidden real and visible rubber hand in the rubber hand illusion. Such methods have been used to induce ownership over a manikin and a virtual body that substitute the real body, as seen from first-person perspective, through a head-mounted display. However, the perceptual and behavioral consequences of such transformed body ownership have hardly been explored. In Exp. 1, immersive virtual reality was used to embody 30 adults as a 4-y-old child (condition C), and as an adult body scaled to the same height as the child (condition A), experienced from the first-person perspective, and with virtual and real body movements synchronized. The result was a strong body-ownership illusion equally for C and A. Moreover there was an overestimation of the sizes of objects compared with a nonembodied baseline, which was significantly greater for C compared with A. An implicit association test showed that C resulted in significantly faster reaction times for the classification of self with child-like compared with adult-like attributes. Exp. 2 with an additional 16 participants extinguished the ownership illusion by using visuomotor asynchrony, with all else equal. The size-estimation and implicit association test differences between C and A were also extinguished. We conclude that there are perceptual and probably behavioral correlates of body-ownership illusions that occur as a function of the type of body in which embodiment occurs.

Tool-use reshapes the boundaries of body and peripersonal space representations

Interaction with objects in the environment typically requires integrating information concerning the object location with the position and size of body parts. The former information is coded in a multisensory representation of the space around the body, a representation of peripersonal space (PPS), whereas the latter is enabled by an online, constantly updated, action-orientated multisensory representation of the body (BR). Using a tool to act upon relatively distant objects extends PPS representation. This effect has been interpreted as indicating that tools can be incorporated into BR. However, empirical data showing that tool-use simultaneously affects PPS representation and BR are lacking. To study this issue, we assessed the extent of PPS representation by means of an audio-tactile interaction task and BR by means of a tactile distance perception task and a body-landmarks localisation task, before and after using a 1-m-long tool to reach far objects. Tool-use extended the representation of PPS along the tool axis and concurrently shaped BR; after tool-use, subjects perceived their forearm narrower and longer compared to before tool-use, a shape more similar to the one of the tool. Tool-use was necessary to induce these effects, since a pointing task did not affect PPS and BR. These results show that a brief training with a tool induces plastic changes both to the perceived dimensions of the body part acting upon the tool and to the space around it, suggesting a strong overlap between peripersonal space and body representation.

The embodied mind extended: using words as social tools

The extended mind view and the embodied-grounded view of cognition and language are typically considered as rather independent perspectives. In this paper we propose a possible integration of the two views and support it proposing the idea of “Words As social Tools” (WAT). In this respect, we will propose that words, also due to their social and public character, can be conceived as quasi-external devices that extend our cognition. Moreover, words function like tools in that they enlarge the bodily space of action thus modifying our sense of body. To support our proposal, we review the relevant literature on tool-use and on words as tools and report recent evidence indicating that word use leads to an extension of space close to the body. In addition, we outline a model of the neural processes that may underpin bodily space extension via word use and may reflect possible effects on cognition of the use of words as external means. We also discuss how reconciling the two perspectives can help to overcome the limitations they encounter if considered independently.

Motor and parietal cortex stimulation for phantom limb pain and sensations

Limb amputation may lead to chronic painful sensations referred to the absent limb, ie phantom limb pain (PLP), which is likely subtended by maladaptive plasticity. The present study investigated whether transcranial direct current stimulation (tDCS), a noninvasive technique of brain stimulation that can modulate neuroplasticity, can reduce PLP. In 2 double-blind, sham-controlled experiments in subjects with unilateral lower or upper limb amputation, we measured the effects of a single session of tDCS (2 mA, 15 min) of the primary motor cortex (M1) and of the posterior parietal cortex (PPC) on PLP, stump pain, nonpainful phantom limb sensations and telescoping. Anodal tDCS of M1 induced a selective short-lasting decrease of PLP, whereas cathodal tDCS of PPC induced a selective short-lasting decrease of nonpainful phantom sensations; stump pain and telescoping were not affected by parietal or by motor tDCS. These findings demonstrate that painful and nonpainful phantom limb sensations are dissociable phenomena. PLP is associated primarily with cortical excitability shifts in the sensorimotor network; increasing excitability in this system by anodal tDCS has an antalgic effect on PLP. Conversely, nonpainful phantom sensations are associated to a hyperexcitation of PPC that can be normalized by cathodal tDCS. This evidence highlights the relationship between the level of excitability of different cortical areas, which underpins maladaptive plasticity following limb amputation and the phenomenology of phantom limb, and it opens up new opportunities for the use of tDCS in the treatment of PLP.

The effect of limb crossing and limb congruency on multisensory integration in peripersonal space for the upper and lower extremities

The present study investigated how multisensory integration in peripersonal space is modulated by limb posture (i.e. whether the limbs are crossed or uncrossed) and limb congruency (i.e. whether the observed body part matches the actual position of one's limb). This was done separately for the upper limbs (Experiment 1) and the lower limbs (Experiment 2). The crossmodal congruency task was used to measure peripersonal space integration for the hands and the feet. It was found that the peripersonal space representation for the hands but not for the feet is dynamically updated based on both limb posture and limb congruency. Together these findings show how dynamic cues from vision, proprioception, and touch are integrated in peripersonal limb space and highlight fundamental differences in the way in which peripersonal space is represented for the upper and lower extremity.

The rubber hand illusion in complex regional pain syndrome: preserved ability to integrate a rubber hand indicates intact multisensory integration

In patients with complex regional pain syndrome (CRPS) type 1, processing of static tactile stimuli is impaired, whereas more complex sensory integration functions appear preserved. This study investigated higher order multisensory integration of body-relevant stimuli using the rubber hand illusion in CRPS patients. Subjective self-reports and skin conductance responses to watching the rubber hand being harmed were compared among CRPS patients (N=24), patients with upper limb pain of other origin (N=21, clinical control group), and healthy subjects (N=24). Additionally, the influence of body representation (body plasticity [Trinity Assessment of Body Plasticity], neglect-like severity symptoms), and clinical signs of illusion strength were investigated. For statistical analysis, 1-way analysis of variance, t test, Pearson correlation, with α=0.05 were used. CRPS patients did not differ from healthy subjects and the control group with regard to their illusion strength as assessed by subjective reports or skin conductance response values. Stronger left-sided rubber hand illusions were reported by healthy subjects and left-side-affected CRPS patients. Moreover, for this subgroup, illness duration and illusion strength were negatively correlated. Overall, severity of neglect-like symptoms and clinical signs were not related to illusion strength. However, patients with CRPS of the right hand reported significantly stronger neglect-like symptoms and significantly lower illusion strength of the affected hand than patients with CRPS of the left hand. The weaker illusion of CRPS patients with strong neglect-like symptoms on the affected hand supports the role of top-down processes modulating body ownership. Moreover, the intact ability to perceive illusory ownership confirms the notion that, despite impaired processing of proprioceptive or tactile input, higher order multisensory integration is unaffected in CRPS.