Behavioral and Physiological Evidence of a favored Hand Posture in the Body Representation for Action.

Motor planning and execution require a representational map of our body. Since the body can assume different postures, it is not known how it is represented in this map. Moreover, is the generation of the motor command favored by some body configurations? We investigated the existence of a centrally favored posture of the hand for action, in search of physiological and behavioral advantages due to central motor processing. We tested two opposite hand pinch grips, equally difficult and commonly used: forearm pronated, thumb-down, index-up pinch against the same grip performed with thumb-up. The former revealed faster movement onset, sign of faster neural computation, and faster target reaching. It induced increased corticospinal excitability, independently on pre-stimulus tonic muscle contraction. Remarkably, motor excitability also increased when thumb-down pinch was only observed, imagined, or prepared, actually keeping the hand at rest. Motor advantages were independent of any concurrent modulation due to somatosensory input, as shown by testing afferent inhibition. Results provide strong behavioral and physiological evidence for a preferred hand posture favoring brain motor control, independently by somatosensory processing. This suggests the existence of a baseline postural representation that may serve as an a priori spatial reference for body-space interaction.

Body-Space Interactions: Same Spatial Encoding but Different Influence of Valence for Reaching and Defensive Purposes.

The space around our body, the so-called peripersonal space, is where interactions with nearby objects may occur. "Defensive space" and "Reaching space", respectively, refer to two opposite poles of interaction between our body and the external environment: protecting the body and performing a goal-directed action. Here, we hypothesized that mechanisms underlying these two action spaces are differentially modulated by the valence of visual stimuli, as stimuli with negative valence are more likely to activate protective actions whereas stimuli with positive valence may activate approaching actions. To test whether such distinction in cognitive/evaluative processing exists between Reaching and Defensive spaces, we measured behavioral responses as well as neural activations over sensorimotor cortex using EEG while participants performed several tasks designed to tap into mechanisms underlying either Defensive (e.g., respond to touch) or Reaching space (e.g., estimate whether object is within reaching distance). During each task, pictures of objects with either positive or negative valence were presented at different distances from the participants' body. We found that Defensive space was smaller for positively compared with negatively valenced visual stimuli. Furthermore, sensorimotor cortex activation (reflected in modulation of beta power) during tactile processing was enhanced when coupled with negatively rather than positively valenced visual stimuli regarding Defensive space. On the contrary, both the EEG and behavioral measures capturing the mechanisms underlying Reaching space did not reveal any modulation by valence. Thus, although valence encoding had differential effects on Reaching and Defensive spaces, the distance of the visual stimulus modulated behavioral measures as well as activity over sensorimotor cortex (reflected in modulations of mu power) in a similar way for both types of spaces. Our results are compatible with the idea that Reaching and Defensive spaces involve the same distance-dependent neural representations of sensory input, whereas task goals and stimulus valence (i.e., contextual information) are implemented at a later processing stage and exert an influence on motor output rather than sensory/space encoding.

No efficacy of transcranial direct current stimulation on chronic migraine with medication overuse: A double blind, randomised clinical trial.

BACKGROUND: Transcranial direct current stimulation was suggested to provide beneficial effects in chronic migraine, a condition often associated with medication overuse for which no long-term therapy is available. METHODS: We conducted a randomised controlled trial to assess long-term efficacy of transcranial direct current stimulation. Adults diagnosed with chronic migraine and medication overuse were assigned to receive in a 1:1:1 ratio anodal, cathodal, or sham transcranial direct current stimulation daily for five consecutive days, along with standardised drug withdrawal protocol. Primary outcome was 50% reduction of days of headache per month at 12 months. Co-secondary outcomes were 50% reduction of days of headache per month at 6 months, reduction of analgesic intake per month, and change in disability and quality of life, catastrophising, depression, state and trait anxiety, dependence attitude and allodynia intensity. Patients were not allowed to take any migraine prophylaxis drug for the entire study period. RESULTS: We randomly allocated 135 patients to anodal (44), cathodal (45), and sham (46) transcranial direct current stimulation. At 6 and 12 months, the percentage of reduction of days of headache and number of analgesics per month ranged between 48.5% and 64.7%, without differences between transcranial direct current stimulation (cathodal, anodal, or the results obtained from the two arms of treatment, anodal plus cathodal) and sham. Catastrophising attitude significantly reduced at 12 months in all groups. There was no difference for the other secondary outcomes. CONCLUSIONS: Transcranial direct current stimulation did not influence the short and long-term course of chronic migraine with medication overuse after acute drug withdrawal. Behavioral and educational measures and support for patients' pain management could provide long-term improvement and low relapse rate.Trial registration number NCT04228809.

Body illusion and affordances: the influence of body representation on a walking imagery task in virtual reality.

It is well known that our body works as a fundamental reference when we perform visuo-perceptual judgements in spatial surroundings, and that body illusions can modify our perception of size and distance of objects in space. To date, however, few studies have evaluated whether or not a body illusion could have a significant impact on the way individuals perceive to move within the environment. Here, we used a full-body illusion paradigm to verify the hypothesis that an altered representation of the legs of the individuals influences their time-to-walk estimation while imaging to reach objects in a virtual environment. To do so, we asked a group of young healthy volunteers to perform a task in which they were required to imagine walking towards a previously seen target location in a virtual environment, soon after receiving the body illusion; we required participants to use a response button to time their imagined walk from start to end. We found that participants imagined walking faster following the illusion elicited by the vision of longer legs presented from an anatomical perspective, as compared to when experiencing standard legs in the same position.This difference in imagined walking distance decreased when the object to reach was displayed farther, suggesting a fading effect. Furthermore, taking into consideration the baseline error in walking time estimation in VR, we noticed a specific influence of the long anatomical legs in reducing the perceived time needed to reach an object and a general increase in the percentage of error when the same legs are presented in a non-anatomical orientation. These findings provide evidence that body illusions could influence the way individuals perceive their locomotion in the spatial surrounding.

Somatosensory cortical representation of the body size.

The knowledge of the size of our own body parts is essential for accurately moving in space and efficiently interact with objects. A distorted perceptual representation of the body size often represents a core diagnostic criterion for some psychopathological conditions. The metric representation of the body was shown to depend on somatosensory afferences: local deafferentation indeed causes a perceptual distortion of the size of the anesthetized body part. A specular effect can be induced by altering the cortical map of body parts in the primary somatosensory cortex. Indeed, the present study demonstrates, in healthy adult participants, that repetitive Transcranial Magnetic Stimulation to the somatosensory cortical map of the hand in both hemispheres causes a perceptual distortion (i.e., an overestimation) of the size of the participants' own hand (Experiments 1-3), which does not involve other body parts (i.e., the foot, Experiment 2). Instead, the stimulation of the inferior parietal lobule of both hemispheres does not affect the perception of the own body size (Experiment 4). These results highlight the role of the primary somatosensory cortex in the building up and updating of the metric of body parts: somatosensory cortical activity not only shapes our somatosensation, it also affects how we perceive the dimension of our body.

Different tool training induces specific effects on body metric representation.

Morphology and functional aspects of the tool have been proposed to be critical factors modulating tool use-induced plasticity. However, how these aspects contribute to changing body representation has been underinvestigated. In the arm bisection task, participants have to estimate the length of their own arm by indicating its midpoint, a paradigm used to investigate the representation of the metric properties of the body. We employed this paradigm to investigate the impact of different actions onto tool embodiment. Our findings suggest that a training requiring actions mostly with proximal (shoulder) or distal (wrist) parts induces a different shift in the perceived arm midpoint. This effect is independent of, but enhanced by, the use of the tool during the training and in part influenced by specific demands of the task. These results suggest that specific motor patterns required by the training can induce different changes of body representation, calling for rethinking the concept of tool embodiment, which would be characterized not simply by the morphology of the tools, but also by the actions required for their specific use.

Roles of the right temporo-parietal and premotor cortices in self-location and body ownership.

In the rubber hand illusion (RHI), the feeling that a fake hand belongs to oneself can be induced by the simultaneous, congruent touch of the fake visible hand and one's own hidden hand. This condition is also associated with a recalibration of the perceived location of the real hand. A cortical network, including premotor and temporo-parietal areas, has been proposed as the basis of the RHI. However, the causal contribution of these areas to the discrete illusory components remains unclear. We used transcranial direct current stimulation (tDCS) to assess the contribution of the right premotor cortex (rPMc) and the right temporo-parietal junction (rTPJ) to the RHI and explored the role of these areas in modulating the subjective experience of embodiment and the misperception of the hand position. We found that anodal tDCS of both rPMc and rTPJ increased the misjudgement of the real hand location towards the fake hand. Crucially, the difference in proprioceptive displacement evoked by the congruent and incongruent visuo-tactile stroking was minimised when tDCS was applied over the rPMc, while it was amplified when the rTPJ was targeted. The parietal effects of tDCS also extended to the self-report components of the RHI. These findings suggest that the tDCS of rTPJ modulates the RHI depending on the temporal congruency of the visuo-tactile stimulation, while the tDCS of rPMc induces a general recalibration of hand coordinates, regardless of the visuo-tactile congruency. The present results are discussed in the view of a multicomponent model of the RHI.

More far is more right: Manual and ocular line bisections, but not the Judd illusion, depend on radial space.

Line bisection studies generally find a left-to-right shift in bisection bias with increasing distance between the observer and the target line, which may be explained by hemispheric differences in the processing of proximo-distal information. In the present study, the segregation between near and far space was further characterized across the motor system and contextual cues. To this aim, 20 right-handed participants were required to perform a manual bisection task of simple lines presented at three different distances (60, 90, 120 cm). Importantly, the horizontal spatial location of the line was manipulated along with the viewing distance to investigate more deeply the hemispheric engagement in the transition from near to far space. As the motoric component of the manual task producing activations of left premotor and motor areas may be partially responsible for the observed transition, participants were also involved in an ocular bisection task. Further, participants were required to bisect Judd variants of the target lines, which are known to elicit a Müller-Lyer-type illusion. Since the Judd illusion depends on areas in the ventral visual stream, we predicted that line bisections of Judd-type lines would be unaffected by viewing distance. Results showed that manual bisection of simple lines was modulated separately by viewing distance and the hemispace of presentation, with this pattern being similar for ocular bisection. Critically, bisections in the Judd illusion task were not modulated by viewing distance, whether performed by hand or by eye. Overall, these findings support the hypothesis that the right hemisphere plays a dominant role in the processing of space close to the body. They also present novel evidence for a general reduction of this dominance at farther distances, whether hand motor actions are involved or not. Finally, our study documents a dissociation between the processing of pure visuospatial information and that of a visual illusion as a function of viewing distance, supporting more generally the dorsal/near space and the ventral/far space segregation.

The contribution of response conflict, multisensory integration, and body-mediated attention to the crossmodal congruency effect.

The crossmodal congruency task is a consolidated paradigm for investigating interactions between vision and touch. In this task, participants judge the elevation of a tactile target stimulus while ignoring a visual distracter stimulus that may occur at a congruent or incongruent elevation, thus engendering a measure of visuo-tactile interference (crossmodal congruency effect, CCE). The CCE reflects perceptual, attentional, and response-related factors, but their respective roles and interactions have not been set out yet. In two experiments, we used the original version of the crossmodal congruency task as well as ad hoc manipulations of the experimental setting and of the participants' posture for characterizing the contributions of multisensory integration, body-mediated attention, and response conflict to the CCE. Results of the two experiments consistently showed that the largest amount of variance in the CCE is explained by the reciprocal elevation of visual and tactile stimuli. This finding is compatible with a major role of response conflict for the CCE. Weaker yet distinguishable contributions come from multisensory integration, observed in the absence of response conflict, and from hand-mediated attentional binding, observed with the modified posture and in the presence of response conflict. Overall, this study informs the long-standing debate about mechanisms underlying the CCE by revealing that the visuo-tactile interference in this task is primarily due to the competition between opposite response tendencies, with an additional contribution of multisensory integration and hand-mediated attentional binding.

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.

Grasping with the foot: goal and motor expertise in action observation.

Action observation typically induces an online inner simulation of the observed movements. Here we investigate whether action observation merely activates, in the observer, the muscles involved in the observed movement or also muscles that are typically used to achieve the observed action goal. In a first experiment, hand and foot motor areas were stimulated by means of transcranial magnetic stimulation, while participants viewed a typical hand action (grasping) or a nonspecific action (stepping over an object) performed by either a hand or a foot. Hand motor evoked potentials (MEPs) increased for grasping and stepping over actions performed by the hand and for grasping actions performed by the foot. Conversely, foot MEPs increased only for actions performed by the foot. In a second experiment, participants viewed a typical hand action (grasping a pencil) and a typical foot action (pressing a foot-pedal) performed by either a hand or a foot. Again, hand MEPs increased not only during the observation of both actions performed by the hand but also for grasping actions performed by the foot. Foot MEPs increased not only during the observation of grasping and pressing actions performed by the foot but also for pressing actions performed by the hand. This evidence indicates that motor activations by action observation occur also in the muscles typically used to perform the observed action, even when the action is executed by an unusual effector, hence suggesting a double coding of observed actions: a strict somatotopic coding and an action goal coding based on the observer's motor expertise.

Sense of agency in schizophrenia: A reconciliation of conflicting findings through a theory-driven literature review.

The sense of agency is the experience of being the author of self-generated actions and their outcomes. Both clinical manifestations and experimental evidence suggest that the agency experience and the mechanisms underlying agency attribution may be dysfunctional in schizophrenia. Yet, studies investigating the sense of agency in these patients show seemingly conflicting results: some indicated under-attribution of self-agency (coherently with certain positive symptoms), while others suggested over-attribution of self-agency. In this review, we assess whether recent theoretical frameworks can reconcile these divergent results. We examine whether the identification of agency abnormalities in schizophrenia might depend on the measure of self-agency considered (depending on the specific task requirements) and the available agency-related cues. We conclude that all these aspects are relevant to predict and characterize the type of agency misattribution that schizophrenia patients might show. We argue that one particular model, based on the predictive coding theory, can reconcile the interpretation of the multifarious phenomenology of agency manifestations in schizophrenia, paving the way for testing agency disorders in novel ways.

Sensory Attenuation Deficit and Auditory Hallucinations in Schizophrenia: A Causal Mechanism or a Risk Factor? Evidence From Meta-Analyses on the N1 Event-Related Potential Component.

BACKGROUND: Sensory attenuation (SA), the dampened perception of self-generated sensory information, is typically associated with reduced event-related potential signals, such as for the N1 component of auditory event-related potentials. SA, together with efficient monitoring of intentions and actions, should facilitate the distinction between self-generated and externally generated sensory events, thereby optimizing interaction with the world. According to many, SA is deficient in schizophrenia. The question arises whether altered SA reflects a sufficient mechanism to explain positive symptoms such as auditory hallucinations. A systematic association of reduced auditory SA in hallucinating patients would support this hypothesis. METHODS: We conducted a series of meta-analyses on 15 studies on auditory SA in which the N1 component of event-related potential-electroencephalogram signals was measured during talking (self-generated sensory signals condition) or when listening to prerecorded vocalizations (externally generated sensory signals condition). RESULTS: We found that individuals with schizophrenia did show some auditory SA because their N1 signal was significantly attenuated in talking conditions compared with listening conditions. However, the magnitude of such attenuation was reduced in individuals with schizophrenia compared to healthy control participants. This phenomenon generalizes independently from the stage of the disease, the severity of positive symptoms, and whether patients have auditory hallucinations or not. CONCLUSIONS: These findings suggest that reduced SA cannot be a sufficient mechanism for explaining positive symptoms such as auditory hallucinations in schizophrenia. Because reduced SA was also present in participants at risk of schizophrenia, reduced SA may represent a risk factor for the disorder. We discuss the implications of these results for clinical-cognitive models of schizophrenia.

Forearm bisection task suggests an alteration in body schema in patients with functional movement disorders (motor conversion disorders).

OBJECTIVES: To explore potential alterations of the Body Schema, the implicit sensorimotor representation of one's own body, in patients with Functional Movement Disorders (FMD, Motor Conversion Disorders), characterized by neurological symptoms of altered voluntary motor function that cannot be explained by typical medical conditions. This investigation is prompted by the potential dissociation from their reportedly intact sense of ownership. METHODS: 10 FMD patients and 11 healthy controls (HC) underwent the Forearm Bisection Task, aimed at assessing perceived body metrics, which consists in asking the subject, blindfolded, to repeatedly point at the perceived middle point of their dominant forearm with the index finger of their contralateral hand, and a psychometric assessment for anxiety, depression, alexithymia, and tendency to dissociation. RESULTS: FMD patients bisected their forearm more proximally (with an increased shift towards their elbow equal to 7.5%) with respect to HC; average bisection point was positively associated with anxiety levels in the whole sample, and with the tendency to dissociation in the FMD group. CONCLUSIONS: FMD patients perceive their forearm as shorter than HC, suggesting an alteration of their Body Schema. The Body Schema can go through short- and long-term updates in the life course, mainly related to the use of each body segment; we speculate that, despite FMD being a disorder of functional nature, characterized by variability and fluctuations in symptomatology, the lack of sense of agency over a body part might be interpreted by the nervous system as disuse and hence influence the Body Schema, as deficits of organic etiology do.

Touch to see: neuropsychological evidence of a sensory mirror system for touch.

The observation of touch can be grounded in the activation of brain areas underpinning direct tactile experience, namely the somatosensory cortices. What is the behavioral impact of such a mirror sensory activity on visual perception? To address this issue, we investigated the causal interplay between observed and felt touch in right brain-damaged patients, as a function of their underlying damaged visual and/or tactile modalities. Patients and healthy controls underwent a detection task, comprising visual stimuli depicting touches or without a tactile component. Touch and No-touch stimuli were presented in egocentric or allocentric perspectives. Seeing touches, regardless of the viewing perspective, differently affects visual perception depending on which sensory modality is damaged: In patients with a selective visual deficit, but without any tactile defect, the sight of touch improves the visual impairment; this effect is associated with a lesion to the supramarginal gyrus. In patients with a tactile deficit, but intact visual perception, the sight of touch disrupts visual processing, inducing a visual extinction-like phenomenon. This disruptive effect is associated with the damage of the postcentral gyrus. Hence, a damage to the somatosensory system can lead to a dysfunctional visual processing, and an intact somatosensory processing can aid visual perception.

The influence of arm posture on the Uznadze haptic aftereffect.

The role of arm posture in the Uznadze haptic aftereffect is investigated: two identical test stimuli (i.e., spheres, TS) clenched simultaneously appear haptically different in size after hands have been adapted to two spheres (adapting stimuli, AS) differing in size: the hand adapted to a small AS feels TS bigger than the hand adapted to a big AS. In two experiments, participants evaluated the haptic impressions of two TS after adaptation by finding their match on a visual scale. In Experiment 1, all tasks were carried out with arms either uncrossed or crossed. In Experiment 2, only the matching task was performed with arms either uncrossed or crossed while adaptation was conducted by continuously changing arm posture from uncrossed to crossed and vice versa. The illusion occurred irrespectively of arm posture; however, its magnitude was smaller when adaptation was carried out in the classical condition of uncrossed arms. Results are discussed in light of two functional mechanisms: low-level somatotopic mapping (i.e., stimuli conformation) and high-level level factors (i.e., arm posture) that could modulate the haptic perception. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Hearing shapes our perception of time: temporal discrimination of tactile stimuli in deaf people.

Confronted with the loss of one type of sensory input, we compensate using information conveyed by other senses. However, losing one type of sensory information at specific developmental times may lead to deficits across all sensory modalities. We addressed the effect of auditory deprivation on the development of tactile abilities, taking into account changes occurring at the behavioral and cortical level. Congenitally deaf and hearing individuals performed two tactile tasks, the first requiring the discrimination of the temporal duration of touches and the second requiring the discrimination of their spatial length. Compared with hearing individuals, deaf individuals were impaired only in tactile temporal processing. To explore the neural substrate of this difference, we ran a TMS experiment. In deaf individuals, the auditory association cortex was involved in temporal and spatial tactile processing, with the same chronometry as the primary somatosensory cortex. In hearing participants, the involvement of auditory association cortex occurred at a later stage and selectively for temporal discrimination. The different chronometry in the recruitment of the auditory cortex in deaf individuals correlated with the tactile temporal impairment. Thus, early hearing experience seems to be crucial to develop an efficient temporal processing across modalities, suggesting that plasticity does not necessarily result in behavioral compensation.

Visual perception of bodily interactions in the primary somatosensory cortex.

Brain imaging studies in humans have revealed the existence of a visuo-tactile system, which matches observed touch with felt touch. In this system, the primary somatosensory cortex (SI) appears to play a causal role in the visual processing of tactile events. Whether this visuo-tactile mechanism for touch in SI applies to the sight of 'any' touch, or whether it is restricted to the domain of body-related tactile experiences remains unresolved. To address this issue, repetitive transcranial magnetic stimulation (rTMS) was used to determine whether activity in SI is strictly related to the visual processing of human body-part interactions, or is also involved in processing the contact between inanimate objects, or between human body-parts and objects. The results show that rTMS over SI selectively impaired the processing of a contralateral visual stimulus depicting a human body-part being touched by a human agent, while it did not affect the visual perception of contact between objects, or between human body-parts and objects. Correlation analysis shows that this effect was associated with the intensity and embodiment of the observed touched. This result suggests that SI is more suited to represent social touch, contributing to our understanding of the effect of interpersonal tactile interactions between people.

I am the metre: The representation of one's body size affects the perception of tactile distances on the body.

Humans must ground the perception of one's body in a mental representation to move in space and interact with objects. This representation can be temporarily altered artificially. In the full-body illusion (FBI), participants see a virtual (or filmed) body receiving a tactile stimulation. When participants receive touches on their body similarly to the seen one (i.e., homologous location and synchronous timing), they embody the seen alien body. While the subjective embodiment of alien bodies of different sizes has been already manipulated with the FBI, it remains unexplored whether the body-metric perception is impacted too. We first developed a new setup for the FBI using 360° videos to favour the embodiment. The FBI was induced for bodies of three sizes adopting anatomical and non-anatomical viewpoints, and we measured the subjective embodiment. The results suggest that humans can embody normal size or bigger bodies seen from anatomical viewpoints, but not smaller ones. We then investigated if the FBI modulates the body-metric representation. We found that the resized bodies' vision affects the perception of one's body-metric representation, but this was independent of the embodiment, suggesting that the FBI alters the body representation at different levels with a specific impact.

Sense of body ownership and body agency in schizophrenia.

Recent research suggests that embodiment sensations (sense of body ownership and sense of body agency) are altered in schizophrenia. Using a mirror box illusion setup, we tested if the anomalous embodiment experience depends on deficient processing of visuomotor synchrony, disrupted processing of movement mode, or both. The task required participants to press a lever with their index while looking at the image of the experimenter's hand moving on a similar lever. The illusion of embodiment could arise because looking toward the direction of their own hand the participant saw the reflection of the experimenter's hand visually superimposed to his own one through a mirror. During the illusion induction, we systematically varied visuomotor asynchrony (4 delays were imposed on the movement of the experimenter's hand) and the mode of movement (the participant could perform active vs. passive movements). The strength of the illusion of embodiment of the external hand was assessed with explicit judgments of ownership and agency. Patients' data showed an anomalous modulation of ownership with respect to visuomotor synchrony manipulation and an altered modulation of agency with respect to both visuomotor synchrony and movement mode manipulations. Results from the present study suggest that impairments affecting both the processing of temporal aspects of visuomotor signals and the processing of type of movement underlie anomalous embodiment sensations in schizophrenia. Hypotheses about potential deficits accounting for our results are proposed.