Body schema and body image as internal representations of the body, and their disorders. An historical review.

Since the early 1900s, the terms body schema and body image denoted the internal representations of the body. Bonnier's (1905, Revue Neurologique, 13, 605) schema is a conscious spatial representation of the size, shape, and position of the body, and of body parts, whose dysfunction brings about aschématia, and hypo-, hyper-, and paraschématia. The two schemata of Head and Holmes (1911, Brain, 34, 102) are an unconscious plastic postural schema, for the maintenance of posture and balance and for the coding of the position of body parts, and a conscious superficial schema, for the localisation of somatosensory stimuli. Pick's (1922, Psychologische Forschung, 1, 303) body schema refers to a structural description of the body, including the position of body parts and their spatial relationships, defective in autotopagnosia. Schilder's (1935, The image and appearance of the human body) body image is a comprehensive construct, covering physiological, evolutional, neurological and neuropsychological, psychiatric and sociological aspects. Lhermitte's (1939, L'image de notre corps) image, based on the views of the abovementioned authors, is defective in bodily neuropsychological disorders. The two terms have been used interchangeably, to denote (hemi-)asomatognosia, anosognosia, autotopagnosia, depersonalisation, personal neglect, phantom and supernumerary limbs, somatoparaphrenia. Their properties have been summarized with general dichotomies: schema for action in space ("where" system), image for perception ("what" system), after primary sensory processing. While schema and image fractionated into multiple representations of aspects of the body, the two terms are still used to refer to some of these representations, and to their disorders.

Preserved tactile distance estimation despite body representation distortions in individuals with fibromyalgia.

Our mental representation of our body depends on integrating various sensory modalities, such as tactile information. In tactile distance estimation (TDE) tasks, participants must estimate the distance between two tactile tips applied to their skin. This measure of tactile perception has been linked to body representation assessments. Studies in individuals with fibromyalgia (FM), a chronic widespread pain syndrome, suggest the presence of body representation distortions and tactile alterations, but TDE has never been examined in this population. Twenty participants with FM and 24 pain-free controls performed a TDE task on three Body regions (upper limb, trunk, lower limb), in which they manually estimated the interstimuli distance on a tablet. TDE error, the absolute difference between the estimation and the interstimuli distance, was not different between the Groups, on any Body region. Drawings of their body as they felt it revealed clear and frequent distortions of body representation in the group with FM, compared to negligible perturbations in controls. This contrast between distorted body drawings and unaltered TDE suggests a preserved integration of tactile information but an altered integration of this information with other sensory modalities to generate a precise and accurate body representation. Future research should investigate the relative contribution of each sensory information and prior knowledge about the body in body representation in individuals with FM to shed light on the observed distortions.

Neural Simulation of Actions for Serpentine Robots.

The neural or mental simulation of actions is a powerful tool for allowing cognitive agents to develop Prospection Capabilities that are crucial for learning and memorizing key aspects of challenging skills. In previous studies, we developed an approach based on the animation of the redundant human body schema, based on the Passive Motion Paradigm (PMP). In this paper, we show that this approach can be easily extended to hyper-redundant serpentine robots as well as to hybrid configurations where the serpentine robot is functionally integrated with a traditional skeletal infrastructure. A simulation model is analyzed in detail, showing that it incorporates spatio-temporal features discovered in the biomechanical studies of biological hydrostats, such as the elephant trunk or octopus tentacles. It is proposed that such a generative internal model could be the basis for a cognitive architecture appropriate for serpentine robots, independent of the underlying design and control technologies. Although robotic hydrostats have received a lot of attention in recent decades, the great majority of research activities have been focused on the actuation/sensorial/material technologies that can support the design of hyper-redundant soft/serpentine robots, as well as the related control methodologies. The cognitive level of analysis has been limited to motion planning, without addressing synergy formation and mental time travel. This is what this paper is focused on.

Multisensory conflict affects body schema and reaching space.

Multisensory integration plays a crucial role in building the sense of body ownership, i.e., the perceptual status of one's body for which the body is perceived as belonging to oneself. Temporal and spatial mismatching of visual and tactile signals coming from one's body can reduce ownership feelings towards the body and its parts, i.e., produce disownership feelings. Here, we investigated whether visuo-tactile conflict also affects the sensorimotor representation of the body in space (i.e., body schema) and the perception of the space around the body in terms of action potentiality (i.e., reaching space). In two experiments, body schema (Experiment 1) and reaching space (Experiment 2) were assessed before and after either synchronous or asynchronous visuo-tactile stimulation. Results showed that the asynchronous condition, provoking multisensory conflict, caused disownership over one's hand and concurrently affected the body schema and the reaching space. These findings indicate that body schema and reaching space could be dynamically shaped by the multisensory regularities that build up the sense of body ownership.

Embodiment of underweight and normal-weight avatars affects bodily self-representations in anorexia nervosa.

Body image distortion (BID) is a crucial aspect of anorexia nervosa (AN), leading to body overestimation, dissatisfaction, and low self-esteem. BID significantly influences the onset, maintenance, and relapse of the pathology. We assessed whether a Full Body Illusion (FBI) using under and normal-weight avatars' bodies affects perceptual body image and body schema estimations in both individuals with anorexia nervosa (AN) and healthy controls (HC). After each embodiment procedure, we asked participants to estimate the width of their hips (Perceptual Body Image Task) and the minimum aperture width of a virtual door necessary to pass through it (Body Schema Task). Additionally, we asked participants to rate the avatars in terms of self-similarity, attractiveness, and implicit disgust (i.e., pleasant/unpleasant body odour). Whereas participants with AN (N = 26) showed changes in body schema estimations after embodying the normal-weight avatar, no changes were found in HC (N = 25), highlighting increased bodily self-plasticity in AN. Notably, individuals with AN rated the normal weight avatar as the most similar to their real body, which was also considered the least attractive and the most repulsive. These ratings correlated with BID severity. Furthermore, at the explicit level, all participants reported feeling thinner than usual after embodying the underweight avatar. Overall, our findings suggest that BID in AN engages multiple sensory channels (from visual to olfactory) and components (from perceptual to affective), offering potential targets for innovative non-invasive treatments aimed at modifying flexible aspects of body representation.

Assessment of body Schema distortions in early-onset schizophrenia.

Distorted body representations play a major role in the onset and maintenance of Schizophrenia. However, these distortions are difficult to assess because explicit assessments can provoke intense fears about the body and require a good insight. We proposed an implicit motor imagery task to a 14-year-old girl with Early-Onset Schizophrenia. The test consisted of presenting different openings varying in width. For each aperture, the young girl has to say if she could pass through without turning her shoulders. A critical aperture is determined as the first aperture for which she considered she could no longer pass, compared to her shoulders' width. The girl perceived herself as 51 % wider than she was, indicating a significant oversized body schema. The implicit assessments of body schema generate less anxiety and does not require a great level of insight; moreover, those are promising tools for early detection of disease in prodromal phases of Schizophrenia and assistance with differential diagnosis.

Impact of subclinical neck pain on eye and hand movements in goal-directed upper limb aiming movements.

Individuals with untreated, mild-to-moderate recurrent neck pain or stiffness (subclinical neck pain (SCNP)) have been shown to have impairments in upper limb proprioception, and altered cerebellar processing. It is probable that aiming trajectories will be impacted since individuals with SCNP cannot rely on accurate proprioceptive feedback or feedforward processing (body schema) for movement planning and execution, due to altered afferent input from the neck. SCNP participants may thus rely more on visual feedback, to accommodate for impaired cerebellar processing. This quasi-experimental study sought to determine whether upper limb kinematics and oculomotor processes were impacted in those with SCNP. 25 SCNP and 25 control participants who were right-hand dominant performed bidirectional aiming movements using two different weighted styli (light or heavy) while wearing an eye-tracking device. Those with SCNP had a greater time to and time after peak velocity, which corresponded with a longer upper limb movement and reaction time, seen as greater constant error, less undershoot in the upwards direction and greater undershoot in the downwards direction compared to controls. SCNP participants also showed a trend towards a quicker ocular reaction and movement time compared to controls, while the movement distance was fairly similar between groups. This study indicates that SCNP alters aiming performances, with greater reliance on visual feedback, likely due to altered proprioceptive input leading to altered cerebellar processing.

Experiencing an Elongated Limb in Virtual Reality Modifies the Tactile Distance Perception of the Corresponding Real Limb.

In measurement, a reference frame is needed to compare the measured object to something already known. This raises the neuroscientific question of which reference frame is used by humans when exploring the environment. Previous studies suggested that, in touch, the body employed as measuring tool also serves as reference frame. Indeed, an artificial modification of the perceived dimensions of the body changes the tactile perception of external object dimensions. However, it is unknown if such a change in tactile perception would occur when the body schema is modified through the illusion of owning a limb altered in size. Therefore, employing a virtual hand illusion paradigm with an elongated forearm of different lengths, we systematically tested the subjective perception of distance between two points [tactile distance perception (TDP) task] on the corresponding real forearm following the illusion. Thus, the TDP task is used as a proxy to gauge changes in the body schema. Embodiment of the virtual arm was found significantly greater after the synchronous visuotactile stimulation condition compared with the asynchronous one, and the forearm elongation significantly increased the TDP. However, we did not find any link between the visuotactile-induced ownership over the elongated arm and TDP variation, suggesting that vision plays the main role in the modification of the body schema. Additionally, significant effect of elongation found on TDP but not on proprioception suggests that these are affected differently by body schema modifications. These findings confirm the body schema malleability and its role as a reference frame in touch.

Virtual social grooming in macaques and its psychophysiological effects.

Allogrooming is a widespread, pervasive activity among non-human primates. Besides its hygienic function, it is thought to be instrumental in maintaining social bonds and establishing hierarchical structures within groups. However, the question arises as to whether the physiological and social benefits derived from social touch stem directly from body stimulation, or whether other mechanisms come into play. We address this question by analyzing an elaborate social behavior that we observed in two adult male macaques. This behavior demonstrates the existence of a persistent motivation to interact through a form of simulated grooming, as the animals were housed in adjacent enclosures separated by a glass panel preventing direct tactile contact. We find that such virtual grooming produces similar physiological sensations and social effects as allogrooming. We suggest that this behavior engages affective and reward brain circuits to the same extent as real social touch, and that this is probably achieved through high level processes similar to those involved in bodily illusions or synaesthetic phenomena previously described in humans. This observation reveals the unsuspected capacity of non-human primates to invent alternative, quasi-symbolic strategies to obtain effects similar to those provided by direct bodily interaction, which are so important for maintaining social bonds.

The impact of weight and negative body image on the body schema in undergraduate women.

BACKGROUND AND OBJECTIVES: Alterations of the sensory-motor body schema question the origins of such distortions. For example, in anorexia nervosa where patients think they are broader than they really are (body image) but act as if it was really the case (body schema). To date, the results of studies about what hinders the updating of the body schema so much (weight, body image) have been contradictory. METHODS: We therefore conducted two studies that aimed to assess the impact of weight and body image problems on body schema in 92 young women without anorexia nervosa. For this purpose, we used a new body schema assessment tool (SKIN) that is sensitive enough to detect fine alterations of body schema in seven different body parts. RESULTS: In Study 1, the thinness or overweight of the young women had a major impact on their tactile perception, especially because the assessed body part was a sensitive area for body dissatisfaction in young women (e.g., belly, thigh). In Study 2, the level of body dissatisfaction of the participants in its attitudinal and perceptual dimension also had a negative impact on their body schema, again in interaction with weight and body part. CONCLUSIONS: These results imply that body dissatisfaction and thinness are predictors of massive body schema distortions. An oversized body schema could maintain various weight-control behaviors, thus risking the development, maintenance, or relapse of an eating disorder.

Motor imagery ability in children and adolescents with cerebral palsy: a systematic review and evidence map.

Background: Cerebral palsy (CP) refers to a group of permanent movement and posture disorders. Motor imagery (MI) therapy is known to provide potential benefits, but data on MI ability in children and adolescents with CP is lacking. Objective: A systematic review was performed to explore MI abilities in children and adolescents with CP compared to typically developed (TD) subjects. Methods: We searched on PubMed, Web of Science (WOS), EBSCO, Google Scholar, and PEDro including observational studies. Methodological quality was assessed with the modified Newcastle-Ottawa Scale and evidence map was created to synthesize the evidence qualitatively and quantitatively. Results: Seven cross-sectional studies were selected, which included 174 patients with CP and 321 TD subjects. Three studies explored explicit MI, two MI-execution synchrony, and four implicit MI domains. Methodological quality ranged from 6 to 8 stars. Moderate evidence supported the absence of differences in vividness between the groups. As there was only limited evidence, establishing a clear direction for the results was not possible, especially for the capacity to generate MI, mental chronometry features, and MI-execution synchrony domains. Moderate evidence supported a lower efficiency in cases for hand recognition, derived from a lower accuracy rate, while reaction time remained similar between the two groups. Moderate evidence indicated that patients with CP and TD controls showed similar features on whole-body recognition. Conclusion: Moderate evidence suggests that patients with CP present a reduced ability in hand recognition, which is not observed for whole-body recognition compared to healthy controls. Severe limitations concerning sample size calculations and validity of assessment tools clearly limits establishing a direction of results, especially for explicit MI and MI-Execution synchrony domains. Further research is needed to address these limitations to enhance our comprehension of MI abilities in children, which is crucial for prescribing suitable MI-based therapies in this child population.

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.

Body ownership and kinaesthetic illusions: Dissociated bodily experiences for distinct levels of body consciousness?

Seeing an embodied humanoid avatar move its arms can induce in the observer the illusion that its own (static) arms are moving accordingly, the kinematic signals emanating from this avatar thus being considered like those from the biological body. Here, we investigated the causal relationship between these kinaesthetic illusions and the illusion of body ownership, manipulated through visuomotor synchronisation. The results of two experiments revealed that the sense of body ownership over an avatar seen from a first-person perspective was intimately linked to visuomotor synchrony. This was not the case for kinaesthetic illusions indicating that when superimposed on the biological body, the avatar is inevitably treated at the sensorimotor level as one's own body, whether consciously considered as such or not. The question of whether these two bodily experiences (body ownership and kinaesthetic illusion) are underpinned by distinct representations, the body image, and the body schema, is discussed.

Alteration of body representation in typical and atypical motor development.

Developmental coordination disorder (DCD) impacts the quality of life and ability to perform coordinated actions in 5% of school-aged children. The quality of body representations of individuals with DCD has been questioned, but never assessed. We hypothesize that children with DCD have imprecise body representations in the sensory and motor domains. Twenty neurotypical children, seventeen children with DCD (8-12 years old) and twenty neurotypical adults (25-45 years old) performed both sensory and motor body representation tasks: a limb identification and a limb movement task. We observed lower accuracy in the sensory task but not in the motor task. In both tasks, we observe a larger amplitude of errors, or synkinesis, in children with DCD than in neurotypical children. In neurotypical children, accuracy was lower than in neurotypical adults in the motor and sensory task, and the amplitude of sensory errors and synkinesis was higher than in neurotypical adults. Using a linear regression model, we showed that sensory accuracy is a good predictor of synkinesis production, and that synkinesis production is a good predictor of sensory accuracy, as can be expected by the perception-action loop. Results support the hypothesis of an imprecision of body representation in DCD. We suggest that this imprecision arises from noise in the body representation used at the level of internal models of action. Future studies may assess whether slower plasticity of body representations, initial imprecision, or both may account for this observation. At the clinical level, prevention strategies targeting body representation in early childhood are strategically important to limit such impairments. RESEARCH HIGHLIGHTS: Body representation is impaired in children with DCD and has a significant cost in terms of the accuracy of sensory identification of body parts and associated movements. Inaccuracies in the body representation measured in perception and in action (error amplitude and synkinesis) are related in both NT children and adults. In typical development, we provide evidence of a strong link between body schema and body image.

The different impact of attention, movement, and sensory information on body metric representation.

A growing body of research investigating the relationship between body representation and tool-use has shown that body representation is highly malleable. The nature of the body representation does not consist only of sensory attributes but also of motor action-oriented qualities, which may modulate the subjective experience of our own body. However, how these multisensory factors and integrations may specifically guide and constrain body reorientation's plasticity has been under-investigated. In this study, we used a forearm bisection task to selectively investigate the contribution of motor, sensory, and attentional aspects in guiding body representation malleability. Results show that the perceived forearm midpoint deviates from the real one. This shift is further modulated by a motor task but not by a sensory task, whereas the attentional task generates more uncertain results. Our findings provide novel insight into the individual role of movement, somatosensation, and attention in modulating body metric representation.

Action does not drive visual biases in peri-tool space.

Observers experience visual biases in the area around handheld tools. These biases may occur when active use leads an observer to incorporate a tool into the body schema. However, the visual salience of a handheld tool may instead create an attentional prioritization that is not reliant on body-based representations. We investigated these competing explanations of near-tool visual biases in two experiments during which participants performed a target detection task. Targets could appear near or far from a tool positioned next to a display. In Experiment 1, participants showed facilitation in detecting targets that appeared near a simple handheld rake tool regardless of whether they first used the rake to retrieve objects, but participants who only viewed the tool without holding it were no faster to detect targets appearing near the rake than targets that appeared on the opposite side of the display. In a second experiment, participants who held a novel magnetic tool again showed a near-tool bias even when they refrained from using the tool. Taken together, these results suggest active use is unnecessary, but visual salience is not sufficient, to introduce visual biases in peri-tool space.

What you feel is not always what you've got. Jean Lhermitte (1877-1959) and the phantom limb phenomenon.

Jean Lhermitte (1877-1959), the French neurologist and psychiatrist, is most often associated with the sign he described in three patients with multiple sclerosis, back in 1927. In 1937, Lhermitte analytically studied a series of 28 amputees experiencing phantom limb sensations further to amputations dating between 1891 and 1934. After having described the main clinical characteristics of this unpublished series, we will detail the ideas advanced by Jean Lhermitte regarding the phenomenon of the phantom limb. Lhermitte will use these observations to develop conceptions of consciousness and the body schema encompassing very modern resonances.

Transcranial Direct Current Stimulation over the Temporoparietal Junction Modulates Posture Control in Unfamiliar Environments.

The temporoparietal junction (TPJ), which integrates visual, somatosensory, and vestibular information to form body schema, is involved in human postural control. We evaluated whether or not the transcranial direct current stimulation (tDCS) of the TPJ can modulate postural control on an unstable surface with eyes closed, during which the updating of body schema is needed to maintain balance. Sixteen healthy subjects participated in this study. The order of the three types of tDCS (anodal, cathodal, and sham) over the right TPJ was counterbalanced across the participants. We evaluated dynamic posture control while the participants were standing on a stable surface with eyes open and an unstable surface with eyes closed. Anodal tDCS enhanced postural control on an unstable surface with eyes closed during and after stimulation, but cathodal tDCS deteriorated postural control during stimulation. Neither anodal nor cathodal tDCS altered postural control while the participants were on a stable surface with eyes open. Anodal tDCS may enhance postural control with non-vision and altered tactile perception by activating the TPJ, which integrates multisensory inputs to update the body schema, whereas cathodal tDCS has the opposite effect. tDCS over the TPJ may facilitate the updating of body schemas to accommodate changes in sensory inputs and help develop novel approaches to prevent falls.

Low frequency oscillations during hand laterality judgment task with and without personal perspectives: a preliminary study.

Sense of personal perspective is crucial for understanding in attentional mechanisms of the perception in "self" or "other's" body. In a hand laterality judgment (HLJ) task, perception of perspective can be assessed by arranging angular orientations and depths of images. A total of 11 healthy, right-handed participants (8 females, mean age: 38.36 years, education: 14 years) were included in the study. The purpose of this study was to investigate behavioural and cortical responses in low-frequency cortical rhythms during a HLJ task. A total of 80-visual hand stimuli were presented through the experiment. Hand visuals were categorized in the way of side (right vs. left) and perspective (1st vs. 3rd personal perspective). Both behavioural outcomes and brain oscillatory characteristics (i.e., frequency and amplitude) of the Electroencephalography were analysed. All reaction time and incorrect answers for 3rd person perspective were higher than the ones for 1st person perspective. Location effect was statistically significant in event-related theta responses confirming the dominant activity of theta frequency in spatial memory tasks on parietal and occipital areas. In addition, we found there were increasing in delta power and phase in hand visuals with 1st person perspective and increasing theta phase in hand visuals with 3rd person perspective (p < 0.05). Accordingly, a clear dissociation in the perception of perspectives in low-frequency bands was revealed. These different cortical strategy in the perception of hand visual with and without perspectives may be interpreted as delta activity may be related in self-body perception, whereas theta activity may be related in allocentric perception.

An Overview of the Body Schema and Body Image: Theoretical Models, Methodological Settings and Pitfalls for Rehabilitation of Persons with Neurological Disorders.

Given the widespread debate on the definition of the terms "Body Schema" and "Body Image", this article presents a broad overview of the studies that have investigated the nature of these types of body representations, especially focusing on the innovative information about these two representations that could be useful for the rehabilitation of patients with different neurological disorders with motor deficits (especially those affecting the upper limbs). In particular, we analyzed (i) the different definitions and explicative models proposed, (ii) the empirical settings used to test them and (iii) the clinical and rehabilitative implications derived from the application of interventions on specific case reports. The growing number of neurological diseases with motor impairment in the general population has required the development of new rehabilitation techniques and a new phenomenological paradigm placing body schema as fundamental and intrinsic parts for action in space. In this narrative review, the focus was placed on evidence from the application of innovative rehabilitation techniques and case reports involving the upper limbs, as body parts particularly involved in finalistic voluntary actions in everyday life, discussing body representations and their functional role.