The role of self-touch in somatosensory and body representation disorders after stroke

Alterations of tactile and anatomical spatial representations of the hand after stroke

Stroke often causes long-term motor and somatosensory impairments. Motor planning and tactile perception rely on spatial body representations. However, the link between altered spatial body representations, motor deficit and tactile spatial coding remains unclear. This study investigates the relationship between motor deficits and alterations of anatomical (body) and tactile spatial representations of the hand in 20 post-stroke patients with upper limb hemiparesis. Anatomical and tactile spatial representations were assessed from 10 targets (nails and knuckles) respectively cued verbally by their anatomical name or using tactile stimulations. Two distance metrics (hand width and finger length) and two structural measures (relative organization of targets positions and angular deviation of fingers from their physical posture) were computed and compared to clinical assessments, normative data and lesions sites. Over half of the patients had altered anatomical and/or tactile spatial representations. Metrics of tactile and anatomical representations showed common variations, where a wider hand representation was linked to more severe motor deficits. In contrast, alterations in structural measures were not concomitantly observed in tactile and anatomical representations and did not correlate with clinical assessments. Finally, a preliminary analysis showed that specific alterations in tactile structural measures were associated with dorsolateral prefrontal stroke lesions. This study reveals shared and distinct characteristics of anatomical and tactile hand spatial representations, reflecting different mechanisms that can be affected differently after stroke: metrics and location of tactile and anatomical representations were partially shared while the structural measures of tactile and anatomical representations had distinct characteristics.

Active self-touch restores bodily proprioceptive spatial awareness following disruption by 'rubber hand illusion'

Bodily self-awareness relies on a constant integration of visual, tactile, proprioceptive, and motor signals. In the 'rubber hand illusion' (RHI), conflicting visuo-tactile stimuli lead to changes in self-awareness. It remains unclear whether other, somatic signals could compensate for the alterations in self-awareness caused by visual information about the body. Here, we used the RHI in combination with robot-mediated self-touch to systematically investigate the role of tactile, proprioceptive and motor signals in maintaining and restoring bodily self-awareness. Participants moved the handle of a leader robot with their right hand and simultaneously received corresponding tactile feedback on their left hand from a follower robot. This self-touch stimulation was performed either before or after the induction of a classical RHI. Across three experiments, active self-touch delivered after-but not before-the RHI, significantly reduced the proprioceptive drift caused by RHI, supporting a restorative role of active self-touch on bodily self-awareness. The effect was not present during involuntary self-touch. Unimodal control conditions confirmed that both tactile and motor components of self-touch were necessary to restore bodily self-awareness. We hypothesize that active self-touch transiently boosts the precision of proprioceptive representation of the touched body part, thus counteracting the visual capture effects that underlie the RHI.

Self-touch facilitates the recognition of the dis-owned left hand in somatoparaphrenia: a single case study

We investigated whether self-administered tactile stimulation could act as a temporary restorative mechanism for body ownership disorders, both implicitly and explicitly. We tested this hypothesis in a patient with somatoparaphrenia, who displayed increased accuracy in explicitly recognizing their left hand during self-touch. Furthermore, the patient implicitly perceived their hand and the experimenter's hand as more belonging to their own body compared to conditions where vision was the sole sensory input. These findings highlight the importance of self-touch in maintaining a coherent body representation, while also demonstrating the potential dissociation between the recovery of explicit and implicit perceptions of body ownership.

Key constructs of body awareness impairments post-stroke: a scoping review of assessment tools and interventions

PURPOSE

To summarise body awareness assessment tools and interventions relevant for stroke rehabilitation using a framework that categorises key body awareness constructs, disorders and impairments.

MATERIALS AND METHODS

Online electronic databases and trial registries were searched from inception until July 2021, in addition to hand searching reference lists of included studies and reviews. Study selection included any study design where the investigation involved assessing and/or intervening in body awareness following stroke. Data were extracted based on predefined criteria by two independent reviewers and mapped to the emergent framework.

RESULTS

The final analysis included 144 papers that reported 43 assessment tools and 8 types of interventions for body awareness. Consensus was reached on a synthesised body awareness framework. This comprised specific impairments and disorders, constructs, sub-categories and main categories leading to the overarching term of body awareness. Clinical and psychometric properties of the assessment tools were not reported or poorly evaluated, and the interventions lacked robust study designs and rigorous methods.

CONCLUSIONS

The framework produced will enable future research and clinical practice to be based on consistent concepts and definitions. Clinicians can also use this information to cautiously select assessment tools and/or interventions but are reminded of the limitations identified in this review.Implications for rehabilitationThere is limited understanding, compounded by inconsistent terminology and definitions regarding body awareness after stroke.A synthesized framework to define key constructs and definitions of body awareness is proposed.Assessment tools and interventions reported in the literature are mapped to the proposed framework.Psychometric properties of available tools are reported.Significant work remains to refine concepts of body awareness, develop and evaluate assessment tools and interventions.

Touching with the eyes: Oculomotor self-touch induces illusory body ownership

Self-touch plays a central role in the construction and plasticity of the bodily self. But which mechanisms support this role? Previous accounts emphasize the convergence of proprioceptive and tactile signals from the touching and the touched body parts. Here, we hypothesise that proprioceptive information is not necessary for self-touch modulation of body-ownership. Because eye movements do not rely on proprioceptive signals as limb movements do, we developed a novel oculomotor self-touch paradigm where voluntary eye movements generated corresponding tactile sensations. We then compared the effectiveness of eye versus hand self-touch movements in generating an illusion of owning a rubber hand. Voluntary oculomotor self-touch was as effective as hand-driven self-touch, suggesting that proprioception does not contribute to body ownership during self-touch. Self-touch may contribute to a unified sense of bodily self by binding voluntary actions toward our own body with their tactile consequences.

An integrative perspective on the role of touch in the development of intersubjectivity

Touch concerns a fundamental component of sociality. In this review, we examine the hypothesis that somatomotor development constitutes a crucial psychophysiological element in the ontogeny of intersubjectivity. An interdisciplinary perspective is provided on how the communication channel of touch contributes to the sense of self and extends to the social self. During gestation, the transformation of random movements into organized sequences of actions with sensory consequences parallels the development of the brain's functional architecture. Brain subsystems shaped by the coordinated activity of somatomotor circuits to support these first body-environment interactions are the first brain functional arrangements to develop. We propose that tactile self-referring behaviour during gestation constitutes a prototypic mode of interpersonal exchange that supports the subsequent development of intersubjective exchange. The reviewed research suggests that touch constitutes a pivotal bodily experience that in early stages builds and later filters self-other interactions. This view is corroborated by the fact that aberrant social-affective touch experiences appear fundamentally associated with attachment anomalies, interpersonal trauma, and personality disorders. Given the centrality of touch for the development of intersubjectivity and for psychopathological conditions in the social domain, dedicated research is urged to elucidate the role of touch in the evolution of subjective self-other coding.

[To experience one's physicality through the "bizarre" experience of touching oneself]

The touch of oneself is essential in the construction of a conscious self. It contributes to the feeling of ownership of the body. Feeling touched and touching reveals the subject in a being-self inscribed in its environment. This sensory experience can be disturbing for the subject. A study conducted with adolescent girls with obesity has shown that this haptic experience, during a postural session, can generate a feeling of strangeness. This singular discovery of oneself reveals the opening towards new exploratory fields of the body self-consciousness, during our care.

The off-line effect of affective touch on multisensory integration and tactile perceptual accuracy during the somatic signal detection task

Affective touch refers to the emotional and motivational facets of tactile sensation and has been linked to the activation of a specialised system of mechanosensory afferents (the CT system), that respond optimally to slow caress-like touch. Affective touch has been shown to play an important role in the building of the bodily self: the multisensory integrated global awareness of one's own body. Here we investigated the effects of affective touch on subsequent tactile awareness and multisensory integration using the Somatic Signal Detection Task (SSDT). During the SSDT, participants were required to detect near-threshold tactile stimulation on their cheek, in the presence/absence of a concomitant light. Participants repeated the SSDT twice, before and after receiving a touch manipulation. Participants were divided into two groups: one received affective touch (CT optimal; n = 32), and the second received non-affective touch (non-CT optimal; n = 34). Levels of arousal (skin conductance levels, SCLs) and mood changes after the touch manipulation were also measured. Affective touch led to an increase in tactile accuracy, as indicated by less false reports of touch and a trend towards higher tactile sensitivity during the subsequent SSDT. Conversely, non-affective touch was found to induce a partial decrease in the correct detection of touch possibly due to a desensitization of skin mechanoreceptors. Both affective and non-affective touch induced a more positive mood and higher SCLs in participants. The increase in SCLs was greater after affective touch. We conclude that receiving affective touch enhances the sense of bodily self therefore increasing perceptual accuracy and awareness. Higher SCLs are suggested to be a possible mediator linking affective touch to a greater tactile accuracy. Clinical implications are discussed.

Stop touching your face! A systematic review of triggers, characteristics, regulatory functions and neuro-physiology of facial self touch

Spontaneous face touching (sFST) is an ubiquitous behavior that occurs in people of all ages and all sexes, up to 800 times a day. Despite their high frequency, they have rarely been considered as an independent phenomenon. Recently, sFST have sparked scientific interest since they contribute to self-infection with pathogens. This raises questions about trigger mechanisms and functions of sFST and whether they can be prevented. This systematic comprehensive review compiles relevant evidence on these issues. Facial self-touches seem to increase in frequency and duration in socially, emotionally as well as cognitively challenging situations. They have been associated with attention focus, working memory processes and emotion regulating functions as well as the development and maintenance of a sense of self and body. The dominance of face touch over other body parts is discussed in light of the proximity of hand-face cortical representations and the peculiarities of facial innervations. The results show that underlying psychological and neuro-physiological mechanisms of sFST are still poorly understood and that various basic questions remain unanswered.

Staying in touch with our bodies: Stronger sense of ownership during self- compared to other touch despite temporal mismatches

Self-touch is considered important for bodily self-consciousness and self-other distinction and has been reported to improve clinical symptoms of disembodiment. To investigate the link between self-touch and disembodiment in healthy participants, we studied the effect of self-touch versus touch produced by another person (other-touch) on experimentally induced disembodiment. In a mixed reality paradigm, across two experiments, participants could see their own body and surroundings with a controllable visual delay and either stroked their own hand with a paintbrush or were stroked with it by the experimenter. Experiment 1 first assessed the sensitivity to temporal multimodal mismatches and delay-induced changes in the sense of body ownership in three conditions, namely self-touch, other-touch and hidden-self-touch (visually occluding the touching hand). In a second block, we compared phenomenological and physiological (threat response) measures of disembodiment between the self-touch and other-touch conditions. Experiment 2 roughly replicated the first block of Experiment 1 but included a condition in which participants performed the self-touch gesture without touching their hand. Such experiment attempted to control for the potential role of efferent signals. Our results show that increasing visual delay generally enhances the feeling of disembodiment, yet the decrease of body ownership is less pronounced during self-touch. For sensitivity to delay between conditions, however, diverging findings are discussed. This study provides evidence for the importance of self-touch in sustaining a healthy sense of body in the context of disembodiment.

How the unconscious mind controls body movements: Body schema distortion in anorexia nervosa

OBJECTIVE

Besides all visible somatic manifestations, distorted body representation is a key symptom for anorexia nervosa (AN). Body representation can be divided into a conscious component, body image, and an unconscious action-related one, body schema. As behavioral studies already explored the impact of a distorted body image in AN, we aimed to explore whether distortion also extends into unconscious body schema. This study is the first with an unbiased measurement of the body schema in a homogeneous sample of AN patients.

METHOD

Twenty-three patients diagnosed with AN and 23 healthy controls (HC) walked through a door like aperture varying in width. Door width was based on participants shoulder width and ranged from an aperture-to-shoulder-ratio of (A/S) 0.9 to 1.45. Shoulder rotation was measured as indication of perceived body width. To measure the unconscious body schema, we used a cover story pretending to investigate the influence of change of position on retention memory.

RESULTS

We found a significantly higher critical A/S for AN than HC, which indicates that AN patients rotate their shoulders for relatively larger door widths than HC, thus unconsciously estimating their body size to be larger than in reality. Additionally, we found a correlation between negative body attribution and overestimation of bodily dimensions.

DISCUSSION

As stated by the "allocentric-lock"-hypothesis, AN patients might be locked to a stored representation of their body that cannot be updated and remains at pre-AN conditions. We suggest future AN-therapy to counter body schema alterations by combining cognitive behavioral therapy and virtual reality therapy.

Étude qualitative de l’expérience psychocorporelle des autotouchers faciaux spontanés chez des infirmiers portés volontaires en renfort covid

Introduction : The COVID-19 pandemic has warranted the implementation of barrier actions and the wearing of personal protective equipment (PPE). These behavioral adaptations counteract spontaneous self-touching reflex gestures. I propose to explore the mind-body experience generated by these gesture changes in this health context.Method : I conducted a qualitative study with nine nurses who volunteered as reinforcements. The semistructured interviews I carried out were analyzed using the interpretative phenomenological analysis approach.Results : The perception of the risk of self-inoculation is not related to the level of virus exposure. Facial PPE is perceived both as reassuring and difficult to put up with. The experience of self-touches is influenced by the level of attention the subject pays to his or her face and by the medical background related to this. Three kinds of mind-body adaptations are used to control self-touching : control by avoidance, control by keeping one’s hands busy, and compensatory bodily strategies. The representations of the bodily self are modified in terms of gestures and of the feeling of humanness. This generates a form of bodily abandonment and a lived experience of soiled bodies.Conclusion : The results highlight the cognitive load involved in refraining from self-touching and with the wearing of facial PPE. They emphasize the importance of questioning the implications of these sensorimotor modifications. Supporting health professionals in assessing the mind-body repercussions in a pandemic situation appears key.

The Anticipation and Perception of Affective Touch in Women with and Recovered from Anorexia Nervosa

Disruptions in reward processing and anhedonia have long been observed in Anorexia Nervosa (AN). Interoceptive deficits have also been observed in AN, including reduced tactile pleasure. However, the extent to which this tactile anhedonia is specifically liked to an impairment in a specialised, interoceptive C-tactile system originating at the periphery, or a more top-down mechanism in the processing of tactile pleasantness remains debated. Here, we investigated differences between patients with and recovered from AN (RAN) and healthy controls (HC) in the perception of pleasantness of touch delivered in a CT-optimal versus a CT-non-optimal manner, and in their top-down, anticipatory beliefs about the perceived pleasantness of touch. To this end, we measured the anticipated pleasantness of various materials touching the skin and the perceived pleasantness of light, dynamic touch applied to the forearm of 27 women with AN, 24 women who have recovered and 30 HCs using C Tactile (CT) afferents-optimal (slow) and non-optimal (fast) velocities. Our results showed that both clinical groups anticipated tactile experiences and rated delivered tactile stimuli as less pleasant than HCs, but the latter difference was not related to the CT optimality of the stimulation. Instead, differences in the perception of CT-optimal touch were predicted by differences in top-down beliefs, alexithymia and interoceptive sensibility. Thus, tactile anhedonia in AN might persist as a trait even after otherwise successful recovery of AN and it is not linked to a bottom-up interoceptive deficit in the CT system, but rather to a learned, defective top-down anticipation of tactile pleasantness.

Integrating mental imagery and fascial tissue: A conceptualization for research into movement and cognition

Mental imagery (MI) research has mainly focused to date on mechanisms of effect and performance gains associated with muscle and neural tissues. MI's potential to affect fascia has rarely been considered. This paper conceptualizes ways in which MI might mutually interact with fascial tissue to support performance and cognitive functions. Such ways acknowledge, among others, MI's positive effect on proprioception, body schema, and pain. Drawing on cellular, physiological, and functional similarities and associations between muscle and fascial tissues, we propose that MI has the potential to affect and be affected by fascial tissue. We suggest that fascia-targeted MI (fascial mental imagery; FMI) can therefore be a useful approach for scientific as well as clinical purposes. We use the example of fascial dynamic neuro-cognitive imagery (FDNI) as a codified FMI method available for scientific and therapeutic explorations into rehabilitation and prevention of fascia-related disabling conditions.

Non-invasive Brain Stimulation of the Posterior Parietal Cortex Alters Postural Adaptation

Effective central sensory integration of visual, vestibular, and proprioceptive information is required to promote adaptability in response to changes in the environment during postural control. Patients with a lesion in the posterior parietal cortex (PPC) have an impaired ability to form an internal representation of body position, an important factor for postural control and adaptation. Suppression of PPC excitability has also been shown to decrease postural stability in some contexts. As of yet, it is unknown whether stimulation of the PPC may influence postural adaptation. This investigation aimed to identify whether transcranial direct current stimulation (tDCS) of the bilateral PPC could modulate postural adaptation in response to a bipedal incline postural adaptation task. Using young, healthy subjects, we delivered tDCS over bilateral PPC followed by bouts of inclined stance (incline-interventions). Analysis of postural after-effects identified differences between stimulation conditions for maximum lean after-effect (LAE; p = 0.005) as well as a significant interaction between condition and measurement period for the average position (p = 0.03). We identified impaired postural adaptability following both active stimulation conditions. Results reinforce the notion that the PPC is involved in motor adaptation and extend this line of research to the realm of standing posture. The results further highlight the role of the bilateral PPC in utilizing sensory feedback to update one's internal representation of verticality and demonstrates the diffuse regions of the brain that are involved in postural control and adaptation. This information improves our understanding of the role of the cortex in postural control, highlighting the potential for the PPC as a target for sensorimotor rehabilitation.

Multiple Network Disconnection in Anosognosia for Hemiplegia

Anosognosia for hemiplegia (AHP) is a complex syndrome whose neural correlates are still under investigation. One hypothesis, mainly based on lesion mapping studies, is that AHP reflects a breakdown of neural systems of the right hemisphere involved in motor function. However, more recent theories have suggested that AHP may represent a disorder of cognitive systems involved in belief updating, self-referential or body processing. Two recent studies, using a method to estimate the degree of white matter disconnection from lesions, have indeed shown that patients with AHP suffer from damage of several long-range white matter pathways in association cortex. Here, we use a similar indirect disconnection approach to study a group of patients with motor deficits without anosognosia (hemiparesis or hemiplegia, HP, n = 35), or motor deficits with AHP (n = 28). The HP lesions came from a database of stroke patients, while cases of AHP were selected from the published literature. Lesions were traced into an atlas from illustrations of the publications using a standard method. There was no region in the brain that was more damaged in AHP than HP. In terms of structural connectivity, AHP patients had a similar pattern of disconnection of motor pathways to HP patients. However, AHP patients also showed significant disconnection of the right temporo-parietal junction, right insula, right lateral and medial prefrontal cortex. These associative cortical regions were connected through several white matter tracts, including superior longitudinal fasciculus III, arcuate, fronto-insular, frontal inferior longitudinal, and frontal aslant. These tracts connected regions of different cognitive networks: default, ventral attention, and cingulo-opercular. These results were not controlled for clinical variables as concomitant symptoms and other disorders of body representation were not always available for co-variate analysis. In conclusion, we confirm recent studies of disconnection demonstrating that AHP is not limited to dysfunction of motor systems, but involves a much wider set of large-scale cortical networks.

Welcoming back my arm: affective touch increases body ownership following right-hemisphere stroke

Right-hemisphere stroke can impair the ability to recognize one’s contralesional body parts as belonging to one’s self. The study of this so-called ‘disturbed sense of limb ownership’ can provide unique insights into the neurocognitive mechanisms of body ownership. In this study, we address a hypothesis built upon experimental studies on body ownership in healthy volunteers. These studies have shown that affective (pleasant) touch, an interoceptive modality associated with unmyelinated, slow-conducting C-tactile afferents, has a unique role in the sense of body ownership. In this study, we systematically investigated whether affective touch stimulation could increase body ownership in patients with a disturbed sense of limb ownership following right-hemisphere stroke. An initial feasibility study in 16 adult patients with acute stroke enabled us to optimize and calibrate an affective touch protocol to be administered by the bedside. The main experiment, conducted with a different sample of 26 right hemisphere patients, assessed changes in limb ownership elicited following self- (patient) versus other- (experimenter) generated tactile stimulation, using a velocity known to optimally activate C-tactile fibres (i.e. 3 cm/s), and a second velocity that is suboptimal for C-tactile activation (i.e. 18 cm/s). We further examined the specificity and mechanism of observed changes in limb ownership in secondary analyses looking at (i) the influence of perceived intensity and pleasantness of touch, (ii) touch laterality and (iii) level of disturbed sense of limb ownership on ownership change and (iv) changes in unilateral neglect arising from touch. Findings indicated a significant increase in limb ownership following experimenter-administered, C-tactile-optimal touch. Voxel-based lesion-symptom mapping identified damage to the right insula and, more substantially, the right corpus callosum, associated with a failure to increase body ownership following experimenter-administered, affective touch. Our findings suggest that affective touch can increase the sense of body-part ownership following right-hemisphere stroke, potentially due to its unique role in the multisensory integration processes that underlie the sense of body ownership.

Prerequisites for an Artificial Self

Traditionally investigated in philosophy, body ownership and agency-two main components of the minimal self-have recently gained attention from other disciplines, such as brain, cognitive and behavioral sciences, and even robotics and artificial intelligence. In robotics, intuitive human interaction in natural and dynamic environments becomes more and more important, and requires skills such as self-other distinction and an understanding of agency effects. In a previous review article, we investigated studies on mechanisms for the development of motor and cognitive skills in robots (Schillaci et al., 2016). In this review article, we argue that these mechanisms also build the foundation for an understanding of an artificial self. In particular, we look at developmental processes of the minimal self in biological systems, transfer principles of those to the development of an artificial self, and suggest metrics for agency and body ownership in an artificial self.

Enriching footsteps sounds in gait rehabilitation in chronic stroke patients: a pilot study

In the context of neurorehabilitation, sound is being increasingly applied for facilitating sensorimotor learning. In this study, we aimed to test the potential value of auditory stimulation for improving gait in chronic stroke patients by inducing alterations of the frequency spectra of walking sounds via a sound system that selectively amplifies and equalizes the signal in order to produce distorted auditory feedback. Twenty-two patients with lower extremity paresis were exposed to real-time alterations of their footstep sounds while walking. Changes in body perception, emotion, and gait were quantified. Our results suggest that by altering footsteps sounds, several gait parameters can be modified in terms of left-right foot asymmetry. We observed that augmenting low-frequency bands or amplifying the natural walking sounds led to a reduction in the asymmetry index of stance and stride times, whereas it inverted the asymmetry pattern in heel-ground exerted force. By contrast, augmenting high-frequency bands led to opposite results. These gait changes might be related to updating of internal forward models, signaling the need for adjustment of the motor system to reduce the perceived discrepancies between predicted-actual sensory feedbacks. Our findings may have the potential to enhance gait awareness in stroke patients and other clinical conditions, supporting gait rehabilitation.

Where is my mouth? Rapid experience-dependent plasticity of perceived mouth position in humans

Several neural and behavioural studies propose that movements of the hand to the mouth are a key motor primitive of the primate sensorimotor system. These studies largely focus on sensorimotor coordination required to reach the mouth with the hand. However, hand-to-mouth movement depends on representing the location of the mouth. We report 5 experiments using a novel dental model illusion (DMI) that investigates the neural representation of mouth position. When participants used their right index finger to touch the teeth of an unseen dental model in synchrony with the experimenter's tactile stimulation of the participant's own teeth, participants felt that the position of their own teeth was shifted towards the dental model and stated that their right index finger was touching their actual teeth. This result replicated across four experiments and provides an oral analogue to the rubber hand illusion. Synchrony between the two tactile motions was necessary condition to elicit DMI (Experiment 3). DMI was moderately affected by manipulating the macrogeometric or microgeometric tactile properties of the dental model, suggesting cognitive images of one's own oral morphology play a modest role (Experiments 4 and 5). Neuropsychological theories often stress that hand-to-mouth movement emerges early in development or may even be innate. Our research suggests that general, bottom-up principles of multisensory plasticity suffice to provide spatial representation of the egocentric core, including mouth position.

Taxonomising delusions: content or aetiology?

INTRODUCTION

Many theoretical treatments assume (often implicitly) that delusions ought to be taxonomised by the content of aberrant beliefs. A theoretically sound, and comparatively under-explored, alternative would split and combine delusions according to their underlying cognitive aetiology.

METHODS

We give a theoretical review of several cases, focusing on monothematic delusions of misidentification and on somatoparaphrenia.

RESULTS

We show that a purely content-based taxonomy is empirically problematic. It does not allow for projectability of discoveries across all members of delusions so delineated, and lumps together delusions that ought to be separated. We demonstrate that an aetiological approach is defensible, and further that insofar as content-based approaches are plausible, it is only to the extent that they implicitly link content to aetiology.

CONCLUSIONS

We recommend a more explicit focus on cognitive aetiology as the grounds for delusion taxonomy, even when that would undermine traditional content-based boundaries. We also highlight the iterative and complex nature of evidence about aetiologically grounded taxonomies.

Potential relationship of self-injurious behavior to right temporo-parietal lesions

Self-injurious behavior (SIB) is associated with several neurologic and psychiatric syndromes but rarely with focal lesions. Two patients with lesions of the right temporo-parietal junction presented to psychiatric inpatient services with SIB in the absence of notable neurologic deficits or suicidal ideation. Right temporo-parietal lesions may be associated with disturbances of agency and body ownership, both of which may facilitate SIB. Misoplegia, or hatred of a limb, may be associated with SIB and has been reported without hemiplegia with a right temporo-parietal lesion. Further study is warranted to improve our understanding of the mechanisms underlying SIB.

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.

Voluntary self-touch increases body ownership

Experimental manipulations of body ownership have indicated that multisensory integration is central to forming bodily self-representation. Voluntary self-touch is a unique multisensory situation involving corresponding motor, tactile and proprioceptive signals. Yet, even though self-touch is frequent in everyday life, its contribution to the formation of body ownership is not well understood. Here we investigated the role of voluntary self-touch in body ownership using a novel adaptation of the rubber hand illusion (RHI), in which a robotic system and virtual reality allowed participants self-touch of real and virtual hands. In the first experiment, active and passive self-touch were applied in the absence of visual feedback. In the second experiment, we tested the role of visual feedback in this bodily illusion. Finally, in the third experiment, we compared active and passive self-touch to the classical RHI in which the touch is administered by the experimenter. We hypothesized that active self-touch would increase ownership over the virtual hand through the addition of motor signals strengthening the bodily illusion. The results indicated that active self-touch elicited stronger illusory ownership compared to passive self-touch and sensory only stimulation, and show an important role for active self-touch in the formation of bodily self.

Spinopelvic balance and body image perception in Parkinson's disease: analysis of correlation

PURPOSE

The purpose of this study was to describe the association between body image perception and sagittal balance (SB) parameters in Parkinson's Disease (PD) patients.

METHODS

77 consecutive PD patients were included: 44 males, 33 females; 68.9 ± 6.8 years; 5.3 ± 3.8 years from diagnosis (YFD); Hoehn Yahr (HY) 2.0 ± 0.8, Unified Parkinson's Disease rating Score-Motor section (UPDRS-M) 11.8 ± 9.3. Spinopelvic angles and SB were radiographically assessed. Body image perception was assessed through Trunk appearance scale (TAPS) and Stunkard Figure rating scale for BMI. Beck Depression Inventory (BDI) was used to evaluate depressive mood.

RESULTS

We detected 32 (41.5 % of cohort) Parkinson Disease patients with scoliosis ≥15° Cobb. The mean calculated BMI was 27.1 ± 3.9 kg/m(2). According to the Figure Rating Scale, the perceived BMI averaged 27.2 ± 4.5 kg/m(2), while the mean desired BMI was 24.4 ± 2.7 kg/m(2), TAPS scored 3.4 ± 0.9 points, while BDI 12.3 ± 7.9 points. TAPS had a weak negative correlation with the duration of disease (r = -0.25, p < 0.05) and a correlation with H&Y score (r = 0.28, p < 0.05). Sacral Slope was weakly correlated to the calculated BMI (r = -0.24, p < 0.05). SSA and SPA had a negative correlation with the TAPS mean score (respectively, r = -0.36 and -0.24, p < 0.05). BDI presented a weak correlation with TAPS (r = 0.27, p < 0.05) but not with self esteemed BMI values (p > 0.05).

CONCLUSIONS

Spinopelvic parameters and depression had a specific and concurrent influence on trunk deformity perception but not on BMI self-esteem.

Somatosensory pleasure circuit: from skin to brain and back

The skin senses serve a discriminative function, allowing us to manipulate objects and detect touch and temperature, and an affective/emotional function, manifested as itch or pain when the skin is damaged. Two different classes of nerve fibre mediate these dissociable aspects of cutaneous somatosensation: (i) myelinated A-beta and A-delta afferents that provide rapid information about the location and physical characteristics of skin contact; and (ii) unmyelinated, slow-conducting C-fibre afferents that are typically associated with coding the emotional properties of pain and itch. However, recent research has identified a third class of C-fibre afferents that code for the pleasurable properties of touch - c-tactile afferents or CTs. Clinical application of treatments that target pleasant, CT-mediated touch (such as massage therapy) could, in the future, provide a complementary, non-pharmacological means of treating both the physical and psychological aspects of chronic skin conditions such as itch and eczema.

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.

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.

EEG changes caused by spontaneous facial self-touch may represent emotion regulating processes and working memory maintenance

Spontaneous facial self-touch gestures (sFSTG) are performed manifold every day by every human being, primarily in stressful situations. These movements are not usually designed to communicate and are frequently accomplished with little or no awareness. The aim of the present study was to investigate whether sFSTG are associated with specific changes in the electrical brain activity that might indicate an involvement of regulatory emotional processes and working memory. Fourteen subjects performed a delayed memory task of complex haptic stimuli. The stimuli had to be explored and then remembered for a retention interval of 5min. The retention interval was interrupted by unpleasant sounds from The International Affective Digitized Sounds and short sound-free periods. During the experiment a video stream of behavior, 19-channel EEG, and EMG (of forearm muscles) were recorded. Comparisons of the behavioral data and spectral power of different EEG frequency bands (theta, alpha, beta, and gamma) were conducted. An increase of sFSTG during the application of unpleasant sounds was observed. A significant increase of spectral theta and beta power was observed after exploration of the stimuli as well as after sFSTG in centro-parietal electrodes. The spectral theta power extremely decreased just before sFSTG during the retention interval. Contrary to this, no significant changes were detected in any of the frequencies when the spectral power before and after instructed facial self-touch movements (b-iFSTG and a-iFSTG) were compared. The changes of spectral theta power in the intervals before and after sFSTG in centro-parietal electrodes imply that sFSTG are associated with cortical regulatory processes in the domains of working memory and emotions.

A new method for assessing self-touch enhancement of the foot in stroke patients with mobility problems

Patient NG is the first reported case of lower-limb 'self-touch enhancement' following stroke. Mobility problems prevented NG from reaching to touch her foot, thus we used a self-touch rubber-hand paradigm to mimic the conditions of self-administered touch. With vision precluded, NG administered stimulation to a prosthetic limb while the Examiner administered synchronous stimulation to NG's affected left foot. NG detected all stimulation administered with our self-touch paradigm, whereas in the control condition (with NG not involved in administering stimulation), NG had failed to detect one-third of Examiner-administered stimulation. When mobility problems are a barrier to investigating self-touch enhancement, the self-touch paradigm can be used to demonstrate residual tactile sensation following stroke.

Body ownership and attention in the mirror: insights from somatoparaphrenia and the rubber hand illusion

The brain receives and synthesises information about the body from different modalities, coordinates and perspectives, and affords us with a coherent and stable sense of body ownership. We studied this sense in a somatoparaphrenic patient and three control patients, all with unilateral right-hemisphere lesions. We experimentally manipulated the visual perspective (direct- versus mirror-view) and spatial attention (drawn to peripersonal space versus extrapersonal space) in an experiment involving recognising one's own hand. The somatoparaphrenic patient denied limb ownership in all direct view trials, but viewing the hand via a mirror significantly increased ownership. The extent of this increase depended on spatial attention; when attention was drawn to the extrapersonal space (near-the-mirror) the patient showed a near perfect recognition of her arm in the mirror, while when attention was drawn to peripersonal space (near-the-body) the patient recognised her arm in only half the mirror trials. In a supplementary experiment, we used the Rubber Hand Illusion to manipulate the same factors in healthy controls. Ownership of the rubber hand occurred in both direct and mirror view, but shifting attention between peripersonal and extrapersonal space had no effect on rubber-hand ownership. We conclude that the isolation of visual perspectives on the body and the division of attention between two different locations is not sufficient to affect body ownership in healthy individuals and right hemisphere controls. However, in somatoparaphrenia, where first-person body ownership and stimulus-driven attention are impaired by lesions to a right-hemisphere ventral attentional-network, the body can nevertheless be recognised as one's own if perceived in a third-person visual perspective and particularly if top-down, spatial attention is directed away from peripersonal space.

Now You Feel both: Galvanic Vestibular Stimulation Induces Lasting Improvements in the Rehabilitation of Chronic Tactile Extinction

Tactile extinction is frequent, debilitating, and often persistent after brain damage. Currently, there is no treatment available for this disorder. In two previous case studies we showed an influence of galvanic vestibular stimulation (GVS) on tactile extinction. Here, we evaluated in further patients the immediate and lasting effects of GVS on tactile extinction. GVS is known to induce polarity-specific changes in cerebral excitability in the vestibular cortices and adjacent cortical areas. Tactile extinction was examined with the Quality Extinction Test (QET) where subjects have to discriminate six different tactile fabrics in bilateral, double simultaneous stimulations on their dorsum of hands with identical or different tactile fabrics. Twelve patients with stable left-sided tactile extinction after unilateral right-hemisphere lesions were divided into two groups. The GVS group (N = 6) performed the QET under six different experimental conditions (two Baselines, Sham-GVS, left-cathodal/right-anodal GVS, right-cathodal/left-anodal GVS, and a Follow-up test). The second group of patients with left-sided extinction (N = 6) performed the QET six times repetitively, but without receiving GVS (control group). Both right-cathodal/left-anodal as well as left-cathodal/right-anodal GVS (mean: 0.7 mA) improved tactile identification of identical and different stimuli in the experimental group. These results show a generic effect of GVS on tactile extinction, but not in a polarity-specific way. These observed effects persisted at follow-up. Sham-GVS had no significant effect on extinction. In the control group, no significant improvements were seen in the QET after the six measurements of the QET, thus ruling out test repetition effects. In conclusion, GVS improved bodily awareness permanently for the contralesional body side in patients with tactile extinction and thus offers a novel treatment option for these patients.

Active touch sensing

Active sensing systems are purposive and information-seeking sensory systems. Active sensing usually entails sensor movement, but more fundamentally, it involves control of the sensor apparatus, in whatever manner best suits the task, so as to maximize information gain. In animals, active sensing is perhaps most evident in the modality of touch. In this theme issue, we look at active touch across a broad range of species from insects, terrestrial and marine mammals, through to humans. In addition to analysing natural touch, we also consider how engineering is beginning to exploit physical analogues of these biological systems so as to endow robots with rich tactile sensing capabilities. The different contributions show not only the varieties of active touch--antennae, whiskers and fingertips--but also their commonalities. They explore how active touch sensing has evolved in different animal lineages, how it serves to provide rapid and reliable cues for controlling ongoing behaviour, and even how it can disintegrate when our brains begin to fail. They demonstrate that research on active touch offers a means both to understand this essential and primary sensory modality, and to investigate how animals, including man, combine movement with sensing so as to make sense of, and act effectively in, the world.