The Moving Rubber Hand Illusion Reveals that Explicit Sense of Agency for Tapping Movements Is Preserved in Functional Movement Disorders

Unraveling the mechanisms of high-level gait control in functional gait disorders

Functional gait disorders (FGDs) are a disabling subset of Functional Neurological Disorders in which presenting symptoms arise from altered high-level motor control. The dual-task paradigm can be used to investigate mechanisms of high-level gait control. The study aimed to determine the objective measures of gait that best discriminate between individuals with FGDs and healthy controls and the relationship with disease severity and duration. High-level spatiotemporal gait outcomes were analyzed in 87 patients with FGDs (79.3% women, average age 41.9±14.7 years) and 48 healthy controls (60.4% women, average age 41.9±15.7 years) on single and motor, cognitive, and visual-fixation dual tasks. The area under the curve (AUC) from the receiver operator characteristic plot and the dual-task effect (DTE) were calculated for each measure. Dual-task interference on the top single-task gait characteristics was determined by two-way repeated measures ANOVA. Stride time variability and its standard deviation (SD) failed to discriminate between the two groups in single and dual-task conditions (AUC<0.80 for all). Significant group x task interactions were observed for swing time SD and stride time on the cognitive dual tasks (p<0.035 for all). Longer disease duration was associated with poor gait performance and unsteadiness in motor and cognitive DTE (p<0.003) but improvement in stride length and swing time on the visual dual tasks (p<0.041). Our preliminary findings shed light on measures of gait automaticity as a diagnostic and prognostic gait biomarker and underline the importance of early diagnosis and management in individuals with FGDs.

Virtual reality in functional neurological disorder: a theoretical framework and research agenda for use in the real world

Functional neurological disorder (FND) is a common and disabling condition at the intersection of neurology and psychiatry. Despite remarkable progress over recent decades, the mechanisms of FND are still poorly understood and there are limited diagnostic tools and effective treatments. One potentially promising treatment modality for FND is virtual reality (VR), which has been increasingly applied to a broad range of conditions, including neuropsychiatric disorders. FND has unique features, many of which suggest the particular relevance for, and potential efficacy of, VR in both better understanding and managing the disorder. In this review, we describe how VR might be leveraged in the treatment and diagnosis of FND (with a primary focus on motor FND and persistent perceptual-postural dizziness given their prominence in the literature), as well as the elucidation of neurocognitive mechanisms and symptom phenomenology. First, we review what has been published to date on the applications of VR in FND and related neuropsychiatric disorders. We then discuss the hypothesised mechanism(s) underlying FND, focusing on the features that are most relevant to VR applications. Finally, we discuss the potential of VR in (1) advancing mechanistic understanding, focusing specifically on sense of agency, attention and suggestibility, (2) overcoming diagnostic challenges and (3) developing novel treatment modalities. This review aims to develop a theoretical foundation and research agenda for the use of VR in FND that might be applicable or adaptable to other related disorders.

Predictive Processing and the Pathophysiology of Functional Neurological Disorder

The contemporary neuroscience understanding of the brain as an active inference organ supports that our conscious experiences, including sensorimotor perceptions, depend on the integration of probabilistic predictions with incoming sensory input across hierarchically organized levels. As in other systems, these complex processes are prone to error under certain circumstances, which may lead to alterations in their outcomes (i.e., variations in sensations and movements). Such variations are an important aspect of functional neurological disorder, a complex disorder at the interface of brain-mind-body interactions. Thus, predictive processing frameworks offer fundamental mechanistic insights into the pathophysiology of functional neurological disorder. In recent years, many of the aspects relevant to the neurobiology of functional neurological disorder - e.g., aberrant motor and sensory processes, symptom expectation, self-agency, and illness beliefs, as well as interoception, allostasis, and emotion - have been investigated through the lens of predictive processing frameworks. Here, we provide an overview of the current state of research on predictive processing and the pathophysiology of functional neurological disorder.

How Does Postural Control in Patients with Functional Motor Disorders Adapt to Multitasking-Based Immersive Virtual Reality?

BACKGROUND

Motor symptoms in functional motor disorders (FMDs) refer to involuntary, but learned, altered movement patterns associated with aberrant self-focus, sense of agency, and belief/expectations. These conditions commonly lead to impaired posture control, raising the likelihood of falls and disability. Utilizing visual and cognitive tasks to manipulate attentional focus, virtual reality (VR) integrated with posturography is a promising tool for exploring postural control disorders.

OBJECTIVES

To investigate whether postural control can be adapted by manipulating attentional focus in a 3D immersive VR environment.

METHODS

We compared postural parameters in 17 FMDs patients and 19 age-matched healthy controls over a single session under four increasingly more complex and attention-demanding conditions: simple fixation task (1) in the real room and (2) in 3D VR room-like condition; complex fixation task in a 3D VR city-like condition (3) avoiding distractors and (4) counting them. Dual-task effect (DTE) measured the relative change in performance induced by the different attention-demanding conditions on postural parameters.

RESULTS

Patients reduced sway area and mediolateral center of pressure displacement velocity DTE compared to controls (all, P < 0.049), but only under condition 4. They also showed a significant reduction in the sway area DTE under condition 4 compared to condition 3 (P = 0.025).

CONCLUSIONS

This study provides novel preliminary evidence for the value of a 3D immersive VR environment combined with different attention-demanding conditions in adapting postural control in patients with FMDs. As supported by quantitative and objective posturographic measures, our findings may inform interventions to explore FMDs pathophysiology.

Wearable devices for gait and posture monitoring via telemedicine in people with movement disorders and multiple sclerosis: a systematic review

INTRODUCTION

Wearable devices and telemedicine are increasingly used to track health-related parameters across patient populations. Since gait and postural control deficits contribute to mobility deficits in persons with movement disorders and multiple sclerosis, we thought it interesting to evaluate devices in telemedicine for gait and posture monitoring in such patients.

METHODS

For this systematic review, we searched the electronic databases MEDLINE (PubMed), SCOPUS, Cochrane Library, and SPORTDiscus. Of the 452 records retrieved, 12 met the inclusion/exclusion criteria. Data about (1) study characteristics and clinical aspects, (2) technical, and (3) telemonitoring and teleconsulting were retrieved, The studies were quality assessed.

RESULTS

All studies involved patients with Parkinson's disease; most used triaxial accelerometers for general assessment (n = 4), assessment of motor fluctuation (n = 3), falls (n = 2), and turning (n = 3). Sensor placement and count varied widely across studies. Nine used lab-validated algorithms for data analysis. Only one discussed synchronous patient feedback and asynchronous teleconsultation.

CONCLUSIONS

Wearable devices enable real-world patient monitoring and suggest biomarkers for symptoms and behaviors related to underlying gait disorders. thus enriching clinical assessment and personalized treatment plans. As digital healthcare evolves, further research is needed to enhance device accuracy, assess user acceptability, and integrate these tools into telemedicine infrastructure.

PROSPERO REGISTRATION

CRD42022355460.

Impaired Metacognition of Voluntary Movement in Functional Movement Disorder

BACKGROUND

Motor symptoms in functional movement disorders (FMDs) are experienced as involuntary but share characteristics of voluntary action. Clinical and experimental evidence indicate alterations in monitoring, control, and subjective experience of self-performed movements.

OBJECTIVE

The objective of this study was to test the prediction that FMDs are associated with a reduced ability to make accurate (metacognitive) judgments about self-performed movements.

METHODS

We compared 24 patients with FMD (including functional gait disturbance, functional tremor, and functional tics) with 24 age- and sex-matched healthy control subjects in a novel visuomotor-metacognitive paradigm. Participants performed target-directed movements on a graphics tablet with restricted visual feedback, decided which of two visually presented trajectories was closer to their preceding movement, and reported their confidence in the visuomotor decision. We quantified individual metacognitive performance as participants' ability to assign high confidence preferentially to correct visuomotor decisions.

RESULTS

Patients and control subjects showed comparable motor performance, response accuracy, and use of the confidence scale. However, visuomotor sensitivity in the trajectory judgment was reduced in patients with FMD compared with healthy control subjects. Moreover, metacognitive performance was impaired in patients, that is, their confidence ratings were less predictive of the correctness of visuomotor decisions. Exploratory subgroup analyses suggest metacognitive deficits to be most pronounced in patients with a functional gait disturbance or functional tremor.

CONCLUSIONS

Patients with FMD exhibited deficits both when making visuomotor decisions about their own movements and in the metacognitive evaluation of these decisions. Reduced metacognitive insight into voluntary motor control may play a role in FMD pathophysiology and could lay the groundwork for new treatment strategies. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Improvement in motor symptoms, physical fatigue, and self-rated change perception in functional motor disorders: a prospective cohort study of a 12-week telemedicine program

BACKGROUND

Functional motor disorders (FMDs) are highly disabling conditions associated with long-term disability, poor quality of life, and economic burden on health and social care. While multidisciplinary 5-days rehabilitation programs have been shown to reduce motor and non-motor symptoms, long-term management and monitoring in FMDs remain an unmet need.

AIM

To compare a 12-weeks telemedicine program against a 12-weeks self-management program after a 5-days rehabilitation program for improving motor, non-motor symptoms, quality of life, and perception of change in patients with FMDs.

METHODS

The study population was 64 consecutive patients with a definite diagnosis of FMDs who underwent a 5-days in-person rehabilitation program followed by either a self-management (the first 32 patients) or a telemedicine program (the latter 32 patients). Validated measures of motor and non-motor symptoms such as fatigue and pain, quality of life, perception of change, gait, and postural control were recorded before (T0), after completion of rehabilitation (T1), and then again at 3 months (T2).

RESULTS

Improvement at 3-month follow-up assessment of motor symptoms (p < 0.001), physical fatigue (p = 0.028), and self-rated change perception (p = 0.043) was greater in the telemedicine group. No different between-groups effect was found on other dimensions of fatigue, pain, physical and mental health, and gait and postural control.

CONCLUSIONS

Long-term management and expert monitoring of patients with FMDs via telemedicine may enhance long-term outcomes in motor symptoms and physical fatigue, with a positive long-term impact on self-rated health perception of change.

Economic Costs of Delayed Diagnosis of Functional Motor Disorders: Preliminary Results From a Cohort of Patients of a Specialized Clinic

Background: Functional motor disorders (FMDs) are prevalent and highly disabling conditions in young adults that can result in reduced independence. Despite advances in diagnosis and treatment, the economic burden of FMDs is largely unknown.

Objective: This pilot retrospective study provides a real-world overview of the economic costs related to delayed diagnosis of FMDs from a cohort of patients of a specialized clinic in Italy, based on Italian healthcare costs.

Methods: Sociodemographic data, clinical history, healthcare service utilization, and associated direct costs were collected for a period of up to 5 years before a definite diagnosis of FMDs in 40 patients.

Results: The mean time lag between the onset of FMDs symptoms and diagnosis was 6.63 years (±8.57). The mean annual use of recourses per patient was three specialist visits (95% CI 2.4–3.4) and three diagnostic examinations (95% CI 2.2–3.6) that made up a total of six investigations and over seven (95% CI 5.5–9.7) rehabilitation contacts per year per patient were used before a diagnosis of FMDs was established. In more than 50% of the cases, patients had been hospitalized or made an ER visit at least once before receiving the correct diagnosis. The average annual costs for delayed diagnosis, taking into account only direct healthcare costs (without medications), was about €2,302 (CI 95% €1,570–2,830) per patient [€1,524 covered by the NHS (CI 95% €1,214–1,834) and € 778 by the patient (CI 95% €606–960)]. Hospitalization accounted for €916 (CI 95% €670–1,160) per patient per year, followed by rehabilitation €493 (CI 95% €345–641) and diagnostic tests € 387 (CI 95% €314–460).

Conclusion: These preliminary results shed some light on the high healthcare services volume and direct healthcare costs from clinic to clinic for visits, unnecessary tests, and prescribed treatments in a real-world overview from a cohort of patients of a specialized clinic in Italy. It may represent a starting point for future studies to statistically test and quantify cost reduction after implementing appropriate healthcare pathways.

Sense of agency disturbances in movement disorders: A comprehensive review

Sense of agency refers to the experience that one's self-generated action causes an event in the external environment. Here, we review the behavioural and brain evidence of aberrant experiences of agency in movement disorders, clinical conditions characterized by either a paucity or an excess of movements unrelated to the patient's intention. We show that specific abnormal agency experiences characterize several movement disorders. Those manifestations are typically associated with structural and functional brain abnormalities. However, the evidence is sometimes conflicting, especially when considering results obtained through different agency measures. The present review aims to create order in the existing literature on sense of agency investigations in movement disorders and to provide a coherent overview framed within current neurocognitive models of motor awareness.

Motor dual task with eyes closed improves postural control in patients with functional motor disorders: A posturographic study

BACKGROUND

Functional motor disorders (FMD) are highly disabling neurological conditions in which postural control deficits increase the risk of falls and disability in performing daily living activities. Scattered evidence suggests that such disturbances may depend on abnormal attentional focus and might improve with distraction.

RESEARCH QUESTION

How do motor and cognitive dual tasks performed under two different sensory conditions shape postural control in patients with FMD.

METHODS

This posturographic study involved 30 patients with FMD (age, 45.20 ± 14.57 years) and 30 healthy controls (age, 41.20 ± 16.50 years). Postural parameters were measured with eyes open, and eyes closed in quiet stance (single task) and on a motor dual task (m-DT) and a calculation (cognitive) dual task (c-DT). The dual task effect (DTE, expressed in percentage) on motor and cognitive performance was calculated for sway area, length of Center of Pressure (CoP), and velocity of CoP displacement.

RESULTS

There was a statistically significant three-way interaction between task, condition, and group for the DTE on sway area (p = 0.03). The mean sway area DTE on the motor task in the eyes-closed condition was increased by 70.4 % in the healthy controls, while it was decreased by 1% in the patient group (p = 0.003). No significant three-way interaction was observed for the DTE on length of CoP and velocity of CoP displacement.

SIGNIFICANCE

This study provides novel preliminary evidence for the benefit of a simple motor dual task in the eyes closed condition as a way to improve postural control in patients with FMD. These findings are relevant for the management of postural control disorders in patients with FMD.

Motor and non-motor outcomes after a rehabilitation program for patients with Functional Motor Disorders: A prospective, observational cohort study

BACKGROUND

Rehabilitation has proven effective in improving motor symptoms (i.e., weakness, tremor, gait and balance disorders) in patients with Functional Motor Disorders (FMDs). Its effects on non-motor symptoms (NMSs) such as fatigue, pain, depression, anxiety and alexithymia, have not been explored yet.

OBJECTIVE

To explore the effects of a validated inpatient 5-day rehabilitation program, followed by a home-based self-management plan on functional motor symptoms, NMSs, self-rated perception of change, and quality of life (QoL).

METHODS

33 FMD patients were enrolled. Measures for motor symptoms and NMSs were primary outcomes. Secondary outcomes included measures of self-perception of change and QoL. Patients were evaluated pre-treatment (T0), post-treatment (T1), and 3-month follow-up (T2).

RESULTS

There was an overall significant decrease in functional motor symptoms, general, physical, and reduced-activity fatigue (for all, p < 0.001). Post hoc comparison showed significant improvements at T1, whereas effects remained significant at T2 for motor symptoms and physical fatigue. Gait and balance, alexithymia, and physical functioning (QoL) significantly improved at T2. More than 50% of patients reported marked improvement at T1 and T2.

CONCLUSIONS

Our study suggests the benefits of rehabilitation and self-management plan on functional motor symptoms and physical fatigue in the medium-term. More actions are needed for the management of pain and other distressing NMSs in FMDs.

Bodily self-perception during voluntary actions: The causal contribution of premotor cortex and cerebellum

Voluntary actions are accompanied by the experience of controlling one's own movements (sense of agency) and the feeling that the moving body part belongs to one's self (sense of body ownership). So far, agency and body ownership have been investigated separately, leaving the neural underpinnings of the relation between the two largely unexplored. The aim of this study was to explore the causal role of two multisensory brain regions, that is the premotor cortex (PMc) and the cerebellum, in agency and body ownership concurrently on the same behavioral task, i.e., the moving Rubber Hand Illusion (mRHI). Participants watched a rubber hand while moving their hidden hand. The type of movement (active or passive) and posture of the rubber hand (congruent or incongruent) differed in three conditions (active congruent, passive congruent, active incongruent), so that agency and ownership could be elicited either separately or concurrently. Agency and ownership were measured by subjective report and proprioceptive drift. Sham and anodal transcranial direct current stimulation (tDCS) were delivered to the PMc (Experiment 1) or the cerebellum (Experiment 2) prior to the mRHI task. Independent of the site or type of tDCS, subjective reports revealed that both agency and ownership were evoked in the active congruent condition, ownership but not agency in the passive congruent condition, and agency but not ownership in the active incongruent condition. The proprioceptive drift was evoked in the active congruent and the passive congruent condition. Anodal tDCS over the PMc reduced the feeling of agency in the active congruent condition, while it enhanced proprioceptive drift when applied over the cerebellum. These findings suggest a specific causal contribution of the PMc and the cerebellum to bodily self-perception during voluntary movement, with the PMc mainly involved in awareness of action and the cerebellum in proprioceptive adaptation of body position in space.

Development of a Guidance System for Motor Imagery Enhancement Using the Virtual Hand Illusion

Motor imagery (MI) is widely used to produce input signals for brain-computer interfaces (BCI) due to the similarities between MI-BCI and the planning-execution cycle. Despite its usefulness, MI tasks can be ambiguous to users and MI produces weaker cortical signals than motor execution. Existing MI guidance systems, which have been reported to provide visual guidance for MI and enhance MI, still have limitations: insufficient immersion for MI or poor expandability to MI for another body parts. We propose a guidance system for MI enhancement that can immerse users in MI and will be easy to extend to other body parts and target motions with few physical constraints. To make easily extendable MI guidance system, the virtual hand illusion is applied to the MI guidance system with a motion tracking sensor. MI enhancement was evaluated in 11 healthy people by comparison with another guidance system and conventional motor commands for BCI. The results showed that the proposed MI guidance system produced an amplified cortical signal compared to pure MI (p < 0.017), and a similar cortical signal as those produced by both actual execution (p > 0.534) and an MI guidance system with the rubber hand illusion (p > 0.722) in the contralateral region. Therefore, we believe that the proposed MI guidance system with the virtual hand illusion is a viable alternative to existing MI guidance systems in various applications with MI-BCI.

Self-Body Recognition through a Mirror: Easing Spatial-Consistency Requirements for Rubber Hand Illusion

Considering that humans recognize mirror images as copies of the real world despite misinterpreting optical reflections, spatial disagreement may be accepted in rubber hand illusion (RHI) settings when a mirror is used to show a fake hand. The present study performed two experiments to reveal how self-body recognition of a fake hand via a mirror affects RHI. First, we tested whether illusory ownership of a fake hand seen in a mirror could be induced in our experimental environment (screening experiment). Subjective evaluations using an RHI questionnaire demonstrated that embodiment of the rubber hand was evoked in the presence or absence of a mirror. We then examined whether using a mirror image for RHI allows disagreement in orientation (45 ∘ ) between the rubber and actual hands (main experiment). The participants experienced RHI even when the actual and rubber hands were incongruent in terms of orientation. These findings suggest that using a mirror masks subtle spatial incongruency or degrades the contribution of visual cues for spatial recognition and facilitates multisensory integration for bodily illusions.

Mechanotactile Sensory Feedback Improves Embodiment of a Prosthetic Hand During Active Use

There have been several advancements in the field of myoelectric prostheses to improve dexterity and restore hand grasp patterns for persons with upper limb loss, including robust control strategies, novel sensory feedback, and multifunction prosthetic terminal devices. Although these advancements have shown to improve prosthesis performance, a key element that may further improve acceptance is often overlooked. Embodiment, which encompasses the feeling of owning, controlling and locating the device without the need to constantly look at it, has been shown to be affected by sensory feedback. However, the specific aspects of embodiment that are influenced are not clearly understood, particularly when a prosthesis is actively controlled. In this work, we used a sensorized simulated prosthesis in able-bodied participants to investigate the contribution of sensory feedback, active motor control, and the combination of both to the components of embodiment; using a common methodology in the literature, namely the rubber hand illusion (RHI). Our results indicate that (1) the sensorized simulated prosthesis may be embodied by able-bodied users in a similar fashion as prosthetic devices embodied by persons with upper limb amputation, and (2) mechanotactile sensory feedback might not only be useful for improving certain aspects of embodiment, i.e., ownership and location, but also may have a modulating effect on other aspects, namely sense of agency, when provided asynchronously during active motor control tasks. This work may allow us to further investigate and manipulate factors contributing to the complex phenomenon of embodiment in relation to active motor control of a device, enabling future study of more precise quantitative measures of embodiment that do not rely as much on subjective perception.

Agency judgments in post-stroke patients with sensorimotor deficits

Sense of agency refers to the feeling of being in control of one's actions. Previous research has demonstrated that sense of agency is produced through the sensorimotor system, which is involved in comparing internal predictions with sensory feedback in motor control. Therefore, sensorimotor deficits might impair agency through a sensorimotor system malfunction. The present study examined this hypothesis by investigating post-stroke patients who had suffered a subcortical stroke that damaged regions associated with sensorimotor function. To examine agency judgments with respect to motor control, we adopted a self-other attribution task and applied it to post-stroke patients. Participants traced a horizontal straight line and received visual feedback through a cursor on a monitor. The cursor movement reflected either the participants' actual movement or the movement of an "other" that had been previously recorded. Participants judged whether the cursor movement reflected their own movement (self) or an other's movement while they engaged in four cycles of the horizontal tracing movement. After each trial, participants reported their self-other judgment on a nine-point scale. Post-stroke patients completed the experiment with their paretic as well as their non-paralyzed upper limbs. Compared to healthy controls, patients made significantly more self-attributions of others' movements. Interestingly, such misattributions were observed in the patients' performance using both paretic and non-paralyzed upper limbs. These results suggest that post-stroke patients with sensorimotor deficits form misattributions that cannot be explained solely by the sensorimotor system's role in motor control. We discuss these misattributions in post-stroke patients in terms of cue integration theory.

Effects of Human Synchronous Hand Movements in Eliciting a Sense of Agency and Ownership

The self is built as an entity independent from the external world using the human ability to experience the senses of agency and ownership. Humans usually experience these senses during movement. Nevertheless, researchers recently reported that another person’s synchronous mirror-symmetrical movements elicited both agency and ownership in research participants. However, it is unclear whether this elicitation was caused by the synchronicity or the mirror symmetry of the movements. To address this question, we investigated the effect of interpersonal synchronization on the self-reported sense of agency and ownership in two conditions, using movements with and without mirror symmetry. Participants performed rhythmic hand movements while viewing the experimenter’s synchronous or random hand movements, and then reported their perceptions of agency and ownership in a questionnaire. We observed that agency and ownership were significantly elicited by the experimenter’s synchronous hand movements in both conditions. The results suggested that the synchronous movements of another person—rather than mirror- or non-mirror-symmetrical movements—appear to elicit the experience of a sense of agency and ownership. The results also suggested that people could experience these senses not only from their own movements but also from another person’s synchronous movements.

The Embodiment of Objects: Review, Analysis, and Future Directions

Here we offer a thorough review of the empirical literature on the conditions under which an object, such as a tool or a prosthetic (whether real or virtual), can be experienced as being in some sense a part or extension of one's body. We discuss this literature both from the standpoint of the apparent malleability of our body representations, and also from within the framework of radical embodied cognition, which understands the phenomenon to result not from an alteration to a representation, but rather from the achievement of a certain kind of sensory/motor coupling. We highlight both the tensions between these frameworks, and also areas where they can productively complement one another for future research.

Investigating the Components of Body Image Disturbance Within Eating Disorders

Body image disturbance has been highlighted as a common characteristic within the development and maintenance of clinical eating disorders (EDs), represented by alterations in an individual's bodily experience. However, whilst the perceptual stability of the sense of body ownership has been investigated in ED patients, the stability of the sense of body agency in those with ED is yet to be examined. Therefore, body ownership and body agency were investigated using the moving rubber hand illusion, alongside measures of explicit and implicit body satisfaction. Furthermore, with evidence demonstrating a direct link between perceptual and cognitive-affective components of body image in the healthy population, the relationship between measures of body perception and body satisfaction was investigated. Results showed that both ED and healthy individuals displayed a similar subjective experience of illusory ownership and agency towards the fake hand, following voluntary movement. However, whilst both groups initially overestimated their own hand width prior to the illusion, the ED group displayed a significant reduction in hand size estimation following the illusion, which was not matched to the same degree in healthy individuals. In addition, ED individuals displayed a significantly lower body satisfaction compared with healthy females, on both an explicit and implicit level. Such implicit outcomes were shown to be driven specifically by a weaker association between the self and attractiveness. Finally, a significant relationship was observed between specific perceptual measures and implicit body satisfaction, which highlights the important link between perceptual and cognitive-affective components of one's body image. Together, such findings provide a useful foundation for further research to study the conditions in which these two components relate with regard to body image and its disturbance, particularly in relation to the prognosis and treatment of EDs.

The relationship and difference between delay detection ability and judgment of sense of agency

Judgment of agency involves the comparison of motor intention and proprioceptive/visual feedback, in addition to a range of cognitive factors. However, few studies have experimentally examined the differences or correlations between delay detection ability and judgment of agency. Thus, the present study investigated the relationship between delay detection ability and agency judgment using the delay detection task and the agency attribution task. Fifty-eight participants performed the delay detection and agency attribution tasks, and the time windows of each measure were analyzed using logistic curve fitting. The results revealed that the time window of judgment of agency was significantly longer than that of delay detection, and there was a slight correlation between the time windows in each task. The results supported a two-step model of agency, suggesting that judgment of agency involved not only comparison of multisensory information but also several cognitive factors. The study firstly revealed the model in psychophysical experiments.

Functional Movement Disorders and Placebo: A Brief Review of the Placebo Effect in Movement Disorders and Ethical Considerations for Placebo Therapy

Background

Functional movement disorders are common and disabling neurologic conditions. Patients with functional neurologic disorders represent a large proportion of neurology clinic referrals, and limited availability of subspecialty care creates a considerable burden for the healthcare system. These conditions are currently treated with a combination of physical therapy and cognitive behavioral therapy, with variable success.

Methods

We searched the Medline database for studies on the epidemiology and physiology of functional movement disorders, as well as those on the placebo effect in movement disorders. We reviewed and summarized the literature on these topics and explored ethical issues concerning the administration of placebos to patients with functional movement disorders.

Results

Studies of placebos, particularly in patients with movement disorders, have shown that these "inert" agents can provide demonstrable neurophysiologic benefits, even in open-label studies. Physician surveys have shown that many administer placebos for diagnostic and therapeutic purposes, although there are ethical concerns about this practice. We used a principle-based approach and reviewed ethical arguments for (justice and beneficence) and against (non-maleficence and autonomy) the use of placebos in functional movement disorders. In this context, we argue for the importance of the therapeutic alliance in preserving patient autonomy while exploring the potential benefits of placebo therapy.

Conclusions

An ethical argument is presented in support of nondeceptive clinical placebo use for the treatment of functional movement disorders. Patient and clinician attitudes regarding the use of placebos should be investigated before placebo-therapy trials are conducted.

Metacognition of visuomotor decisions in conversion disorder

Motor conversion disorder (CD) entails genuine disturbances in the subjective experience of patients who maintain they are unable to perform a motor function, despite lack of apparent neurological damage. Abilities by which individuals assess their own capacities during performance in a task are called metacognitive, and distinctive impairment of such abilities is observed in several disorders of self-awareness such as blindsight and anosognosia. In CD, previous research has focused on the recruitment of motor and emotional brain systems, generally linking symptoms to altered limbic-motor interactions; however, metacognitive function has not been studied to our knowledge. Here we tested ten CD patients and ten age-gender matched controls during a visually-guided motor paradigm, previously employed in healthy controls (HC), allowing us to probe for motor awareness and metacognition. Participants had to draw straight trajectories towards a visual target while, unbeknownst to them, deviations were occasionally introduced in the reaching trajectory seen on the screen. Participants then reported both awareness of deviations and confidence in their response. Activity in premotor and cingulate cortex distinguished between conscious and unconscious movement corrections in controls better than patients. Critically, whereas controls engaged the left superior precuneus and middle temporal region during confidence judgments, CD patients recruited bilateral parahippocampal and amygdalo-hippocampal regions instead. These results reveal that distinct brain regions subserve metacognitive monitoring for HC and CD, pointing to different mechanisms and sources of information used to monitor and form confidence judgments of motor performance. While brain systems involved in sensory-motor integration and vision are more engaged in controls, CD patients may preferentially rely on memory and contextual associative processing, possibly accounting for how affect and memories can imbue current motor experience in these patients.

Introduction to the Special Issue on Individual Differences in Multisensory Perception: an Overview

The world is full of objects that can be perceived through multiple different senses to create an integrated understanding of our environment. Since each of us has different biological and psychological characteristics, different people may perceive the world in quite different ways. However, the questions of how and why our multisensory perceptions differ have not been explored in any great depth. This special issue, arising from a series of British Psychological Society-funded seminars, presents new research and opinions on the impacts of a variety of individual differences on multisensory perception. We hope that readers will enjoy this collection of eight papers on individual differences in multisensory perception arising from developmental changes, autism, Down syndrome, migraine, sensory loss and substitution, and personality.