Non-Linear Measures of Postural Control in Response to Painful and Non-Painful Visual Stimuli.

Over the past decade, researchers have focused on studying the functional context of perceiving painful stimuli, particularly concerning the posturographic correlates of emotional processing. The aim of this study was to investigate the differential modulation of non-linear measures characterizing postural control in the context of perceiving painful stimuli. The study involved 36 healthy young participants who, while standing, viewed images depicting feet and hands in painful or non-painful situations, both actively (by imagining themselves affected by the situation) and passively. For Center of Pressure (COP) displacement, three non-linear measures (Sample Entropy, Fractal Dimension, and Lyapunov exponent) were calculated. The results suggest lower values of FD and LyE in response to active stimulation compared to those recorded for passive stimulation. Above all, our results pledge for the usefulness of the Lyapunov exponent for assessing postural modulation dynamics in response to painful stimuli perception. The feasibility of this calculation could provide an interesting insight in the collection of biomarkers related to postural correlates of emotional processes and their modulation in neurological disease where socio-affective functions can be often impaired before cognitive ones.

Posturography Approaches: An Insightful Window to Explore the Role of the Brain in Socio-Affective Processes.

A significant amount of research has highlighted the importance of a motor component in the brain's processing of emotional, motivational and social information. Posturography has emerged as an interesting way to assess motor correlates associated with this process. In this review, we highlight recent results within the functional context of painful stimulus perception and discuss the interest in broadening the use of posturography to other motivational and societal functional contexts. Although characterized by significant feasibility, the single measurement of the COP's anteroposterior displacement presents limitations for attesting approach-avoidance behavior towards a visual target. Here, we discuss a number of methodological avenues that could go some way towards overcoming these limitations.

Treatments for kinesiophobia in people with chronic pain: A scoping review.

Kinesiophobia is associated with pain intensity in people suffering from chronic pain. The number of publications highlighting this relationship has increased significantly in recent years, emphasizing the importance of investigating and synthesizing research evidence on this topic. The purpose of this scoping review was to answer the following questions: (1) What types of interventions have been or are currently being studied in randomized controlled trials (RCTs) for the management of kinesiophobia in patients with chronic pain? (2) What chronic pain conditions are targeted by these interventions? (3) What assessment tools for kinesiophobia are used in these interventions? According to the studies reviewed, (1) physical exercise is the most commonly used approach for managing irrational fear of movement, (2) interventions for kinesiophobia have primarily focused on musculoskeletal pain conditions, particularly low back pain and neck pain, and (3) the Tampa Scale of Kinesiophobia is the most commonly used tool for measuring kinesiophobia. Future RCTs should consider multidisciplinary interventions that can help patients confront their irrational fear of movement while taking into account the patient's personal biological, psychological, and social experiences with pain and kinesiophobia.

Postural Correlates of Pollution Perception.

In our contemporary societies, environmental issues are more and more important. An increasing number of studies explore the biological processes involved in environment perception and in particular try to highlight the mechanisms underlying the perception of environmental scenes by our brain. The main objective of the present study was to establish whether the visualization of clean and polluted environmental scenes would lead to differential postural reactions. Our hypothesis was based on a differential postural modulation that could be recorded when the subject is confronted with images representing a "polluted" environment, differential modulation which has been reported in previous studies in response to painful-scenes compared to non-painful scenes visualization.Thirty-one subjects participated in this study. Physiological measurements [heart rate variability (HRV) and electrodermal activity] and postural responses (Center Of Pression-COP-displacements) were recorded in response to perception of polluted or clean environmental scenes. We show, for the first time, that images representing polluted scenes evoke a weaker approach movement than images representing clean scenes. The displacement of the COP in the anteroposterior axis reflects an avoidance when subjects visualize "polluted" scenes. Our results demonstrate a clear distinction between "clean" and "polluted" environments according to the postural change they induce, correlated with the ratings of pleasure and approach evoked by images.

Approach-Avoidance Behavior in the Empathy for Pain Model as Measured by Posturography.

The interrelation between motor and emotional processes has been a recurrent question since several decades in the scientific literature. An interesting experimental technique to explore this question is posturography which assess the modulation of human postural control. In an emerging scientific field, this technique has been used to explore the reaction of the body in different emotional conditions. However, among available studies, some inconsistencies appear. In this brief report, we want to show how a widely used experimental model, i.e., empathy for pain, allowed in several study to provide comprehensive understanding elements on the postural correlates of socioemotional information processing. In particular, the role of mental simulation is discussed.

Effects of specific inspiratory muscle training combined with whole-body endurance training program on balance in COPD patients: Randomized controlled trial.

PURPOSE: This study aims to assess the effect of inspiratory muscle training (IMT) combined with endurance training (ET) on balance in patients with chronic obstructive pulmonary disease (COPD). METHODS: We studied 32 male patients (62 ± 6 years) with moderate to very severe COPD. They were randomly assigned to an experimental group (IMT+ET) n = 16 or a control group (ET) n = 16 with similar characteristics. The evaluations were carried out at inclusion and after eight weeks of the training period. Functional balance was assessed by the Berg Balance Scale (BBS), the Timed-up and Go (TUG), the Single Leg Stance test (SLS), and the Activities-specific Balance Confidence (ABC) scale. The strength of the inspiratory muscles (PImax) was assessed by maximal inspiratory mouth pressure. Functional exercise performance was assessed by the 6 minutes walking test (6MWT). IMT program consists in performing two daily sets of 30 inspirations with 50% of PImax increased by 10% every two weeks. ET program consists in performing 30 min treadmill exercise at 60% to 80% of the average speed achieved during the 6MWT three days per week. RESULTS: After the training period, the experimental group demonstrated greater improvements in BBS (IMT+ET vs. ET; p = 0.019), and in ABC (IMT+ET vs. ET; p = 0.014). However, no significant differences between groups were observed for TUG, SLS, and 6MWT. There was a significant difference between groups in PImax (IMT+ET vs. ET; p = 0.030). Significant moderate correlations were obtained between ΔPImax and ΔBBS for both groups (IMT+ET: r = 0.624, p = 0.010; ET r = 0.550, p = 0.027) as well as for ΔABC but only in the experimental group (IMT+ET: r = 0.550, p = 0.027). CONCLUSION: Compared to ET alone, the results suggest that IMT combined with ET enhances inspiratory muscle function and functional balance according to BBS and ABC in patients with COPD. We suggest that inspiratory muscle training might be introduced as additional training to pulmonary rehabilitation programs aimed at improving balance in COPD patients. TRIAL REGISTRATION: The trial registry name: Clinical Trials; Registration number: NCT04084405; URL: https://clinicaltrials.gov/ct2/show/NCT04084405.

Postural correlates of painful stimuli exposure: impact of mental simulation processes and pain-level of the stimuli.

Previous studies have reported (i) freezing-like posturographic correlates in response to painful as compared to non-painful scenes vision (Lelard et al., Front Hum Neurosci 7:4, 2013) and (ii) an increase of this response during the mental simulation as compared to the passive viewing of the painful scenes (Lelard et al., Front Psychol 8:2012, 2017). The main objective of the present study was to explore the modulation of posturographic correlates of painful scenes vision by the level of depicted pain and the influence of mental simulation on this modulation. Thirty-six participants (36.3 ± 11.4 years old) were included in this study. During the experiment, participants had to stand on a posturographic platform. Three types of static visual stimuli were randomly depicting different pain-level situations: no-pain, low-pain, high-pain. In a first run, participants watched these stimuli passively (passive condition); in a second run, they were asked to "imagine that they were personally experiencing the situations they were about to see" (mental simulation condition). For each picture, subjective ratings were recorded for displeasure and desire to avoid at the end of the posturographic session. Results support an approach-type behavior in response to high-pain stimuli in the passive condition which becomes a withdrawal-type behavior in the mental simulation condition. Moreover, this withdrawal-type behavior is modulated by the level of depicted pain and this modulation does not appear for the subjective data. As a conclusion, these results are in accordance with those of previous studies showing the modulation of posturographic correlates of pain perception by mental simulation and report, for the first time, modulation of this effect by the level of depicted pain. The dichotomy of this modulatory effect between subjective and objective data is discussed as well as the finding of an approach-type behavior towards painful stimuli when passively viewing them becoming a withdrawal-type behavior when mental simulation is applied to the same stimuli.

Distinct Whole-Body Movements in Response to Alcohol and Sexual Content in Alcohol Use Disorder.

BACKGROUND: Spontaneous motor responses of approach and avoidance toward stimuli are important in characterizing psychopathological conditions, including alcohol use disorder (AUD). However, divergent results have been reported, possibly due to confounded parameters (e.g., using a symbolic vs. a sensorimotor task, implementation of approach-avoidance as a measure vs. a manipulation). METHODS: We studied whole-body/posturometric changes by using a sensorimotor measure relying on embodied cognition principles to assess forward (approach) and backward (avoidance) spontaneous leaning movements. Over a 12-second period, 51 male patients with AUD and 29 male control participants were instructed to stand still in response to both alcohol and sexual visual content. Patients with AUD were then divided into "abstainers" and "relapsers," depending on their continuous abstinence at 2 weeks postdischarge (obtained via a telephone follow-up interview). The effects of the group, the stimulus type, the experimental period, and their interactions on the posturometric changes were tested using mixed Analyses of variance (ANOVAs), with a significance threshold set at 0.05. RESULTS: Contrary to our expectations, patients and controls did not show significant difference in their forward/backward micromovements while passively viewing alcohol or sexual content (p > 0.1). However, in line with our hypothesis, patients who relapsed several weeks following discharge from the rehabilitation program were significantly more reactive and more likely to lean back during the first seconds of viewing alcohol cues (p = 0.002). Further, "relapsers" were more likely to lean forward during exposure to sexual content than participants who remained abstinent (p < 0.001). CONCLUSIONS: Among individuals with AUD, there are distinct pattern of spontaneous movements that differentiate "abstainers" and "relapsers," findings that can be understood in light of existing data and theories on action tendencies.

Evoked pleasure and approach-avoidance in response to pollution.

From year-to-year, environment is becoming one of the major concerns of human societies. Few studies have investigated the biological processes involved in environmental scene perception. Here, we initiate a line of research by beginning to study emotional processes involved in this perception. Our results demonstrate a clear distinction between "Clean" and "Polluted" environments according to the pleasure and approach desire ratings they induced. Moreover, women expressed higher pleasure in the "Clean" condition, as did older participants. Finally, rural scenes induced higher pleasure in participants than urban ones.

Postural responses to emotional visual stimuli.

Postural control is a motor skill that allows individuals to interact with their environment. Indeed, in all species, development of postural control is a prerequisite for acquiring further motor abilities. In humans, the maintenance of a bipedal posture plays an important role in interaction with the environment, as it provides a stable postural basis allowing upper limbs and hands to be used to manipulate objects. On the other hand, this bipedal posture induces a constraint in terms of balance, as individuals have to deal with a relatively small base of support enclosed by the surface of the two feet. Biomechanical principles underlying postural control have been studied in great depth, but the effect of emotion on postural control seems to be an emergent topic. Over the last two decades, an exponential number of studies have been published at the interface of affective and social neurosciences. Moreover, the interactions between motor and affective processes are increasingly documented in the scientific literature. In this article, we try to synthetize main recent empirical results that have allowed exploration of the link between body posture and emotional processing.

Importance of Temporal Analyzes for the Exploration of the Posturographic Correlates of Emotional Processing.

Over the last two decades, affective and social neurosciences converged on the study of motor correlates of emotional and motivational information processing. Posturography appeared as a good experimental method to address this question. The use of this method to explore emotional and motivation processing remains recent. Here, we summarize several important arguments showing the importance to explore the temporal aspects of these responses regarding the complexity of the link between emotional information's parameters (such as arousal) and the corresponding neural processes.

Mental Simulation of Painful Situations Has an Impact on Posture and Psychophysiological Parameters.

Embodiment is made possible by the ability to imagine ourselves in a particular situation (mental simulation). Postural changes have been demonstrated in response to painful situations, but the effect of an implicit instruction has not been studied. The present study was designed to record differential responses according to whether or not subjects were instructed to imagine themselves in a painful or non-painful situation. Painful stimuli and instructions to mentally simulate the displayed situation were hypothesized to induce postural changes that could be demonstrated by changes in the center of pressure (COP) trajectory compared to viewing the same stimuli with no instructions. We hypothesized that mental simulation of a painful situation would induce embodiment of the emotional situation as reflected by posterior displacement of the COP and physiological responses as compared to passive observation of the same visual scene. Thirty-one subjects participated in this study while standing quietly on a posturographic platform with presentation of visual stimuli depicting scenes defining three experimental conditions (painful, non-painful and neutral situations) for 12 s. Physiological measurements [heart rate (HR) and electrodermal activity] and postural responses (COP displacements) were recorded in response to the stimuli with or without instructions to imagine themselves in the situation. Time-course analyses (1 s sliding window) were conducted for several postural parameters, HR and electrodermal response. An interaction effect (instruction × stimuli × time) demonstrated that mental simulation induced posterior displacement of the mean position of the COP at different times during presentation of visual stimuli (4 s; 9-12 s). An effect of instruction was reported for HR (HR was higher in the mental simulation condition), while a stimulation effect was reported only for HR (lower for painful stimuli than for non-painful stimuli). The results of time-course analyses demonstrated embodiment of painful situations by postural control modulations and physiological changes depending on whether or not the participants were instructed to imagine themselves in the situation.

Electromyographic Pattern during Gait Initiation Differentiates Yoga Practitioners among Physically Active Older Subjects.

During gait initiation, postural adjustments are needed to deal with balance and movement. With aging, gait initiation changes and reflects functional degradation of frailty individuals. However, physical activities have demonstrated beneficial effects of daily motor tasks. The aim of our study was to compare center of pressure (COP) displacement and ankle muscle co-activation during gait initiation in two physically active groups: a group of walkers (n = 12; mean age ± SD 72.6 ± 3.2 years) and a yoga group (n = 11; 71.5 ± 3.8 years). COP trajectory and electromyography of leg muscles were recorded simultaneously during five successive trials of gait initiation. Our main finding was that yoga practitioners had slower COP displacements (p < 0.01) and lower leg muscles % of coactivation (p < 0.01) in comparison with walkers. These parameters which characterized gait initiation control were correlated (r = 0.76; p < 0.01). Our results emphasize that lengthy ankle muscle co-activation and COP path in gait initiation differentiate yoga practitioners among physically active subjects.

Do we feel the same empathy for loved and hated peers?

Empathy allows us to understand and react to other people's feelings and sensations; we can more accurately judge another person's situation when we are aware of his/her emotions. Empathy for pain is a good working model of the behavioral and neural processes involved in empathy in general. Although the influence of perspective-taking processes (notably "Self" vs. "Other") on pain rating has been studied, the impact of the degree of familiarity with the person representing the "Other" perspective has not been previously addressed. In the present study, we asked participants to adopt four different perspectives: "Self", "Other-Most-Loved-Familiar", "Other-Most-Hated-Familiar" and "Other-Stranger". The results showed that higher pain ratings were attributed to the Other-Most-Loved-Familiar perspective than to the Self, Other-Stranger and Other-Most-Hated-Familiar perspectives. Moreover, participants were quicker to rate pain for the Other-Most-Loved-Familiar perspective and the Self-perspective than for the other two perspectives. These results for a perspective-taking task therefore more clearly define the role of familiarity in empathy for pain.

Freezing behavior as a response to sexual visual stimuli as demonstrated by posturography.

Posturographic changes in motivational conditions remain largely unexplored in the context of embodied cognition. Over the last decade, sexual motivation has been used as a good canonical working model to study motivated social interactions. The objective of this study was to explore posturographic variations in response to visual sexual videos as compared to neutral videos. Our results support demonstration of a freezing-type response in response to sexually explicit stimuli compared to other conditions, as demonstrated by significantly decreased standard deviations for (i) the center of pressure displacement along the mediolateral and anteroposterior axes and (ii) center of pressure's displacement surface. These results support the complexity of the motor correlates of sexual motivation considered to be a canonical functional context to study the motor correlates of motivated social interactions.

Gait cycle and plantar pressure distribution in children with cerebral palsy: clinically useful outcome measures for a management and rehabilitation.

BACKGROUND: Information on altered foot pressures during ambulation would clarify how far limb deformities modify walking patterns in cerebral palsy (CP), and whether such data can inform prognosis and guide rehabilitation. OBJECTIVE: To compare patterns of plantar pressures during walking between children with CP and their able-bodied (AB) peers. METHODS: Twenty-five children/adolescents (10 with hemiplegia, 5 with diplegia, and 10 AB, respective ages 13.0 ± 1.9, 13.0 ± 0.6 and 14.0 ± 0.7 years) walked a 12 m line at a self-selected speed. Spatio-temporal parameters and peak in-shoe plantar pressures were recorded for both feet, using the Parotec analysis system. RESULTS: Walking speeds (m·-1) differed significantly between groups (0.65 ± 0.13, hemiplegia, 0.93 ± 0.22 diplegia and 1.26 ± 0.05 AB), with shorter stride lengths in CP. Contact time, double support time and step duration were also shorter in hemiplegia. Plantar pressures differed substantially and consistently between AB and CP, with increased medial heel pressures in hemiplegia, and reduced hallux and lateral heel pressures but increased lateral, medial mid-foot and first metatarsal pressures in diplegia. CONCLUSIONS: Substantial alterations in spatio-temporal parameters (greater in hemiplegia than in diplegia) and plantar pressure distribution reflect attempts to compensate for poor stability of posture in CP. Further study of these adaptive changes holds clinical promise in providing data relevant to the design of orthotics, determinations of prognosis and the planning of neurorehabilitation.

Reproducibility of gait cycle and plantar pressure distribution in children with spastic hemiplegic cerebral palsy.

BACKGROUND: Gait cycle and pressure distribution patterns can now be recorded quite simply and reproducibly with inexpensive in-sole pressure recorders. However, it is not known whether such readings are sufficiently stable to provide useful information in monitoring children with spastic hemiplegic cerebral palsy (HCP). OBJECTIVE: The aim of this study was to asses the reproducibility of gait cycle and plantar pressure in HCP. METHODS: Fourteen children with HCP (Gross Motor Function Classification System level I or II) undertook two walking trials (4 × 12 meters at self-selected speeds) with a one-week inter-test interval. Spatio-temporal gait cycle parameters and peak plantar pressures were measured at each visit, using Parotec in-shoe pressure sensors. RESULTS: In the unaffected limb, satisfactory reproducibility was found for measurements of velocity, step frequency, time of double support, and step duration, but not for step amplitude or contact time. However, in the affected limb, only velocity and step duration showed moderate reproducibility. Likewise, all of 8 pressure measurements were reproducible for the unaffected limb, but pressures for the affected limb were only consistent at 4 sites (metatarsals 4-5, lateral heel, lateral mid-foot and hallux). CONCLUSIONS: Since plantar pressures are unstable only in the affected limb, the cause of variation is likely immediate spasm during movement of this limb rather than a more permanent change of posture. Some spatio-temporal parameters and plantar pressure readings have sufficient stability in both unaffected and affected limbs to allow their use when evaluating gait and planning therapy for children with HCP.

Influence of postural threat on postural responses to aversive visual stimuli.

Recent research has shown that emotion influences postural control. The objective of the present study was to establish whether or not postural threat influences postural and physiological responses to aversive visual stimuli. In order to investigate the coupling between emotional reactions, motivated behavior and postural responses, we studied the displacement of the subject's center of pressure (COP) and the changes in electrodermal activity (EDA), heart rate (HR) and postural muscle activation. Thirty-two participants (15 males, 17 females; mean ± SD age: 21.4 ± 2.3) viewed affective and neutral pictures while standing still on a force platform in the presence or absence of postural threat. The HR and EDA data revealed that the emotional state varied as a function of the postural condition. The mean displacement in the anteroposterior (AP) axis was more rearwards in response to aversive stimuli that in response to neutral stimuli, in both the absence of postural threat (-0.65 mm and +0.90 mm for aversive and neutral stimuli, respectively) and the presence of postural threat (-0.00 mm vs. +0.89 mm, respectively). An aversive stimulus was associated with a shorter AP COP sway path than a neutral stimulus in the presence of a postural threat (167.26 mm vs. 174.66 mm for aversive and neutral stimuli, respectively) but not in the latter's absence (155.85 mm vs. 154.48 mm, respectively). Our results evidenced withdrawal behavior in response to an aversive stimulus (relative to a neutral stimulus) in the absence of postural threat. Withdrawal behavior was attenuated (but nevertheless active) in the presence of a postural threat.

Postural correlates with painful situations.

BACKGROUND: Emotional context may play a crucial role in movement production. According to simulation theories, emotional states affect motor systems. The aim of this study was to compare postural responses assessed by posturography and electromyography when subjects were instructed to imagine themselves in a painful or a non-painful situation. METHODS: Twenty-nine subjects (22.3 ± 3.7 years) participated in this study. While standing quietly on a posturographic platform, they were instructed to imagine themselves in a painful or non-painful situation. Displacement of the center of pressure (COP), leg muscle electromyographic activity, heart rate, and electrodermal activity were assessed in response to painful and non-painful situations. RESULTS: The anteroposterior path was shorter (p < 0.05) when subjects imagined themselves in a painful situation (M = 148.0 ± 33.4 mm) compared to a non-painful situation (158.2 ± 38.7 mm). Higher tibialis anterior (TA) activity (RMS-TA = 3.38 ± 1.95% vs. 3.24 ± 1.85%; p < 0.001) and higher variability of soleus (SO) activity (variation coefficient of RMS-SO = 13.5 ± 16.2% vs. M = 9.0 ± 7.2%; p < 0.05) were also observed in painful compared to non-painful situations. No significant changes were observed for other physiological data. CONCLUSION: This study demonstrates that simulation of painful situations induces changes in postural control and leg muscle activation compared to non-painful situations, as increased stiffness was demonstrated in response to aversive pictures in accordance with previous results.