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.

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.

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.

Importance of the "thinking through other minds" process explored through motor correlates of motivated social interactions.

We wanted to gather recent results supporting the idea of the central role of sharing agency in socioaffective and motivational information processing. Here, we want to support the idea that this process is quite arbitrary, early in the temporal chain of processes and not only influence the psychological, but also the motor correlates of socioaffective information processes.

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.

Does impaired socioemotional functioning account for behavioral dysexecutive disorders? Evidence from a transnosological study.

Behavioral dysexecutive disorders are highly prevalent in patients with neurological diseases but cannot be explained by cognitive dysexecutive impairments. In fact, the underlying mechanisms are poorly understood. Given that socioemotional functioning underlies appropriate behavior, socioemotional impairments may contribute to the appearance of behavioral disorders. To investigate this issue, we performed a transnosological study. Seventy-five patients suffering from various neurological diseases (Alzheimer's disease (AD), Parkinson's disease (PD), frontotemporal lobar degeneration, and stroke) were included in the study. The patients were comprehensively assessed in terms of cognitive and behavioral dysexecutive disorders and socioemotional processes (facial emotion recognition and theory of mind). As was seen for cognitive and behavioral dysexecutive impairments, the prevalence of socioemotional impairments varied according to the diagnosis. Stepwise logistic regressions showed that (i) only cognitive executive indices predicted hypoactivity with apathy/abulia, (ii) theory of mind impairments predicted hyperactivity-distractibility-impulsivity and stereotyped/perseverative behaviors, and (iii) impaired facial emotion recognition predicted social behavior disorders. Several dysexecutive behavioral disorders are associated with an underlying impairment in socioemotional processes but not with cognitive indices of executive functioning (except for apathy). These results strongly suggest that some dysexecutive behavioral disorders are the outward signs of an underlying impairment in socioemotional processes.

Empathy or Ownership? Evidence from Corticospinal Excitability Modulation during Pain Observation.

Recent studies show that motor responses similar to those present in one's own pain (freezing effect) occur as a result of observation of pain in others. This finding has been interpreted as the physiological basis of empathy. Alternatively, it can represent the physiological counterpart of an embodiment phenomenon related to the sense of body ownership. We compared the empathy and the ownership hypotheses by manipulating the perspective of the observed hand model receiving pain so that it could be a first-person perspective, the one in which embodiment occurs, or a third-person perspective, the one in which we usually perceive the others. Motor-evoked potentials (MEPs) by TMS over M1 were recorded from first dorsal interosseous muscle, whereas participants observed video clips showing (a) a needle penetrating or (b) a Q-tip touching a hand model, presented either in first-person or in third-person perspective. We found that a pain-specific inhibition of MEP amplitude (a significantly greater MEP reduction in the "pain" compared with the "touch" conditions) only pertains to the first-person perspective, and it is related to the strength of the self-reported embodiment. We interpreted this corticospinal modulation according to an "affective" conception of body ownership, suggesting that the body I feel as my own is the body I care more about.

Effect of arousal on perception as studied through the lens of the motor correlates of sexual arousal.

The study of sexual arousal is at the interface of affective and social neurosciences. Recent results regarding the motor correlates of sexual arousal demonstrating an early freezing response are in perfect accordance with the GANE (glutamate amplifies noradrenergic effects) model's sustaining the double role of the arousal dimension on emotional processing.

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.

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.

Theory of mind and hypomanic traits in general population.

Theory of Mind (ToM) is the ability to assign a set of mental states to yourself and others. In bipolar disorders, alteration of social relationship can be explained by the impairment of the functioning of ToM. Deficit in ToM could be a trait marker of bipolar disorder and people in the general population with high hypomanic personality scores would be more likely to develop bipolar disorders. This study examined 298 participants. Measures of hypomanic personality were evaluated using the Hypomanic Personality Scale. ToM was explored using the Yoni task. Participants also completed the BDI-II. Forward multiple regressions were performed to examine the effect of components of the HPS on the total score in the ToM task. In the women's group, no subscales of the HPS were included in the model. Conversely, the analyses performed on men revealed that the mood vitality and excitement subscale was a significant predictor of ToM abilities. Our study is the first to show the impact of certain dimensions of hypomanic personality on performance in ToM in a male sample. This result supports the idea that deficits in ToM can be a trait marker of bipolar disorder in a healthy male population.

Assessment of socioemotional processes facilitates the distinction between frontotemporal lobar degeneration and Alzheimer's disease.

We explored the value of a battery of socioemotional tasks for differentiating between frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). Patients with FTLD (n = 13) or AD (n = 13) and healthy controls (n = 26) underwent a neuropsychological assessment and the socioemotional battery (an empathy questionnaire, an emotion recognition task, and theory of mind tasks). Socioemotional processes were markedly impaired in FTLD but relatively unaffected in mild AD. The computed Socioemotional Index discriminated more accurately between FTLD from AD than behavioral and executive assessments did. Furthermore, impairments in socioemotional processes were correlated with indifference to others.