Guidelines for reporting action simulation studies (GRASS): Proposals to improve reporting of research in motor imagery and action observation

Researchers from multiple disciplines have studied the simulation of actions through motor imagery, action observation, or their combination. Procedures used in these studies vary considerably between research groups, and no standardized approach to reporting experimental protocols has been proposed. This has led to under-reporting of critical details, impairing the assessment, replication, synthesis, and potential clinical translation of effects. We provide an overview of issues related to the reporting of information in action simulation studies, and discuss the benefits of standardized reporting. We propose a series of checklists that identify key details of research protocols to include when reporting action simulation studies. Each checklist comprises A) essential methodological details, B) essential details that are relevant to a specific mode of action simulation, and C) further points that may be useful on a case-by-case basis. We anticipate that the use of these guidelines will improve the understanding, reproduction, and synthesis of studies using action simulation, and enhance the translation of research using motor imagery and action observation to applied and clinical settings.

Does Tactile Stimulation of the Face Affect the Processing of Other Faces? Neural and Behavioural Effects of Facial Touch

The integration of vision and touch is proposed as a critical factor for processing one's own body and the bodies of others in the brain. We hypothesize that tactile stimulation on an individual's face may change the ability to process the faces of other, but not the processing of other visual images. We aimed to determine if facial touch increased the activity of the mirror system and face recognition memory of the observer. Therefore, mu suppression was measured to compare the effect of facial touch in performing two visual tasks. The participants observed faces and non-face visual images under two sets of conditions. In the first condition, a robotic finger touched the participant's cheek while in the second condition, no touch occurred. Upon each observational task, the participants were given in a recognition test. Behavioral results indicated that facial touch improved recognition performance for faces, but not for non-face visual images. Tactile stimulation increased mu suppression in both occipital and central electrodes during face processing; however, the suppression did not significantly change during non-face visual processing. Our findings support the concept that the brain uses a self-body representation, as a reference to understand the mental states or behaviors of others.

The degree of mu rhythm suppression in women is associated with presence of children as well as empathy and anxiety level

In experiments on observing and performing social gestures, the level of mu rhythm suppression is associated with the activity of the mirror neuron system (MNS), which is responsible for the perception and understanding of nonverbal signals in social communication. In turn, while MNS activity may be associated primarily with empathy, it is also associated with other psychological and demographic factors affecting the effectiveness of cortical neural networks.In this study, we verified the influence of empathy, state and trait anxiety levels, presence and number of children, age, and menstrual cycle phase on the mu-suppression level in 40 women. We used 32-channel EEG recorded during observation, and synchronous execution of various hand movements. The ICA infomax method was used for decomposing and selecting the left hemisphere component of the mu-rhythm.Mu-suppression was higher in women with one child, with higher levels of empathy, and with lower anxiety levels. It is possible that MNS activity is stronger in women during parental care.

The Transdiagnostic Relevance of Self-Other Distinction to Psychiatry Spans Emotional, Cognitive and Motor Domains

Self-other distinction refers to the ability to distinguish between our own and other people's physical and mental states (actions, perceptions, emotions etc.). Both the right temporo-parietal junction and brain areas associated with the human mirror neuron system are likely to critically influence self-other distinction, given their respective contributions to theory of mind and embodied empathy. The degree of appropriate self-other distinction will vary according to the exact social situation, and how helpful it is to feel into, or remain detached from, another person's mental state. Indeed, the emotional resonance that we can share with others affords the gift of empathy, but over-sharing may pose a downside, leading to a range of difficulties from personal distress to paranoia, and perhaps even motor tics and compulsions. The aim of this perspective paper is to consider how evidence from behavioral and neurophysiological studies supports a role for problems with self-other distinction in a range of psychiatric symptoms spanning the emotional, cognitive and motor domains. The various signs and symptoms associated with problematic self-other distinction comprise both maladaptive and adaptive (compensatory) responses to dysfunction within a common underlying neuropsychological mechanism, compelling the adoption of more holistic transdiagnostic therapeutic approaches within Psychiatry.

Bridging the gap between emotion and joint action

Our daily human life is filled with a myriad of joint action moments, be it children playing, adults working together (i.e., team sports), or strangers navigating through a crowd. Joint action brings individuals (and embodiment of their emotions) together, in space and in time. Yet little is known about how individual emotions propagate through embodied presence in a group, and how joint action changes individual emotion. In fact, the multi-agent component is largely missing from neuroscience-based approaches to emotion, and reversely joint action research has not found a way yet to include emotion as one of the key parameters to model socio-motor interaction. In this review, we first identify the gap and then stockpile evidence showing strong entanglement between emotion and acting together from various branches of sciences. We propose an integrative approach to bridge the gap, highlight five research avenues to do so in behavioral neuroscience and digital sciences, and address some of the key challenges in the area faced by modern societies.

Social Feedback During Sensorimotor Synchronization Changes Salivary Oxytocin and Behavioral States

In humans and animal models, oxytocin increases social closeness, attachment and prosocial behaviors, while decreasing anxiety and stress levels. Efficiently triggering the release of endogenous oxytocin could serve as a powerful therapeutic intervention for disorders of social behavior and for anxiety. We designed a new version of a social sensorimotor synchronization task to investigate the role of social approval in inducing biochemical and psychological changes following behavioral synchrony in a sample of 80 college students. Social approval in the form of real time positive feedback increased well-being only in women, while increasing social closeness in both genders. Social disapproval in the form of real time negative feedback prevented a decrease in stress levels that otherwise women reported following engagement in either social or non-social synchronization. Surprisingly, for certain personality traits, negative social feedback during sensorimotor synchronization was psychologically beneficial irrespective of gender. Salivary oxytocin levels increased only in women after the social but not the non-social synchronization tasks. Oxytocin dynamics were independent of the type of real time feedback that subjects received, indicating the existence of distinct mechanisms for hormonal versus behavioral changes following synchronization. Nevertheless, changes in salivary oxytocin after positive social feedback correlated with changes in well-being and predicted changes in prosocial attitudes. Our findings show evidence of distinct mechanisms for behavioral versus hormonal changes following social sensorimotor synchronization, and indicate that gender and personality traits should be carefully considered when designing behavioral therapies for improving social attitudes and for stress management.

I'll cry instead: Mu suppression responses to tearful facial expressions

Tears are a facial expression of emotion that readily elicit empathic responses from observers. It is currently unknown whether these empathic responses to tears are influenced by specific neural substrates. The EEG mu rhythm is one method of investigating the human mirror neuron system, purported to underlie the sharing of affective states and a facilitator of social cognition. The purpose of this research was to explore the mu response to tearful expressions of emotion. Sixty-eight participants viewed happy and sad faces, both with and without tears, in addition to a neutral control condition. Participants first completed an emotion discrimination task, and then an imitation condition where they were required to mimic the displayed expression. Mu enhancement was found in response to the discrimination task, whilst suppression was demonstrated in response to the imitation condition. Examination of the suppression scores revealed that greater suppression was observed in response to happy-tear and sad tear-free expressions. Planned contrasts exploring suppression to neutral faces revealed no significant differences between emotional and neutral conditions. The mu response to neutral expressions resembled that of the happy-tear and the sad tear-free conditions, lending support to the idea that ambiguous emotional expressions require greater sensorimotor engagement. This study provides preliminary evidence for the role of the mirror neuron system in discerning tearful expressions of emotion in the absence of context.

Social perceptions of warmth and competence influence behavioral intentions and neural processing

Perceptions of the primary social dimensions, warmth and competence, determine how we view and relate to social targets. To discern how warmth and competence might affect neural processing and its downstream behavioral consequences, we manipulated impressions of targets' warmth and competence and then measured intentions toward the target and motor resonance, a neural process previously linked to social processing. While EEG was recorded, 66 participants watched videos of people performing a simple motor activity and completed a measure of hypothetical intentions to help or harm. Both perceptions of warmth and competence predicted an increase in helping intentions. Moreover, participants showed the least motor resonance with high competence-medium warmth targets, suggesting the importance of both social dimensions in driving neural simulation of targets' actions. Perceptions of a person's warmth and competence can affect not only how others might intend to treat them, but also how they might process their basic experiences on a neural level.

Electrophysiological indicators of gesture perception

Electroencephalography (EEG) activity in the mu frequency band (8-13 Hz) is suppressed during both gesture performance and observation. However, it is not clear if or how particular characteristics within the kinematic execution of gestures map onto dynamic changes in mu activity. Mapping the time course of gesture kinematics onto that of mu activity could help understand which aspects of gestures capture attention and aid in the classification of communicative intent. In this work, we test whether the timing of inflection points within gesture kinematics predicts the occurrence of oscillatory mu activity during passive gesture observation. The timing for salient features of performed gestures in video stimuli was determined by isolating inflection points in the hands' motion trajectories. Participants passively viewed the gesture videos while continuous EEG data was collected. We used wavelet analysis to extract mu oscillations at 11 Hz and at central electrodes and occipital electrodes. We used linear regression to test for associations between the timing of inflection points in motion trajectories and mu oscillations that generalized across gesture stimuli. Separately, we also tested whether inflection point occurrences evoked mu/alpha responses that generalized across participants. Across all gestures and inflection points, and pooled across participants, peaks in 11 Hz EEG waveforms were detected 465 and 535 ms after inflection points at occipital and central electrodes, respectively. A regression model showed that inflection points in the motion trajectories strongly predicted subsequent mu oscillations ([Formula: see text]<0.01); effects were weaker and non-significant for low (17 Hz) and high (21 Hz) beta activity. When segmented by inflection point occurrence rather than stimulus onset and testing participants as a random effect, inflection points evoked mu and beta activity from 308 to 364 ms at central electrodes, and broad activity from 226 to 800 ms at occipital electrodes. The results suggest that inflection points in gesture trajectories elicit coordinated activity in the visual and motor cortices, with prominent activity in the mu/alpha frequency band and extending into the beta frequency band. The time course of activity indicates that visual processing drives subsequent activity in the motor cortex during gesture processing, with a lag of approximately 80 ms.

Mimicking emotions

Emotional mimicry refers to the tendency to mimic other's emotions in order to share minds. We present new evidence that supports our Contextual Model of Emotional Mimicry, showing that emotional mimicry serves affiliative goals that vary across social contexts. This also implies the opposite, namely that we (unconsciously) refrain from mimicking others' emotions if we want to keep emotional distance. Facial mimicry of emotions is further suggested to be a largely top-down process, based on goals and representations, rather than on mere watching others' facial movements.

Reduced reward-related neural response to mimicry in individuals with autism

Mimicry is a facilitator of social bonds in humans, from infancy. This facilitation is made possible through changing the reward value of social stimuli; for example, we like and affiliate more with people who mimic us. Autism spectrum disorders (ASD) are marked by difficulties in forming social bonds. In this study, we investigate whether the reward-related neural response to being mimicked is altered in individuals with ASD, using a simple conditioning paradigm. Multiple studies in humans and nonhuman primates have established a crucial role for the ventral striatal (VS) region in responding to rewards. In this study, adults with ASD and matched controls first underwent a conditioning task outside the scanner, where they were mimicked by one face and 'anti-mimicked' by another. In the second part, participants passively viewed the conditioned faces in a 3T MRI scanner using a multi-echo sequence. The differential neural response towards mimicking vs. anti-mimicking faces in the VS was tested for group differences as well as an association with self-reported autistic traits. Multiple regression analysis revealed lower left VS response to mimicry (mimicking > anti-mimicking faces) in the ASD group compared to controls. The VS response to mimicry was negatively correlated with autistic traits across the whole sample. Our results suggest that for individuals with ASD and high autistic traits, being mimicked is associated with lower reward-related neural response. This result points to a potential mechanism underlying the difficulties reported by many of individuals with ASD in building social rapport.

Testing the relationship between mimicry, trust and rapport in virtual reality conversations

People mimic each other’s actions and postures during everyday interactions. It is widely believed this mimicry acts as a social glue, leading to increased rapport. We present two studies using virtual reality to rigorously test this hypothesis. In Study 1, 50 participants interacted with two avatars who either mimicked their head and torso movements at a 1 or 3 second time delay or did not mimic, and rated feelings of rapport and trust toward the avatars. Rapport was higher towards mimicking avatars, with no effect of timing. In Study 2, we aimed to replicate this effect in a pre-registered design and test whether it is modulated by cultural ingroup-outgroup boundaries. Forty participants from European or East Asian backgrounds interacted with four avatars, two of European appearance and two of East Asian appearance. Two avatars mimicked while the other two did not. We found no effects of mimicry on rapport or trust ratings or implicit trust behaviour in a novel maze task, and no effects of group status or interactions. These null results were calculated in line with our pre-registration. We conclude that being mimicked does not always increase rapport or trust, and make suggestions for future directions.

Holding Biological Motion in Working Memory: An fMRI Study

Holding biological motion (BM), the movements of animate entities, in working memory (WM) is important to our daily life activities. However, the neural substrates underlying the WM processing of BM remain largely unknown. Employing the functional magnetic resonance imaging (fMRI) technique, the current study directly investigated this issue. We used point-light BM animations as the tested stimuli, and explored the neural substrates involved in encoding and retaining BM information in WM. Participants were required to remember two or four BM stimuli in a change-detection task. We first defined a set of potential brain regions devoted to the BM processing in WM in one experiment. We then conducted the second fMRI experiment, and performed time-course analysis over the pre-defined regions, which allowed us to differentiate the encoding and maintenance phases of WM. The results showed that a set of brain regions were involved in encoding BM into WM, including the middle frontal gyrus, inferior frontal gyrus, superior parietal lobule, inferior parietal lobule, superior temporal sulcus, fusiform gyrus, and middle occipital gyrus. However, only the middle frontal gyrus, inferior frontal gyrus, superior parietal lobule, and inferior parietal lobule were involved in retaining BM into WM. These results suggest that an overlapped network exists between the WM encoding and maintenance for BM; however, retaining BM in WM predominately relies on the mirror neuron system.

Social class affects Mu-suppression during action observation

Socioeconomic status (SES) has been linked to differences in the degree to which people are attuned to others. Those who are lower in SES also tend to be more interpersonally attuned. However, to date, this work has not been demonstrated using neural measures. In the present electroencephalogram study, we found evidence that lower SES was linked to stronger Mu-suppression during action observation. This finding adds to the growing literature on factors that affect Mu-suppression and suggests that the mirror neuron system may be influenced by one's social class.

The coordination dynamics of social neuromarkers

Social behavior is a complex integrative function that entails many aspects of the brain’s sensory, cognitive, emotional and movement capacities. Its neural processes are seldom simultaneous but occur according to precise spatiotemporal choreographies, manifested by the coordination of their oscillations within and between brains. Methods with good temporal resolution can help to identify so-called “neuromarkers” of social function and aid in disentangling the dynamical architecture of social brains. In our ongoing research, we have used dual-electroencephalography (EEG) to study neuromarker dynamics during synchronic interactions in which pairs of subjects coordinate behavior spontaneously and intentionally (social coordination) and during diachronic transactions that require subjects to perceive or behave in turn (action observation, delayed imitation). In this paper, after outlining our dynamical approach to the neurophysiological basis of social behavior, we examine commonalities and differences in the neuromarkers that are recruited for both kinds of tasks. We find the neuromarker landscape to be task-specific: synchronic paradigms of social coordination reveal medial mu, alpha and the phi complex as contributing neuromarkers. Diachronic tasks recruit alpha as well, in addition to lateral mu rhythms and the newly discovered nu and kappa rhythms whose functional significance is still unclear. Social coordination, observation, and delayed imitation share commonality of context: in each of our experiments, subjects exchanged information through visual perception and moved in similar ways. Nonetheless, there was little overlap between their neuromarkers, a result that hints strongly of task-specific neural mechanisms for social behavior. The only neuromarker that transcended both synchronic and diachronic social behaviors was the ubiquitous alpha rhythm, which appears to be a key signature of visually-mediated social behaviors. The present paper is both an entry point and a challenge: much work remains to determine the nature and scope of recruitment of other neuromarkers, and to create theoretical models of their within- and between-brain dynamics during social interaction.

When mirroring is both simple and "smart": how mimicry can be embodied, adaptive, and non-representational

The concept of mirroring has become rather ubiquitous. One of the most fundamental empirical and theoretical debates within research on mirroring concerns the role of mental representations: while some models argue that higher-order representational mechanisms underpin most cases of mirroring, other models argue that they only moderate a primarily non-representational process. As such, even though research on mirroring—along with its neural substrates, including the putative mirror neuron system—has grown tremendously, so too has confusion about what it actually means to “mirror”. Using recent research on spontaneous imitation, we argue that flexible mirroring effects can be fully embodied and dynamic—even in the absence of higher-order mental representations. We propose that mirroring can simply reflect an adaptive integration and utilization of cues obtained from the brain, body, and environment, which is especially evident within the social context. Such a view offers reconciliation among both representational and non-representational frameworks in cognitive neuroscience, which will facilitate revised interpretations of modern (and seemingly divergent) findings on when and how these embodied mirroring responses are employed.