Lateralization of the expression of facial emotion in humans

Motor-sensory biases are associated with cognitive and social abilities in humans

Across vertebrates, adaptive behaviors, like feeding and avoiding predators, are linked to lateralized brain function. The presence of the behavioral manifestations of these biases are associated with increased task success. Additionally, when an individual's direction of bias aligns with the majority of the population, it is linked to social advantages. However, it remains unclear if behavioral biases in humans correlate with the same advantages. This large-scale study (N = 313-1661, analyses dependent) examines whether the strength and alignment of behavioral biases associate with cognitive and social benefits respectively in humans. To remain aligned with the animal literature, we evaluate motor-sensory biases linked to motor-sequencing and emotion detection to assess lateralization. Results reveal that moderate hand lateralization is positively associated with task success and task success is, in turn, associated with language fluency, possibly representing a cascade effect. Additionally, like other vertebrates, the majority of our human sample possess a 'standard' laterality profile (right hand bias, left visual bias). A 'reversed' profile is rare by comparison, and associates higher self-reported social difficulties and increased rate of autism and/or attention deficit hyperactivity disorder. We highlight the importance of employing a comparative theoretical framing to illuminate how and why different laterization profiles associate with diverging social and cognitive phenotypes.

Genetic and environmental contributions to gaze lateralization across social and non-social stimuli in human infants

A tendency to look at the left side of faces from the observer's point of view has been found in older children and adults, but it is not known when this face-specific left gaze bias develops and what factors may influence individual differences in gaze lateralization. Therefore, the aims of this study were to estimate gaze lateralization during face observation and to more broadly estimate lateralization tendencies across a wider set of social and non-social stimuli, in early infancy. In addition, we aimed to estimate the influence of genetic and environmental factors on lateralization of gaze. We studied gaze lateralization in 592 5-month-old twins (282 females, 330 monozygotic twins) by recording their gaze while viewing faces and two other types of stimuli that consisted of either collections of dots (non-social stimuli) or faces interspersed with objects (mixed stimuli). A right gaze bias was found when viewing faces, and this measure was moderately heritable (A = 0.38, 95% CI 0.24; 0.50). A left gaze bias was observed in the non-social condition, while a right gaze bias was found in the mixed condition, suggesting that there is no general left gaze bias at this age. Genetic influence on individual differences in gaze lateralization was only found for the tendency to look at the right versus left side of faces, suggesting genetic specificity of lateralized gaze when viewing faces.

Reactivity of the ventromedial prefrontal cortex, but not the amygdala, to negative emotion faces predicts greed personality trait

This study explored whether amygdala reactivity predicted the greed personality trait (GPT) using both task-based and resting-state functional connectivity analyses (ntotal = 452). In Cohort 1 (n = 83), task-based functional magnetic resonance imaging (t-fMRI) results from a region-of-interest (ROI) analysis revealed no direct correlation between amygdala reactivity to fearful and angry faces and GPT. Instead, whole-brain analyses revealed GPT to robustly negatively vary with activations in the right ventromedial prefrontal cortex (vmPFC), supramarginal gyrus, and angular gyrus in the contrast of fearful + angry faces > shapes. Moreover, task-based psychophysiological interaction (PPI) analyses showed that the high GPT group showed weaker functional connectivity of the vmPFC seed with a top-down control network and visual pathways when processing fearful or angry faces compared to their lower GPT counterparts. In Cohort 2, resting-state functional connectivity (rs-FC) analyses indicated stronger connectivity between the vmPFC seed and the top-down control network and visual pathways in individuals with higher GPT. Comparing the two cohorts, bilateral amygdala seeds showed weaker associations with the top-down control network in the high group via PPI analyses in Cohort 1. Yet, they exhibited distinct rs-FC patterns in Cohort 2 (e.g., positive associations of GPT with the left amygdala-top-down network FC but negative associations with the right amygdala-visual pathway FC). The study underscores the role of the vmPFC and its functional connectivity in understanding GPT, rather than amygdala reactivity.

Comparison of Mandibular Volume and Linear Measurements in Patients with Mandibular Asymmetry

In patients with mandibular asymmetry, the volume of the mandible divided by the mandibular median plane is significantly larger on the non-deviated (N-Dev) side than on the deviated (Dev) side. However, it has been reported that there is no significant difference between the volumes of the N-Dev and Dev sides when the mandibular ramus and body are divided. The purpose of this study was to investigate which region is responsible for the volume difference between the N-Dev and Dev sides. Cone Beam Computed Tomography (CBCT) images of patients with mandibular asymmetry were analyzed by measuring the volume, and linear analysis of the mandibular body, ramus, and condyle on the N-Dev and Dev side was performed. In this study, CBCT images of 37 patients (8 Japanese, 16 Korean, and 13 Egyptian) aged ≥ 18 years with mandibular asymmetry (men: 20, women: 17) were used to evaluate mandibular asymmetry. In patients with mandibular asymmetry, the N-Dev side showed significantly larger values than the Dev side for both volume and linear condyle, ramus, and mandibular body measurements. These results do not differ according to sex or ethnicity. Therefore, it is suggested that the N-Dev side of mandibular asymmetry is large without any regional specificity in pathophysiology.

Can Ponies (Equus Caballus) Distinguish Human Facial Expressions?

Communication within a species is essential for access to resources, alerting to dangers, group facilitation and social bonding; human facial expressions are considered to be an important factor in one’s ability to communicate with others. Evidence has shown that dogs and horses are able to distinguish positive and negative facial expressions by observing photographs of humans, however there is currently no research on how facial expressions from a live human are perceived by horses. This study investigated how ponies distinguish facial expressions presented by live actors. Trained actors (n = 2), using the human Facial Action Coding System, displayed four facial expressions (anger, sadness, joy and neutral) individually to twenty ponies. Heart rate and behaviors of the ponies including first monocular eye look, eye look duration (right and left side bias) and latency to approach were observed. A generalized linear mixed model (GLIMMIX) using Sidak’s multiple comparisons of least squared means determined that when exposed to anger expressions ponies looked more often with their left eye first and when exposed to joy, looked more often with their right eye first (p = 0.011). The ponies spent more time looking at angry expressions (p = 0.0003) in comparison to other expressions. There was no variation in heart rate across expressions (p > 0.89). Regardless of human facial expression, ponies looked longer (p = 0.0035), took longer to approach (p = 0.0297) and displayed more oral behaviours (p < 0.0001) with one actor than the other indicating increased arousal or negative valence. Ponies with more experience as a lesson mount had lower heart rates (p < 0.0001) carried their head lower (p < 0.0001), kept their left ear on the actor (p < 0.03) and exhibited more oral behaviours (p < 0.0001) than ponies with less experience. This study demonstrates that ponies are able to distinguish facial expressions presented by a live human, but other factors also contribute to their responses to humans.

A short review on emotion processing: a lateralized network of neuronal networks

Emotions are valenced mental responses and associated physiological reactions that occur spontaneously and automatically in response to internal or external stimuli, and can influence our behavior, and can themselves be modulated to a certain degree voluntarily or by external stimuli. They are subserved by large-scale integrated neuronal networks with epicenters in the amygdala and the hippocampus, and which overlap in the anterior cingulate cortex. Although emotion processing is accepted as being lateralized, the specific role of each hemisphere remains an issue of controversy, and two major hypotheses have been proposed. In the right-hemispheric dominance hypothesis, all emotions are thought to be processed in the right hemisphere, independent of their valence or of the emotional feeling being processed. In the valence lateralization hypothesis, the left is thought to be dominant for the processing of positively valenced stimuli, or of stimuli inducing approach behaviors, whereas negatively valenced stimuli, or stimuli inducing withdrawal behaviors, would be processed in the right hemisphere. More recent research points at the existence of multiple interrelated networks, each associated with the processing of a specific component of emotion generation, i.e., its generation, perception, and regulation. It has thus been proposed to move from hypotheses supporting an overall hemispheric specialization for emotion processing toward dynamic models incorporating multiple interrelated networks which do not necessarily share the same lateralization patterns.

Handedness in ADHD: Meta-Analyses

Meta-analyses have shown that several neurodevelopmental and psychiatric disorders, such as autism spectrum disorder and schizophrenia, are associated with a higher prevalence of atypical (left-, non-right-, or mixed-) handedness. One neurodevelopmental disorder for which this association is unclear is attention deficit hyperactivity disorder (ADHD). Here, some empirical studies have found evidence for a higher prevalence of atypical handedness in individuals with ADHD compared to neurotypical individuals. However, other studies failed to establish such an association. Therefore, meta-analytic integration is critical to estimate whether or not there is an association between handedness and ADHD. We report the results of three meta-analyses (left-, mixed-, and non-right-handedness) comparing handedness in individuals with ADHD to controls (typically developing individuals). The results show evidence of a trend towards elevated levels of atypical handedness when it comes to differences in left- and mixed-handedness (p = 0.09 and p = 0.07, respectively), but do show clear evidence of elevated levels of non-right-handedness between individuals with ADHD and controls (p = 0.02). These findings are discussed in the context of the hypothesis that ADHD is a disorder in which mostly right-hemispheric brain networks are affected. Since right-handedness represents a dominance of the left motor cortex for fine motor behavior, such as writing, as well as a left-hemispheric dominance for language functions, and about 90% of individuals are right-handers, this hypothesis might explain why there is not stronger evidence for an association of left-handedness with ADHD. We suggest that the mechanisms involved in the pathogenesis of ADHD might show an overlap with the mechanisms involved in handedness strength, but not handedness direction.

Context-Dependent Gestural Laterality: A Multifactorial Analysis in Captive Red-Capped Mangabeys

Catarrhine primates gesture preferentially with their right hands, which led to the hypothesis of a gestural origin of human left-hemispheric specialization for language. However, the factors influencing this gestural laterality remain understudied in non-hominoid species, particularly in intraspecific contexts, although it may bring valuable insights into the proximate and ultimate causes of language lateralization. We present here a preliminary investigation of intraspecific gestural laterality in catarrhine monkeys, red-capped mangabeys (Cercocebus torquatus). We described the spontaneous production of brachio-manual intentional gestures in twenty-five captive subjects. Although we did not evidence any significant gestural lateralization neither at the individual- nor population-level, we found that mangabeys preferentially use their right hands to gesture in negative social contexts, such as aggressions, suggesting an effect of emotional lateralization, and that they adapt to the position of their receiver by preferentially using their ipsilateral hand to communicate. These results corroborate previous findings from ape studies. By contrast, factors related to gesture form and socio-demographic characteristics of signaler and receiver did not affect gestural laterality. To understand better the relationships between gestural laterality and brain lateralization from an evolutionary perspective, we suggest that the gestural communication of other monkey species should be examined with a multifactorial approach.

Limb Preference in Animals: New Insights into the Evolution of Manual Laterality in Hominids

Until the 1990s, the notion of brain lateralization—the division of labor between the two hemispheres—and its more visible behavioral manifestation, handedness, remained fiercely defined as a human specific trait. Since then, many studies have evidenced lateralized functions in a wide range of species, including both vertebrates and invertebrates. In this review, we highlight the great contribution of comparative research to the understanding of human handedness’ evolutionary and developmental pathways, by distinguishing animal forelimb asymmetries for functionally different actions—i.e., potentially depending on different hemispheric specializations. Firstly, lateralization for the manipulation of inanimate objects has been associated with genetic and ontogenetic factors, with specific brain regions’ activity, and with morphological limb specializations. These could have emerged under selective pressures notably related to the animal locomotion and social styles. Secondly, lateralization for actions directed to living targets (to self or conspecifics) seems to be in relationship with the brain lateralization for emotion processing. Thirdly, findings on primates’ hand preferences for communicative gestures accounts for a link between gestural laterality and a left-hemispheric specialization for intentional communication and language. Throughout this review, we highlight the value of functional neuroimaging and developmental approaches to shed light on the mechanisms underlying human handedness.

Characterization of stimulus response curves obtained with transcranial magnetic stimulation from bilateral anterior digastric muscles in healthy subjects

PURPOSE

The purpose of the study was to describe measurements of stimulus-response curves in the anterior digastric muscle (ADM) bilaterally following transcranial magnetic stimulation (TMS) to the right and left hemispheres. The first dorsal interosseous muscle (FDI) was the control muscle.

MATERIALS AND METHODS

The subjects were 20 healthy young adults. Test sessions determined motor thresholds (MT) and stimulus-response curves (1.0, 1.2, 1.4, 1.6 × MT) from either the FDI or ADM following TMS to left and right hemispheres using the double cone coil. Bilateral recordings of MEPs in the left and right ADM allowed us to generate stimulus response curves following ipsilateral and contralateral TMS.

RESULTS

Intraclass correlation coefficients (ICC) for MEP amplitudes from ipsilateral and contralateral ADMs were >0.60 at motor threshold (MT) and >0.90 at stimulus intensities above MT. There was a linear increase in MEP amplitudes across stimulus intensities for the FDI following contralateral TMS, while MEP amplitudes from the ADM following contralateral and ipsilateral TMS increased linearly across stimulus intensities [F_{(3, 57) [Muscle × Recording Site × Stim Intensity]} = 33.57; p < 0.05]; (ηp2 = 0.64). The slopes of the stimulus-response curve of the contralateral FDI was greater than the slopes of the stimulus response curves of the ipsilateral and contralateral ADM (p < 0.05).

CONCLUSIONS

The current study provided insights on the methodology for recording stimulus response curves in the ADM with TMS. These findings may translate into a valid, reliable, and relevant clinical outcome to study the pathophysiology of the corticobulbar motor system.

Facial expressions can be categorized along the upper-lower facial axis, from a perceptual perspective

A critical question, fundamental for building models of emotion, is how to categorize emotions. Previous studies have typically taken one of two approaches: (a) they focused on the pre-perceptual visual cues, how salient facial features or configurations were displayed; or (b) they focused on the post-perceptual affective experiences, how emotions affected behavior. In this study, we attempted to group emotions at a peri-perceptual processing level: it is well known that humans perceive different facial expressions differently, therefore, can we classify facial expressions into distinct categories in terms of their perceptual similarities? Here, using a novel non-lexical paradigm, we assessed the perceptual dissimilarities between 20 facial expressions using reaction times. Multidimensional-scaling analysis revealed that facial expressions were organized predominantly along the upper-lower face axis. Cluster analysis of behavioral data delineated three superordinate categories, and eye-tracking measurements validated these clustering results. Interestingly, these superordinate categories can be conceptualized according to how facial displays interact with acoustic communications: One group comprises expressions that have salient mouth features. They likely link to species-specific vocalization, for example, crying, laughing. The second group comprises visual displays with diagnosing features in both the mouth and the eye regions. They are not directly articulable but can be expressed prosodically, for example, sad, angry. Expressions in the third group are also whole-face expressions but are completely independent of vocalization, and likely being blends of two or more elementary expressions. We propose a theoretical framework to interpret the tripartite division in which distinct expression subsets are interpreted as successive phases in an evolutionary chain.

The spatial distribution of eye movements predicts the (false) recognition of emotional facial expressions

Recognizing facial expressions of emotions is a fundamental ability for adaptation to the social environment. To date, it remains unclear whether the spatial distribution of eye movements predicts accurate recognition or, on the contrary, confusion in the recognition of facial emotions. In the present study, we asked participants to recognize facial emotions while monitoring their gaze behavior using eye-tracking technology. In Experiment 1a, 40 participants (20 women) performed a classic facial emotion recognition task with a 5-choice procedure (anger, disgust, fear, happiness, sadness). In Experiment 1b, a second group of 40 participants (20 women) was exposed to the same materials and procedure except that they were instructed to say whether (i.e., Yes/No response) the face expressed a specific emotion (e.g., anger), with the five emotion categories tested in distinct blocks. In Experiment 2, two groups of 32 participants performed the same task as in Experiment 1a while exposed to partial facial expressions composed of actions units (AUs) present or absent in some parts of the face (top, middle, or bottom). The coding of the AUs produced by the models showed complex facial configurations for most emotional expressions, with several AUs in common. Eye-tracking data indicated that relevant facial actions were actively gazed at by the decoders during both accurate recognition and errors. False recognition was mainly associated with the additional visual exploration of less relevant facial actions in regions containing ambiguous AUs or AUs relevant to other emotional expressions. Finally, the recognition of facial emotions from partial expressions showed that no single facial actions were necessary to effectively communicate an emotional state. In contrast, the recognition of facial emotions relied on the integration of a complex set of facial cues.

Changing Faces: Dynamic Emotional Face Processing in Autism Spectrum Disorder Across Childhood and Adulthood

BACKGROUND

Autism spectrum disorder (ASD) is classically associated with poor emotional face processing. Few studies, however, have used more ecological dynamic stimuli. We contrasted functional magnetic resonance imaging measures of dynamic emotional face processing in ASD and typically developing (TD) cohorts across a wide age range to determine if the processing and age-related trajectories differed between participants with and without ASD.

METHODS

Functional magnetic resonance imaging data collected from 200 participants (5-42 years old; 107 in ASD cohort, 93 in TD cohort) during the presentation of dynamic emotional faces (neutral-to-happy, neutral-to-angry) and dynamic flowers (closed-to-open) were analyzed. Group differences and group-by-age interactions in the faces versus flowers and between emotion contrasts were investigated.

RESULTS

Differences in activation between dynamic faces and flowers in occipital regions, including the fusiform gyri, were reduced in the ASD group. Contrasting the two emotions, ASD compared with TD participants showed increased engagement of the precentral, postcentral, and superior temporal gyri to happy faces and increased activation to angry faces occipitally. Emotion processing regions, such as insula, temporal pole, and frontal regions, showed increased recruitment with age to happy faces compared with both angry faces and flowers in the TD group, but decreased recruitment with age in the ASD group.

CONCLUSIONS

Using dynamic stimuli, we demonstrated that participants with ASD processed faces similarly to nonface stimuli, and age-related atypicalities were more pronounced to happy faces in participants with ASD. We demonstrated emotion-specific atypicalities in a large group of participants with ASD that underscore persistent difficulties from childhood into mid-adulthood.

Human-like maternal left-cradling bias in monkeys is altered by social pressure

About 66–72% of human mothers cradle their infants on their left side. Given that left-cradling exposes the baby’s face to the mother’s left visual field (i.e., mainly projected to her right hemisphere) and is altered by emotional states such as stress, maternal left-cradling was interpreted as reflecting right-hemispheric dominance for emotional processing. Whether this phenomenon is unique to human evolution is still in debate. In the present study we followed 44 olive baboon (Papio anubis) mothers and their infants in different social groups. We found that a maternal cradling bias exists and is predominantly towards the left in a similar proportion as in humans, but shifts toward a right bias in mothers living in high density groups. The sensitivity of left-cradling to social pressure highlights its potential links with the mother’s stress as reported in humans. Our finding clearly illustrates the phylogenetic continuity between humans and Old-World monkeys concerning this lateralization and its potential links with hemispheric specialization for emotions, inherited from a common ancestor 25–35 million years ago.

Carrying human infants - An evolutionary heritage

We propose that infant carrying is a biological norm for human caregiving, given that human infants have evolved a capacity to cling onto an upright caregiver whose body co-evolved to enable offspring carrying. The origins of this mutual adaptation may date back 4 million years, with the emergence of bipedalism, which precluded the infant horizontal and gravity-supported position on the back of a quadrupedal caregiver. We describe infant cooperative reflexes and behaviors, including the carrying-induced calming response and discuss hypotheses for the invention of infant carrier tools. Carrying involves several physiological and behavioral parent-infant co-adaptations that imply it is an evolutionarily conserved strategy. Epigenetic transmission of reproductive behavior through generations affects the development of the offspring, as well as the mental health of the parent. Carrying might have contributed to the evolution of Hominidae, potentially aiding dexterity, handedness, language acquisition, and social interactions. We review the evolutionary milestones and time points where the infant-caregiver interactions might have changed, exploring infant carrying as it intersects with biological and cultural evolution. We briefly summarize the effects of infant carrying on physiological, epigenetic, and socio-emotional outcomes.

Perception of Human Age from Faces: Symmetric Versus Asymmetric Movement

Dynamic movements of a face affect human perception of a person’s identification, emotional expression, speech, and so on. Findings of studies related to age perception, however, have mainly been obtained from static features of texture such as wrinkles and spots on the skin. Our goal is to investigate the perception of human age related to dynamic information. Systematically manipulated bilateral symmetric and asymmetric facial movements were utilized as stimuli in the age perception experiment. All images were low-pass filtered so that the judgment would not depend on detailed texture information. In the experiment, viewers judged the age level (the first half (indicating 20–24 and 60–64) or the latter half (indicating 25–29 and 65–69) of two age groups: 20’s and 60’s. Results revealed that faces with symmetric dynamic movements of expression (from a neutral face to one pronouncing “i”) were not only judged at the level of chance, but were also perceived to be statistically significantly younger than faces with asymmetric dynamic movements. It was also found that types of asymmetry were also effective in age perception, which might be a reflection of laterization of facial processing in a human brain.

The left-cradling bias and its relationship with empathy and depression

Women usually cradle their infants to the left of their body midline. Research showed that the left cradling could be altered by affective symptoms in mothers, so that right cradling might be associated with a reduced ability to become emotionally involved with the infant. In this study, we assessed cradling-side bias (using family photo inspection and an imagination task), as well as depression and empathy, in 50 healthy mothers of 0-3 years old children. The main finding was that the strength of the left-cradling bias was negatively related with participants' depression scores and slightly positively related with their empathy scores. Our results thus provide further evidence that cradling-side preferences can represent an evolutionary proxy of mother's affective state, influencing the early development of the infant social brain and behaviour.

Detecting Happiness Using Hyperspectral Imaging Technology

Hyperspectral imaging (HSI) technology can be used to detect human emotions based on the power of material discrimination from their faces. In this paper, HSI is used to remotely sense and distinguish blood chromophores in facial tissues and acquire an evaluation indicator (tissue oxygen saturation, StO₂) using an optical absorption model. This study explored facial analysis while people were showing spontaneous expressions of happiness during social interaction. Happiness, as a psychological emotion, has been shown to be strongly linked to other activities such as physiological reaction and facial expression. Moreover, facial expression as a communicative motor behavior likely arises from musculoskeletal anatomy, neuromuscular activity, and individual personality. This paper quantified the neuromotor movements of tissues surrounding some regions of interest (ROIs) on smiling happily. Next, we selected six regions—the forehead, eye, nose, cheek, mouth, and chin—according to a facial action coding system (FACS). Nineteen segments were subsequently partitioned from the above ROIs. The affective data (StO₂) of 23 young adults were acquired by HSI while the participants expressed emotions (calm or happy), and these were used to compare the significant differences in the variations of StO₂ between the different ROIs through repeated measures analysis of variance. Results demonstrate that happiness causes different distributions in the variations of StO₂ for the above ROIs; these are explained in depth in the article. This study establishes that facial tissue oxygen saturation is a valid and reliable physiological indicator of happiness and merits further research.