Functional lateralization in social-emotional processing: The influence of sexual orientation and gender identity on cradling preferences.

The left-cradling bias (i.e., the motor asymmetry for cradling infants on the left side) has often been associated to the right-hemispheric social-emotional specialization, and it has often been reported to be stronger in females than in males. In this study we explored the effects of sexual orientation and gender identity on this lateral bias by means of a web-based investigation in a sample of adults (485 biological females and 196 biological males) recruited through LGBTQIA+ networks and general university forums. We exploited a cradling imagery task to assess participants' cradling-side preference, and standardized questionnaires to assess participants' homosexuality (Klein Sexual Orientation Grid) and gender nonconformity (Gender Identity/Gender Dysphoria Questionnaire for Adults and Adolescents). Results confirmed the expected left-cradling bias across all sexual orientation groups except for heterosexual males. Importantly, higher homosexuality scores were associated with higher proportions of left cradling in males. These results suggest that sexual orientation can influence cradling preference in males, indicating a complex interaction between biological and psychological factors in the laterality of social-emotional processing. Finally, the left-cradling bias seems to confirm its role as a behavioral proxy of social-emotional functional lateralization in humans.

Human Lateralization, Maternal Effects and Neurodevelopmental Disorders.

In humans, behavioral laterality and hemispheric asymmetries are part of a complex biobehavioral system in which genetic factors have been repeatedly proposed as developmental determinants of both phenomena. However, no model solely based on genetic factors has proven conclusive, pushing towards the inclusion of environmental and epigenetic factors into the system. Moreover, it should be pointed out that epigenetic modulation might also account for why certain genes are expressed differently in parents and offspring. Here, we suggest the existence of a sensitive period in early postnatal development, during which the exposure to postural and motor lateral biases, expressed in interactive sensorimotor coordination with the caregiver, canalizes hemispheric lateralization in the "typical" direction. Despite newborns and infants showing their own inherent asymmetries, the canalizing effect of the interactive context owes most to adult caregivers (usually the mother), whose infant-directed lateralized behavior might have been specifically selected for as a population-level trait, functional to confer fitness to offspring. In particular, the case of the left-cradling bias (LCB; i.e., the population-level predisposition of mothers to hold their infants on the left side) represents an instance of behavioral trait exhibiting heritability along the maternal line, although no genetic investigation has been carried out so far. Recent evidence, moreover, seems to suggest that the reduction of this asymmetry is related to several unfavorable conditions, including neurodevelopmental disorders. Future studies are warranted to understand whether and how genetic and epigenetic factors affect the lateralization of early mother-infant interaction and the proneness of the offspring to neurodevelopmental disorders.

The Role of Ethnic Prejudice in the Modulation of Cradling Lateralization.

The left-cradling bias is the tendency to cradle an infant on the left side, regardless of the individuals' handedness, culture or ethnicity. Many studies revealed associations between socio-emotional variables and the left-side bias, suggesting that this asymmetry might be considered as a proxy of the emotional attunement between the cradling and the cradled individuals. In this study we examined whether adult females with high levels of prejudice toward a specific ethnic group would show reduced left-cradling preferences when required to cradle an infant-like doll with ethnical features of the prejudiced group. We manipulated the ethnicity of the cradled individual by asking 336 Caucasian women to cradle a White or a Black doll and then assessed their prejudice levels toward African individuals. Significant correlations were shown only in the Black doll group indicating that the more the prejudice toward Africans, the more the cradling-side preferences shifted toward the right. Furthermore, participants exhibiting low levels-but not those exhibiting high levels-of ethnic prejudice showed a significant left-cradling bias. These findings show that ethnic prejudice toward the specific ethnic group of the cradled individual can interfere with the left preference in the cradling woman. The present study corroborates our suggestion that the left-cradling bias might be considered as a natural index of a positive socio-communicative relationship between the cradling and cradled individuals. On the contrary, the right-cradling bias might be considered as a cue of the presence of affective dysfunctions in the relationship.

Received Cradling Bias During the First Year of Life: A Retrospective Study on Children With Typical and Atypical Development.

A population-level left cradling bias exists whereby 60-90% of mothers hold their infants on the left side. This left biased positioning appears to be mutually beneficial to both the mother and the baby's brain organization for processing of socio-emotional stimuli. Previous research connected cradling asymmetries and Autism Spectrum Disorders (ASD), entailing impairment in socio-communicative relationships and characterized by an early hypo-lateralization of brain functions. In this explorative study, we aimed to provide a contribution to the retrospective investigations by looking for early behavioral markers of neurodevelopmental disorders such as ASD. We hypothesized that an atypical trajectory in maternal cradling might be one of the possible signs of an interference in mother-infant socio-emotional communication, and thus of potential neurodevelopmental dysfunctions. To this aim, we examined photos depicting mother-child early cradling interactions by consulting family albums of 27 children later diagnosed with ASD and 63 typically developing children. As regards the first half of the first year of life, no differences were shown between maternal cradling-side preferences in typical and ASD groups, both exhibiting the left-cradling bias in the 0-3 months period, but not in the 3-6 months period. However, our results show dissimilar patterns of cradling preferences during the second half of the first year of life. In particular, the absence of left-cradling shown in typical mothers was not observed in ASD mothers, who exhibited a significant left-cradling bias in the 6-12 months age group. This difference might reflect the fact that mother-infant relationship involving children later diagnosed with ASD might remain "basic" because mothers experience a lack of social activity in such children. Alternatively, it may reflect the overstimulation in which mothers try to engage infants in response to their lack of responsiveness and social initiative. However, further investigations are needed both to distinguish between these two possibilities and to define the role of early typical and reversed cradling experiences on neurodevelopment.

The association between received maternal cradling and neurodevelopment: Is left better?

The vast majority of women (60-90%) hold infants on their left side. Such a population-level lateral bias has been shown to improve the processing of socio-emotional stimuli in both the woman and the baby. Recently, some studies related cradling lateralization and Autism Spectrum Disorders (which entail socio-communicative deficits and a reduction of the typical lateralization of brain functions), raising the possibility that the asymmetrical cradling behavior experienced during infanthood might be related to the infant's neurodevelopment. Any progress made towards earlier diagnoses could significantly increase the chance of successful intervention for these patients. We here suggest that a wide retrospective investigation on family photo albums and home movies of children diagnosed with Autism might provide useful data about early behavioral signs of this condition. We hypothesize that an atypical trajectory in maternal cradling might be one of the early signs of interference in dyadic socio-emotional communication, and thus of potential neurodevelopmental dysfunctions.

Lateralized embodiment of ambiguous human silhouettes: Data on sex differences.

Whereas the role of observers' sex has already been addressed in research on embodied cognition, so far it has been neglected as regards laterality effects in embodied cognition. Here, we report further analyses of the data used in our paper "Hemispheric asymmetries in the processing of body sides: A study with ambiguous human silhouettes" [1], where participants had to indicate the perceived orientation of silhouettes with ambiguous front/back orientation and handedness presented in the right and left hemifield. Specifically, the variables examined in the associated paper (the number of right- and left-sided silhouettes perceived as front- and back-facing in each hemifield; the number of silhouettes perceived as right- and left-handed in each hemifield) are analyzed by also factoring in participant's sex). Moreover, data are provided and analyses are performed both for the total sample of participants and for the sample of right-handed participants only. For further details, as well as for the interpretation and discussion of the data, the reader is referred to the main article [1] and its Supplementary Material.

The Relationship Between the Left-Cradling Bias and Attachment to Parents and Partner.

Mothers usually cradle their infants to the left of their body midline, an asymmetry that seems to be a typically female lateral preference. This bias is deemed to be an evolutionary facilitator of communication between cradling and cradled individuals and is believed to be strongly related to hemispheric specialization for complex socio-affective behaviors. Thus, left cradling might facilitate affective interactions in females with typical brain organization, probably due to a right-hemisphere dominance for social attachment. In this study, we investigated cradling-side preferences in 288 young females as a function of their attachment styles to parents and partners. A left-cradling bias was more frequent in participants experiencing positive relationships with their mother and romantic partners. These findings indicate that the left-cradling bias may be associated with high-quality social attachment behaviors in females and, therefore, can be considered as a natural index of socio-emotional attunement between the cradling and cradled individuals.

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.

Human mating strategies: from past causes to present consequences.

In both humans and nonhuman animals, mating strategies represent a set of evolutionary adaptations aimed at promoting individual fitness by means of reproduction with the best possible partners. Given this critical role, mating strategies influence numerous aspects of human life. In particular, between-sex divergence in the intensity of intrasexual competition could account for robust cross-cultural sex differences in psychology and behavior (e.g., personality, psychiatric disorders, social behavior, violence). Several other factors (including individual differences, relationship type and environment) affect-in an evolutionarily consistent manner-variation in mating strategy that individuals pursue (as one example, awareness of one's own attractiveness impinges on mating standards). Here we provide an overview of relevant theoretical frameworks and empirical evidence on variation in mating strategies. Given its multifaceted nature and intense research interest over several decades, this is a challenging task, and we highlight areas where further investigation is warranted in order to achieve a clearer picture and resolve apparent inconsistencies. However, we suggest that addressing outstanding questions using a variety of different methodological approaches, a deeper understanding of the cognitive representations involved in mating strategies is within reach. WIREs Cogn Sci 2018, 9:e1456. doi: 10.1002/wcs.1456 This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Neuroscience > Behavior Neuroscience > Cognition.

Hemispheric asymmetries in the processing of body sides: A study with ambiguous human silhouettes.

When required to indicate the perceived orientation of pictures of human silhouettes with ambiguous front/back orientation and handedness, both right- and left-handed participants perceive the figures more frequently as right-handed than as left-handed, which seems to indicate an attentional bias towards the right arm of human bodies. Given that past research exploiting the divided visual field paradigm indicated a processing advantage for contralateral body parts in both hemispheres, we tested whether human silhouettes with ambiguous handedness presented in the right visual field would be interpreted more frequently as right-handed compared with those presented in the left visual field. We confirmed the expected lateralised embodiment of ambiguous human bodies, in line with previous studies showing that right and left limbs are processed faster and/or more accurately when presented in the right and left hemifield, respectively.

Inversion Reveals Perceptual Asymmetries in the Configural Processing of Human Body.

Ambiguous human bodies performing unimanual/unipedal actions are perceived more frequently as right-handed/footed rather than left-handed/footed, which suggests a perceptual and attentional bias toward the right side of others' body. A bias toward the right arm of human bodies could be adaptive in social life, most social interactions occurring with right-handed individuals, and the implicit knowledge that the dominant hand of humans is usually placed on their right side might also be included in body configural information. Given that inversion disrupts configural processing for human bodies, we investigated whether inversion reduces the bias toward the right side of human bodies. Consistent with our hypothesis, when presented with ambiguous stimuli depicting humans performing lateralized actions or movements, participants perceived a greater proportion of right-handed figures when the stimuli were shown upright than when the stimuli were shown inverted. The present findings seem to confirm our hypothesis that body configural information may include some form of knowledge about the probable handedness of other individuals, although alternative accounts involving the role of experience cannot be ruled out.

Sex-specific effects of posture on the attribution of handedness to an imagined agent.

In a series of previous studies, we found that when participants were required to imagine another person performing a manual action, they imagined a significantly higher proportion of actions performed with their dominant rather than non-dominant hand, which indicates that shared motor representations between the self and the other are involved also during the imagination of others' actions. Interestingly, the activation of lateralized body-specific motor representations (as indexed by the congruence between the participant's handedness and the imagined person's handedness) appeared to be affected by the visual perspective adopted and participants' handedness. Given that past literature indicates that incongruent or unnatural postures interfere with motor imagery, we tested 480 right-handed participants to investigate whether subjects holding their right hand behind their back would have imagined right-handed actions less frequently than those holding their left hand behind their back. Moreover, we examined the effects of participant's sex, action category (simple or complex) and hand shape (open or fist). Contrary to our prediction, female participants holding their right hand behind their back imagined right-handed actions more frequently than those holding their left hand behind their back, whereas no significant effect was observed in male participants. We propose that the muscle contraction needed to keep a hand behind the back could activate the motor representations of that hand so as to increase the likelihood of imagining an action performed with the corresponding hand. Moreover, the sex difference observed is consistent with the greater use of embodied strategies by females than by males.

The influence of memory and attention on the ear advantage in dichotic listening.

The role of memory retention and attentional control on hemispheric asymmetry was investigated using a verbal dichotic listening paradigm, with the consonant-vowel syllables (/ba/,/da/,/ga/,/ka/,/pa/and/ta/), while manipulating the focus of attention and the time interval between stimulus and response. Attention was manipulated using three conditions: non-forced (NF), forced left (FL) and forced right (FR) attention. Memory involvement was varied using four delays (0, 1, 3 and 4 s) between stimulus presentation and response. Results showed a significant right ear advantage (REA) in the NF condition and an increased REA in the FR condition. A left ear advantage (LEA) was found in FL condition. The REA increased significantly in the NF attention condition at the 3-s compared to the 0-s delay and in the FR condition at the 1-s compared to the 0-s delay. No modulation of the left ear advantage was observed in the FL condition. These results are discussed in terms of an interaction between attentional processes and memory retention.

GABA levels in the ventromedial prefrontal cortex during the viewing of appetitive and disgusting food images.

Characterizing how the brain appraises the psychological dimensions of reward is one of the central topics of neuroscience. It has become clear that dopamine neurons are implicated in the transmission of both rewarding information and aversive and alerting events through two different neuronal populations involved in encoding the motivational value and the motivational salience of stimuli, respectively. Nonetheless, there is less agreement on the role of the ventromedial prefrontal cortex (vmPFC) and the related neurotransmitter release during the processing of biologically relevant stimuli. To address this issue, we employed magnetic resonance spectroscopy (MRS), a non-invasive methodology that allows detection of some metabolites in the human brain in vivo, in order to assess the role of the vmPFC in encoding stimulus value rather than stimulus salience. Specifically, we measured gamma-aminobutyric acid (GABA) and, with control purposes, Glx levels in healthy subjects during the observation of appetitive and disgusting food images. We observed a decrease of GABA and no changes in Glx concentration in the vmPFC in both conditions. Furthermore, a comparatively smaller GABA reduction during the observation of appetitive food images than during the observation of disgusting food images was positively correlated with the scores obtained to the body image concerns sub-scale of Body Uneasiness Test (BUT). These results are consistent with the idea that the vmPFC plays a crucial role in processing both rewarding and aversive stimuli, possibly by encoding stimulus salience through glutamatergic and/or noradrenergic projections to deeper mesencephalic and limbic areas.

GABA content within the ventromedial prefrontal cortex is related to trait anxiety.

The ventromedial prefrontal cortex (vmPFC) plays a key role in emotion processing and regulation. vmPFC dysfunction may lead to disinhibition of amygdala causing high anxiety levels. γ-Aminobutyric acid (GABA) inter-neurons within vmPFC shape the information flow to amygdala. Thus, we hypothesize that GABA content within vmPFC could be relevant to trait anxiety. Forty-three healthy volunteers aged between 20 and 88 years were assessed for trait anxiety with the Subscale-2 of the State-Trait-Anxiety Inventory (STAI-Y2) and were studied with proton magnetic resonance spectroscopy to investigate GABA and Glx (glutamate+glutamine) contents within vmPFC. Total creatine (tCr) was used as internal reference. Partial correlations assessed the association between metabolite levels and STAI-Y2 scores, removing the effect of possible nuisance factors including age, educational level, volumes of gray matter and white matter within magnetic resonance spectroscopy voxel. We observed a positive relationship between GABA/tCr and STAI-Y2 scores. No significant relationships were found between Glx/tCr and STAI-Y2 and between tCr/water and STAI-Y2. No differences were found between males and females as regards to age, STAI-Y2, GABA/tCr, Glx/tCr, tCr/water, gray matter and white matter volumes. We suggest a close relationship between GABA content within vmPFC and trait anxiety providing new insights in the physiology of emotional brain.

Laterality effects in the spinning dancer illusion: The viewing-from-above bias is only part of the story.

The 'silhouette illusion', representing the silhouette of a female dancer pirouetting about her vertical axis, is a bistable stimulus created by Japanese web designer Nobuyuki Kayahara. Although the dancer can be perceived as spinning either clockwise or counterclockwise, the clockwise rotation is usually preferred. Troje and McAdam (i-Perception, 2010, 1, 143) showed that this clockwise bias can be attributed to the tendency to assume a viewpoint from above rather than from below, given that the dancer is portrayed from a vantage point that is not perpendicular to the axis of rotation. Here, we tested whether another possible factor contributing to the observers' interpretation of this bistable stimulus might be the tendency to perceive movements of the right rather than the left foot. We confirmed both the viewing-from-above bias and our hypothesis. The bias to perceive movements of the right leg might be a generalization to lower limbs of a perceptual frequency effect already observed for upper limbs. Such a perceptual and attentional bias towards the right hand/foot could account for the greater ability to predict the outcome of sport actions when observing right- rather than left-limbed movements, and thus the left-handers' and left-footers' advantage observed in a variety of interactive sports.

Hearing it right: Evidence of hemispheric lateralization in auditory imagery.

An advantage of the right ear (REA) in auditory processing (especially for verbal content) has been firmly established in decades of behavioral, electrophysiological and neuroimaging research. The laterality of auditory imagery, however, has received little attention, despite its potential relevance for the understanding of auditory hallucinations and related phenomena. In Experiments 1-4 we find that right-handed participants required to imagine hearing a voice or a sound unilaterally show a strong population bias to localize the self-generated auditory image at their right ear, likely the result of left-hemispheric dominance in auditory processing. In Experiments 5-8 - by means of the same paradigm - it was also ascertained that the right-ear bias for hearing imagined voices depends just on auditory attention mechanisms, as biases due to other factors (i.e., lateralized movements) were controlled. These results, suggesting a central role of the left hemisphere in auditory imagery, demonstrate that brain asymmetries can drive strong lateral biases in mental imagery.

Upright or inverted, entire or exploded: right-hemispheric superiority in face recognition withstands multiple spatial manipulations.

Background. The ability to identify faces has been interpreted as a cerebral specialization based on the evolutionary importance of these social stimuli, and a number of studies have shown that this function is mainly lateralized in the right hemisphere. The aim of this study was to assess the right-hemispheric specialization in face recognition in unfamiliar circumstances. Methods. Using a divided visual field paradigm, we investigated hemispheric asymmetries in the matching of two subsequent faces, using two types of transformation hindering identity recognition, namely upside-down rotation and spatial "explosion" (female and male faces were fractured into parts so that their mutual spatial relations were left intact), as well as their combination. Results. We confirmed the right-hemispheric superiority in face processing. Moreover, we found a decrease of the identity recognition for more extreme "levels of explosion" and for faces presented upside-down (either as sample or target stimuli) than for faces presented upright, as well as an advantage in the matching of female compared to male faces. Discussion. We conclude that the right-hemispheric superiority for face processing is not an epiphenomenon of our expertise, because we are not often exposed to inverted and "exploded" faces, but rather a robust hemispheric lateralization. We speculate that these results could be attributable to the prevalence of right-handedness in humans and/or to early biases in social interactions.

Single-pulse Transcranial Magnetic Stimulation Reveals Contribution of Premotor Cortex to Object Shape Recognition.

BACKGROUND: It is known that ventral premotor cortex responds selectively to the visual perception of object shapes. However, it is unclear whether this activation also contributes to visual processing. OBJECTIVE: In this study we want to assess whether activation in premotor areas contributes to visual perception of objects. METHODS: We measure performance on a perception task while delivering single pulse transcranial magnetic stimulation (TMS) to the left premotor cortex at different latencies after stimulus onset. RESULTS: We show that in cases of limited visual consciousness, disturbing the left premotor cortex 150 ms after stimulus onset results in a decrease in the capacity to recognize shapes, compared both to other latencies and to stimulation of the vertex. CONCLUSION: Premotor cortex plays a constitutive role in object shape recognition.