The nature and nurture of human infant hand preference

Fifty Years of Handedness Research: A Neurological and Methodological Update

Handedness, a complex human aspect that reflects the functional lateralization of the hemispheres, also interacts with the immune system. This study aimed to expand the knowledge of the lateralization of hand, foot, and eye activities in patients with immune-mediated (IM) or other (noIM) neurological diseases and to clarify the properties of the Edinburgh Handedness Inventory (EHI) in an Italian population. Three hundred thirty-four patients with IM or noIM diseases affecting the brain or spine and peripheral nervous system were interviewed about stressful events preceding the disease, subjective handedness, and familiarity for left-handedness or ambidexterity. The patients and 40 healthy subjects underwent EHI examination. In the whole group of participants, 24 items of the EHI were classified into five factors (Hand Transitive, Hand Refined, Hand Median, Foot, Eye), demonstrating good reliability and validity. Chronological age had a significant influence on hand and foot EHI factors and the laterality quotient (LQ), particularly on writing and painting. In the patient groups, EHI factors and the LQ were also predicted by age of disease onset, duration of disease, and family history of left-handedness or ambidexterity. No differences were found between patients and healthy subjects, but pencil use scored significantly lower in patients with IM diseases than in those with noIM brain diseases. These results demonstrate that the lateralization of hand and foot activities is not a fixed human aspect, but that it can change throughout life, especially for abstract and symbolic activities. Chronic neurological diseases can cause changes in handedness. This may explain why, unlike systemic immunological diseases, IM neurological diseases are not closely associated with left-handedness. In these patients, the long version of the EHI is appropriate for determining the lateralization of body activities to contextualize the neurological picture; therefore, these findings extend the Italian normative data sets.

Assessing the Relationship Between Religious Beliefs and Ethnicity and Handedness and Footedness

Objectives The objective of the study is to explore the correlation between handedness and footedness and various demographic factors, including sex, age, faith, ethnicity, and perceived social pressures on limb use, among Muslims and non-Muslims. Methods This is an analytical cross-sectional study conducted in Saudi Arabia from September 2020 to February 2021. This research involved healthy community members aged 18 and above. An electronic survey was administered to collect demographic information on age, sex, faith, ethnicity, and the perceived degree of social pressure favoring the use of the right hand. The Waterloo handedness questionnaire (WHQ-Ar) and Waterloo footedness questionnaire (WFQ-Ar) were utilized for the assessments. Results A total of 728 respondents completed the survey. The mean (SD) age was 34.54 (11.53). Among them, 454 (62.4%) were ethnically Arab, and 507 (69.64%) identified as Muslims. The mean (SD) WHQ-Ar and WFQ-Ar scores were 42 (31.6) and 10.51 (8.1), respectively, with higher scores indicating "right" preference. Older age was associated with higher scores (p = 0.01) and men with lower handedness scores (p = 0.003). Participants who did not perceive social pressure had significantly lower scores (p < 0.001). Footedness was associated with slightly lower scores in Muslims (p = 0.001). Conclusion The degree of pressure perceived to use a particular hand has a major influence on handedness scores in Muslims and non-Muslims alike; this was true even when comparing populations with different levels of permissiveness to specific hand use due to varying religious or cultural backgrounds. Social pressure, regardless of routine religious practices, is more likely to influence handedness scores. Age and sex influence the scores similar to international reports, and footedness appears less likely to fall under the influence of cultural pressures.

Influence of target location, task complexity, and gender on children's use of their preferred foot

The goal of the present study was to compare the choice of foot of right-footed children with varying strengths of foot preference when performing two tasks of different levels of complexity at three spatial locations. 30 right-footed children were tested. The results showed that the general tendency to use one's preferred foot to interact with an object is more or less pronounced depending on the object's location and the complexity of the task. The children used their non-preferred left foot more often during the simple task and when the object was presented to the left. Our findings also revealed interactions between gender, age, and spatial location. At five, girls used globally less their left foot than boys. In addition, girls used their preferred right foot more frequently than boys when the object was presented to the left. Based on these results, it can be concluded that foot selection depends on foot preference, task demand, environmental context, and biological factors associated with motor dominance.

The development of hand, foot, trunk, hearing, and visual lateral preference throughout the lifespan

This research investigated the developmental process of five lateral preference dimensions (hand, foot, trunk, hearing, and visual preference). A total of 1236 volunteers participated in this study, divided into five age groups: 07-12 (n = 247); 13-17 (n = 234); 18-30 (n = 227); 31-60 (n = 225); and 61-90 years old (n = 303). Lateral preference was assessed via questionnaire with the Global Lateral Preference Inventory. By assessing the degree and direction of lateral preference in different ages, our results revealed a pattern of lateralization strengthening with aging in all the analyzed dimensions. We also verified significant correlation between hand preference and the other dimensions for all age groups, but correlation was stronger in the 7-12 group for all correlation pairs. Our results lead to the suggestion of an underlying general lateralization process in early ages (7-12 years old) followed by specific developmental trajectories of each preference dimension (13 years forward), likely startled by hemisphere and functional specialization related to innate developmental patterns of neural structures and social/environmental influences.

Broca area homologue's asymmetry reflects gestural communication lateralisation in monkeys (Papio anubis)

Manual gestures and speech recruit a common neural network, involving Broca’s area in the left hemisphere. Such speech-gesture integration gave rise to theories on the critical role of manual gesturing in the origin of language. Within this evolutionary framework, research on gestural communication in our closer primate relatives has received renewed attention for investigating its potential language-like features. Here, using in vivo anatomical MRI in 50 baboons, we found that communicative gesturing is related to Broca homologue’s marker in monkeys, namely the ventral portion of the Inferior Arcuate sulcus (IA sulcus). In fact, both direction and degree of gestural communication’s handedness – but not handedness for object manipulation are associated and correlated with contralateral depth asymmetry at this exact IA sulcus portion. In other words, baboons that prefer to communicate with their right hand have a deeper left-than-right IA sulcus, than those preferring to communicate with their left hand and vice versa. Interestingly, in contrast to handedness for object manipulation, gestural communication’s lateralisation is not associated to the Central sulcus depth asymmetry, suggesting a double dissociation of handedness’ types between manipulative action and gestural communication. It is thus not excluded that this specific gestural lateralisation signature within the baboons’ frontal cortex might reflect a phylogenetical continuity with language-related Broca lateralisation in humans.

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.

Maternal cradling bias in baboons: The first environmental factor affecting early infant handedness development?

The most emblematic behavioral manifestation of human brain asymmetries is handedness. While the precise mechanisms behind the development of handedness are still widely debated, empirical evidences highlight that besides genetic factors, environmental factors may play a crucial role. As one of these factors, maternal cradling behavior may play a key role in the emergence of early handedness in the offspring. In the present study we followed 41 Papio anubis infants living in social groups with their mother for which direction (e.g., left- or right-arm) and degree of maternal cradling-side bias were available from a previous published study. We assessed hand preferences for an unimanual grasping task at three developmental stages: (A) 0-4, (B) 4-6, and (C) 9-10 months of age. We found that individual hand preferences for grasping exist as soon as the first months of age, with a population-level left-handedness predominance, being stable until 6 months; to wit the period during which juveniles are mainly carried by their mothers. More importantly, this early postnatal handedness is positively correlated with maternal cradling lateralization. Interestingly, hand preferences assessed later in the development, once juveniles are no longer carried (i.e., from 9 to 10 months of age), are less dependent from the maternal cradling bias and less consistent with the earlier developmental stages, especially in infants initially cradled on the right maternal side. Our findings suggest that the ontogenetic dynamics of the infant's hand preference and its changes might ultimately rely on the degree of infant dependence from the mother across development.

It Is Not Just in the Genes

Asymmetries in the functional and structural organization of the nervous system are widespread in the animal kingdom and especially characterize the human brain. Although there is little doubt that asymmetries arise through genetic and nongenetic factors, an overarching model to explain the development of functional lateralization patterns is still lacking. Current genetic psychology collects data on genes relevant to brain lateralizations, while animal research provides information on the cellular mechanisms mediating the effects of not only genetic but also environmental factors. This review combines data from human and animal research (especially on birds) and outlines a multi-level model for asymmetry formation. The relative impact of genetic and nongenetic factors varies between different developmental phases and neuronal structures. The basic lateralized organization of a brain is already established through genetically controlled embryonic events. During ongoing development, hemispheric specialization increases for specific functions and subsystems interact to shape the final functional organization of a brain. In particular, these developmental steps are influenced by environmental experiences, which regulate the fine-tuning of neural networks via processes that are referred to as ontogenetic plasticity. The plastic potential of the nervous system could be decisive for the evolutionary success of lateralized brains.

Is Handedness at Five Associated with Prenatal Factors?

The goal of the study was to investigate some of the factors suspected to be related to children's handedness: presentation during the last weeks of gestation and at birth (cephalic or breech), side of presentation (right or left), number of weeks of gestation, season of birth, parents' handedness and sex. We analyzed the relationships between these factors and the child's handedness at five years. Children (n = 1897) from the EDEN cohort participated in the study, among which 1129 were tested for handedness at five. The father's handedness, but not the mother's, was significantly related to the child's hand preference. The percentage of left-handed children was significantly larger when the father was non-right-handed compared to right-handed, and tended to be larger among children in non-left-cephalic presentation compared to left-cephalic presentation. Girls, but not boys, were significantly less lateralized when they were born before 37 weeks of pregnancy than after. Finally, children born in winter or spring were slightly but significantly less lateralized than children born in summer or autumn. All six children who were not lateralized at 5 presented one or several of these factors. These results are discussed in light of the mixed model of handedness.

Are the Predictions of the Dynamic Dominance Model of Laterality Applicable to Children?

According to the dynamic dominance model, the left cerebral hemisphere is specialized for the control of intersegmental dynamics and the right hemisphere for impedance control. Our aim was to test predictions from the dynamic dominance model in children by comparing performance between the right (preferred) and left hands in aiming. Three groups were compared: 4-7, 8-11, and 18-38 years old. Results showed higher movement linearity in the performance with the right hand in all age groups (P < .01), while initial directional error and endpoint accuracy were equivalent between hands. These results provided partial support for the dynamic dominance model.

Laterality in Children: Evidence for Task-Dependent Lateralization of Motor Functions

The behavioral preference for the use of one side of the body starts from pre-natal life and prompt humans to develop motor asymmetries. The type of motor task completed influences those functional asymmetries. However, there is no real consensus on the occurrence of handedness during developmental ages. Therefore, we aimed to determine which motor asymmetries emerged differently during childhood. A total sample of 381 children in grades 1 to 5 (6-11 years old) of primary school were recruited and tested for two fine coordination tasks (Floppy, led by dexterity, and Thumb, led by speed-dominated skills) and handgrip strength (HS). Data about their handedness, footedness and sports participation were also collected. Children performed better with their dominant side, especially for the Floppy and HS tests. The asymmetries were more marked in right-handed children and did not differ by age, gender or type of sport. Our findings support the thesis of a functional lateralization in complex coordinative tasks and in maximal strength during developmental ages. Furthermore, our findings extend the evidence of a stronger lateralization in right-handed individuals, demonstrating it at a functional level in primary school children performing motor tasks. Fine motor skills allow a "fine" understanding of developmental trajectories of lateralized behavior.

The Human Face Becomes Mapped as a Sensorimotor Reaching Space During the First Year

Although recent behavioral and neural research indicates that infants represent the body's structure, how they engage self-representations for action is little understood. This study addressed how the human face becomes a reaching space. Infants (N = 24; 2-11 months) were tested longitudinally approximately every 3 weeks on their ability to reach to a vibrating target placed at different locations on the face. Successful reaches required coordinating skin- and body-based codes for location, a problem known as tactile remapping. Findings suggest that a functional representation of the face is initially fragmented. Infants localized targets in the perioral region before other areas (ears/temples). Additionally, infants predominantly reached ipsilaterally to targets. Collectively, the findings illuminate how the face becomes an integrated sensorimotor space for self-reaching.

Human laterality for manipulation and gestural communication: A study of beach-volleyball players during the Olympic Games

Comparative studies can help understand better brain functional lateralization for manipulation and language. This study investigated and compared, for the first time, human adults' laterality for manipulation and gestures in a non-experimental social context. We analysed the manual laterality of 48 beach volleyball athletes for four frequently expressed behaviours: a complex throwing action (jump serve) and three gestures (CLAP HAND, PUMP FIST and SLAP HAND-TO-HAND). We evaluated population-level laterality bias for each of the four behaviours separately, compared manual laterality between behaviours and investigated factors influencing gestural laterality. We furthered our between-gestures comparison by taking into account three categories of factors simultaneously: gesture characteristics (sensory modality), interactional context components (positions of interactants and emotional valence), and individual demographic characteristics (age, sex and country). Our study showed that (1) each behaviour considered presented a population-level right-hand bias, (2) differences of laterality between behaviours were probably related to gesture sensory modality and (3) signaller's laterality was modulated differently in relation to positions of interactants, emotional valence, age and sex. Our results support the literature suggesting that left-hemisphere specialization for manipulation and language (speech and gestures) may have evolved from complex manual activities such as throwing and from gestural communication.

Adult attachment style and lateral preferences in physical proximity

Attachment scale is constructed from two components (anxiety and avoidance) effectively treated as providing salient measures in previous studies. Recent studies have suggested associations between sensitivities to physical warmth and anxiety scores of attachment scale. Some researchers also suggest that the degree of one's comfort with physical proximity depends on attachment styles, attributing differences to the number of oxytocin (a neuropeptide released by physical touch) receptors. Lateral preference is an important aspect of physical proximity, coupled with the lateralization of visual, emotional, and other cognitive systems. However, there are few studies investigating the relationship between attachment scale scores and one's lateral preferences in physical proximity. Here we surveyed the preferences of subjects regarding positional relations with their romantic partner in some daily situations, and examined the association with attachment scale score. Our results show that the existence or absence of partner correlates with different relations between attachment styles and subjects' awareness of lateral preferences. Lateral preferences in physical proximity may play an important role in attachment in adulthood.

A historical, systematic review of handedness origins

Handedness ontogenesis is still under debate in science. This systematic review analyzed articles regarding the theories and basis of handedness formation, highlighting the historical knowledge path that this literature underwent. Cochrane Library, LILACS, Web of Sciences, Science Direct and PubMed databases were searched. This review included review studies with handedness as the main topic. Only papers written in English with analyses exclusively in neurotypical humans (any age range) were included. Different approaches (genetic, neural, social, and behavioural) were reviewed in light of growing evidence, summarizing the current state of the art. Genetic and environmental/social impacts are common points in most of the reviews, each given more or less importance, depending on the author and theory proposed. Multifactorial, developmental approaches to handedness formation seem to be the most up to date view of the phenomenon. Different control mechanisms between hemisphere and neural asymmetries are also contributing factors to handedness formation.

Cognitive-perceptual load modulates hand selection in left-handers to a greater extent than in right-handers

Previous studies have proposed that selecting which hand to use for a reaching task appears to be modulated by a factor described as "task difficulty," defined by either the requirement for spatial precision or movement sequences. However, we previously reported that analysis of the movement costs associated with even simple movements plays a major role in hand selection. We further demonstrated, in right-handers, that cognitive-perceptual loading modulates hand selection by interfering with the analysis of such costs. It has been reported that left-handers tend to show less dominant hand bias in selecting which hand to use during reaching. We, therefore, hypothesized that hand selection would be less affected by cognitive-perceptual loading in left-handers than in right-handers. We employed a visual search task that presented different levels of difficulty (cognitive-perceptual load), as established in previous studies. Our findings indicate that left-handed participants tend to show greater modulation of hand selection by cognitive-perceptual loading than right-handers. Left-handers showed lower dominant hand reaction times than right-handers, and greater high-cost movements that reached to extremes of the contralateral workspace under the most difficult task conditions. We previously showed in this task that midline crossing has high-energy and time costs and that they occur more frequently under cognitively demanding conditions. The current study revealed that midline crossing was associated with the lowest reaction times, in both handedness groups. The fact that left-handers showed lower dominant hand reaction times, and a greater number of high-cost cross-midline reaches under the most cognitively demanding conditions suggests that these actions were erroneous.

The home handedness questionnaire: pilot data from preschoolers

While handedness questionnaires are widely used in adults, there is no comparable measure designed specifically for children. The current study developed the Home Handedness Questionnaire (HHQ), a new measure for preschoolers administered by parents using common household items. The HHQ has two scales that distinguish action types typically combined on other measures: actions performed with only the right or left hand (i.e., unimanual, such as holding a toothbrush), and actions performed with one hand holding the object for the other hand's action (i.e., role-differentiated bimanual manipulation or RDBM, such as unscrewing a lid from a jar). The HHQ was able to detect right preference, left preference, and no preference for unimanual and RDBM actions in a proof of concept study in 3-year-olds (N = 64). The HHQ identified a majority of children as right-handed, but was also sensitive to variability in direction across skill types. Approximately one-quarter of children in the sample had mixed preferences for the two types of manual skills, suggesting that for a subgroup of children, hand use patterns may still be undergoing change. Suggestions for refining the HHQ are discussed. Overall, the HHQ is a promising multidimensional parent-led tool for assessing preschool handedness.

Prevalence and characteristics of positional plagiocephaly in healthy full-term infants at 8-12 weeks of life

Positional plagiocephaly (PP) denotes flattening of the skull that occurs frequently in healthy infants. Aim of this study was to estimate the prevalence of positional plagiocephaly and to identify the risk factors in a cohort of healthy infants in order to help prevention of PP. In a prospective design, all healthy full-term infants, ranging from 8 to 12 weeks of age, who presented at the public immunization clinic in Ferrara, were eligible for the study. After obtaining informed consent, we interviewed the parents and examined the infants using the Argenta's assessment tool. Of 283 infants examined, 107 (37.8%) were found to have PP at 8-12 weeks of age. In 64.5%, PP was on the right side, 50.5% were male and 15% presented also with brachycephaly. Risk factors significantly associated were lower head circumference, advanced maternal age, Italian compared to African, and supine sleep position, in particular for infants born at 37 weeks, preference for one side of the head. In logistic regression, risk factors significantly associated were lower birth weight, advanced maternal age, and supine sleep position.

CONCLUSIONS

Positional plagiocephaly is a common issue faced by pediatricians; our results reinforce the need of improving prevention both of sudden infant death and positional plagiocephaly, through uniform messages provided prenatally and postnatally by different health professionals. "What is Known:" •The incidence of positional plagiocephaly varies due to population studied and measuring methods. •Different factors are considered in the literature as being associated to positional plagiocephaly (infant factors, obstetric factors, infant care practices, sociodemographic factors). "What is New:" •This is one of the few European studies quantifying positional plagiocephaly prevalence in a population of unselected healthy infants. •In this study, positional plagiocephaly is confirmed as a common issue, related to some factor (as supine sleep position and positional head prevalence) that should be addressed in pre and postnatal counseling. •The prone sleepers rate in our population highlight the need to improve parental awareness regarding SIDS prevention, in particular in borderline gestational age.

Beyond handedness: assessing younger adults and older people lateral preference in six laterality dimensions

Lateral preference is influenced by many different factors. Although studies that assessed handedness contributed greatly to our understanding of the phenomenon, looking to other dimensions of motor laterality, such as lower limbs, trunk, visual and hearing preference, may be an interesting strategy to further advance in the field. Comparing different age groups with a complete inventory also contributes to understanding the ageing impact on these variables. Our aim, therefore, was to assess six motor laterality dimensions in younger adults and older people. Two hundred subjects participated in this study (102 adults, 30.6 ± 11.2 years old, and 98 elders, 70.4 ± 7.22 years old) and lateral preference was assessed by the Global Lateral Preference Inventory. We verified significant differences between groups in all dimensions, except the visual one, with proportionally stronger right preference in the older group. Compared to other dimensions, higher frequency of ambidexterity was observed in trunk, hearing and visual preference for both groups. These results might indicate that lateral preference is, indeed, multifactorial, being affected by ageing, task complexity and other possible related aspects.

Effect of optic flows on newborn crawling

This study examined the crawling characteristics of newborns placed prone on a water-filled, transparent pediatric mattress and whether exposure to terrestrial optic flows that specify forward and backward displacement would influence leg and arm crawling movements. Twenty-six 3-day-old newborns were exposed to a static checkerboard pattern that was back-projected onto the surface underneath the mattress or a checkerboard pattern that moved toward or away from them at 0.12 m/s. Significantly more flexion and extension crawling movements of the legs were observed in the optic flow conditions, although infants did not displace their bodies significantly further on the mattress in these conditions. Unique aspects of newborn crawling were also identified.

The origin of human handedness and its role in pre-birth motor control

The vast majority of humans are right-handed, but how and when this bias emerges during human ontogenesis is still unclear. We propose an approach that explains postnatal handedness starting from 18 gestational weeks using a kinematic analysis of different fetal arm movements recorded during ultrasonography. Based on the hand dominance reported postnatally at age 9, the fetuses were classified as right-handed (86%) or left-handed, in line with population data. We revealed that both right-handed and left-handed fetuses were faster to reach to targets requiring greater precision (i.e., eye and mouth), with their dominant (vs. non-dominant) hand. By using either movement times or deceleration estimates, handedness can be inferred with a classification accuracy ranging from 89 to 100% from gestational week 18. The reliability of this inference hints to the yet unexplored potential of standard ultrasonography to advance our understanding of prenatal life.

Captive gorillas' manual laterality: The impact of gestures, manipulators and interaction specificity

Relationships between humans' manual laterality in non-communicative and communicative functions are still poorly understood. Recently, studies showed that chimpanzees' manual laterality is influenced by functional, interactional and individual factors and their mutual intertwinement. However, what about manual laterality in species living in stable social groups? We tackled this question by studying three groups of captive gorillas (N=35) and analysed their most frequent manual signals: three manipulators and 16 gesture types. Our multifactorial investigation showed that conspecific-directed gestures were overall more right-lateralized than conspecific-directed manipulators. Furthermore, it revealed a difference between conspecific- and human-directed gestural laterality for signallers living in one of the study groups. Our results support the hypothesis that gestural laterality is a relevant marker of language left-brain specialisation. We suggest that components of communication and of manipulation (not only of an object but also of a conspecific) do not share the same lateralised cerebral system in some primate species.

Emerging Trends in the Multimodal Nature of Cognition: Touch and Handedness

Advances in tactile cognition and haptics have increased our understanding of the multimodal nature of touch. Haptic data is mostly confined to human performance arising from the flexibility and dexterity of the fingers used to discriminate shapes and objects. Studies with infants indicate that recognition of objects either seen or held in the hand is possible during early periods of infancy. Evidence indicates performance differences between the hands decrease over periods of development, reflecting maturation of the cortical brain system supporting motor skills. Thus ability is not confined to the preferred hand. Tactile process and haptic cognition reflect hand ability. Studies examining manual performance must consider the relevance of haptics in research. Knowing about the evolution of the hands controlled by the cerebral hemispheres is of interest because it is a major contribution to the repertoire of human hand actions. The emergence of RDBM (role differentiated bimanual manipulation) is an important shift in the development of infant manual skills. Between 4 and 7 months of age, infants begin to manipulate objects using RDBM where one hand stabilized an object while the other hand manipulated the object. Understanding the affordance of a tool is an important cognitive milestone in early sensorimotor period that develops during the second year in full-term infants. This ability has also been demonstrated in preterm infants indicating the emergence of handedness during prenatal periods. Thus a multimodal approach that incorporates studies of tactile processes and hand actions may reveal their interactions with task demands and haptic ability.

Difference in Cortical Relay Time Between Intrinsic Muscles of Dominant and Nondominant Hands

The authors aimed to calculate and compare cortical relay time (CRT) between intrinsic hand muscles and between homonymous muscles of dominant and nondominant hands. The participants comprised 22 healthy volunteers. The CRT for long-latency reflexes (LLRs) was calculated by subtracting the peak latency of somatosensory evoked potentials of component N20 and the onset latency of motor evoked potentials from the onset latency of LLRs. CRT was significantly shorter for the first dorsal interosseous muscle than for the abductor pollicis brevis muscle, regardless of hand dominance. CRT for the abductor pollicis brevis muscle was significantly shorter in the dominant hand than in the nondominant hand. Evaluation of CRT for intrinsic muscles might be beneficial in the understanding of individuated finger functions.

The Role of Visual and Haptic Feedback During Dynamically Coupled Bimanual Manipulation

The mechanisms that underlie the control of bimanual actions in which the two hands act separately to manipulate different objects (uncoupled independent control) has been well studied. In contrast, much less is known about how the central nervous system controls bimanual actions that require the two hands act cooperatively to manipulate a single object (dynamically coupled control). Furthermore, there is scant research into the manual lateralization and role assignment in the processing of visual and haptic feedback during dynamically coupled bimanual tasks. In this experiment, we examined the role of the dominant and non-dominant hands during a dynamically coupled bimanual task in which visual and haptic feedback regarding object penetration were manipulated. Twelve subjects performed a bimanual grasp and reach task towards different target locations in the workspace by using two identical wrist robotic devices. Results showed haptic feedback is necessary for task completion, and that hand specialization plays a fundamental role in spatial and temporal coordination between the two limbs.

Clinical assessment of head orientation profile development and its relationship with positional plagiocephaly in healthy term infants - A prospective study

BACKGROUND

Positional plagiocephaly refers to atypical development of an uneven head shape with asymmetrical head orientation as a post-natal risk factor. The development of the head orientation profile and its relationship with positional plagiocephaly are lacking.

OBJECTIVES

To explore the head orientation profile development and its relationship with positional plagiocephaly in healthy full term infants.

METHODS

A prospective observational study including 94 infants was conducted. Head orientation measures including head orientation duration, head orientation strength and latency to turn were conducted at three, six and nine weeks of age. Plagiocephaly outcome was measured by modified Cranial Vault Asymmetry Index at nine weeks.

RESULTS

Lateral head orientation duration predominated at three weeks, mean (standard deviation) (right=40 [21.7]%; left=41 [21.5]%; midline=19 [19.9]%). It decreased bilaterally in favour of midline positioning at nine weeks (right=30 [22.3]%; left=24 [22.0]%; midline=46 [27]%. Although head orientation strength was similar across the three ages after accounting for side, head orientation strength to left was decreased from three to nine weeks (p=0.031; 95% CI: 0.12-2.06). There was a reduction in left-consistent with increase in left-bias from 3weeks to 6weeks of age (p=0.011). Positional plagiocephaly at nine weeks was associated with head orientation duration-right (p<0.001; r(2)=0.20); head orientation duration-left (p<0.001; r(2)=0.17); head orientation strength at three and six weeks (p<0.001; r(2)=0.22), but not latency to turn.

CONCLUSIONS

Healthy infants show progressive change from symmetrical lateral head orientation to midline orientation from three to nine weeks. There is association of head orientation duration and strength with positional plagiocephaly.

Defining the nature and implications of head turn preference in the preterm infant

AIM

To determine the relationship of head turn preference in the preterm infant to: 1) perinatal medical factors, 2) neonatal neurobehavior, and/or 3) infant neurodevelopmental outcomes.

METHODS

Seventy preterm infants born ≤30weeks gestation were enrolled at birth. Detailed information regarding neonatal intensive care unit (NICU) medical course was compiled for each infant. Neurobehavioral testing was performed during NICU hospitalization. Head turn preference was quantified at term equivalent age using a newly developed scale. Infants returned at age two years for standardized developmental testing.

RESULTS

All infants demonstrated a head turning preference, with most preferring the right side (n=51, 77%). Fifty-five infants (79%) had moderate to severe head turn preference. Head turn preference was associated with 1) medical severity (hours of inotrope use, p=0.02; oxygen requirement at 36weeks postmenstrual age, p=0.03), 2) worse neurobehavioral performance (decreased self-regulation, p=0.007; more sub-optimal reflexes p=0.006), and 3) worse developmental outcome at age two years (poorer fine motor, p=0.02).

INTERPRETATION

Medical factors in the NICU appear to be associated with the development of a head turn preference. Increased severity of head turn preference may be a marker for poor developmental outcome. Early identification may inform therapeutic interventions designed to minimize symptoms and optimize neurodevelopmental outcome.

The contributions of vision and haptics to reaching and grasping

This review aims to provide a comprehensive outlook on the sensory (visual and haptic) contributions to reaching and grasping. The focus is on studies in developing children, normal, and neuropsychological populations, and in sensory-deprived individuals. Studies have suggested a right-hand/left-hemisphere specialization for visually guided grasping and a left-hand/right-hemisphere specialization for haptically guided object recognition. This poses the interesting possibility that when vision is not available and grasping relies heavily on the haptic system, there is an advantage to use the left hand. We review the evidence for this possibility and dissect the unique contributions of the visual and haptic systems to grasping. We ultimately discuss how the integration of these two sensory modalities shape hand preference.

Increased cortical thickness and altered functional connectivity of the right superior temporal gyrus in left-handers

Altered structure in the temporal cortex has been implicated in the variable language laterality of left-handers (LH). The neuroanatomy of language lateralization and the corresponding synchronous functional connectivity (FC) in handedness cohorts are not, however, fully understood. We used structural and resting-state functional magnetic resonance imaging (fMRI) data to investigate the effect of altered cortical thickness on FC in LH and right-handers (RH). Whole-brain cortical thickness was calculated and compared between the LH and RH. We observed increased cortical thickness in the right superior temporal gyrus (STG) in the LH. A further FC analysis was conducted between the right STG and the remaining voxels in the brain. Compared with RH, the LH showed significantly higher FC in the left STG, right occipital cortex, and lower FC in the left inferior frontal gyrus and supramarginal gyrus. Our findings suggest that LH have atypical connectivity in the language network, with an enhanced role of the STG, findings which provide novel insights into the structural and functional substrates underlying the atypical language development of left-handed individuals.

Handedness and effective connectivity of the motor system

Handedness denotes the individual predisposition to consistently use the left or right hand for most types of skilled movements. A putative neurobiological mechanism for handedness consists in hemisphere-specific differences in network dynamics that govern unimanual movements. We, therefore, used functional magnetic resonance imaging and dynamic causal modeling to investigate effective connectivity between key motor areas during fist closures of the dominant or non-dominant hand performed by 18 right- and 18 left-handers. Handedness was assessed employing the Edinburgh-Handedness-Inventory (EHI). The network of interest consisted of key motor regions in both hemispheres including the primary motor cortex (M1), supplementary motor area (SMA), ventral premotor cortex (PMv), motor putamen (Put) and motor cerebellum (Cb). The connectivity analysis revealed that in right-handed subjects movements of the dominant hand were associated with significantly stronger coupling of contralateral (left, i.e., dominant) SMA with ipsilateral SMA, ipsilateral PMv, contralateral motor putamen and contralateral M1 compared to equivalent connections in left-handers. The degree of handedness as indexed by the individual EHI scores also correlated with coupling parameters of these connections. In contrast, we found no differences between right- and left-handers when testing for the effect of movement speed on effective connectivity. In conclusion, the data show that handedness is associated with differences in effective connectivity within the human motor network with a prominent role of SMA in right-handers. Left-handers featured less asymmetry in effective connectivity implying different hemispheric mechanisms underlying hand motor control compared to right-handers.

Effect of handedness on the occurrence of semantic N400 priming effect in 18- and 24-month-old children

It is frequently stated that right-handedness reflects hemispheric dominance for language. Indeed, most right-handers process phonological aspects of language with the left hemisphere (and other aspects with the right hemisphere). However, given the overwhelming majority of right-handers and of individuals showing left-hemisphere language dominance, there is a high probability to be right-handed and at the same time process phonology within the left hemisphere even if there was no causal link between both. One way to understand the link between handedness and language lateralization is to observe how they co-develop. In this study, we investigated to what extent handedness is related to the occurrence of a right-hemisphere lateralized N400 event related potential in a semantic priming task in children. The N400 component in a semantic priming task is more negative for unrelated than for related word pairs. We have shown earlier that N400 effect occurred in 24-month-olds over the right parietal-occipital recording sites, whereas no significant effect was obtained over the left hemisphere sites. In 18-month-olds, this effect was observed only in those children with higher word production ability. Since handedness has also been associated with the vocabulary size at these ages, we investigated the relationship between the N400 and handedness in 18- and 24-months as a function of their vocabulary. The results showed that right-handers had significantly higher vocabulary size and more pronounced N400 effect over the right hemisphere than non-lateralized children, but only in the 18-month-old group. We propose that the emergences of right-handedness and right-distributed N400 effect are not causally related, but that both developmental processes reflect a general tendency to recruit the hemispheres in a lateralized manner. The lack of this relationship at 24 months further suggests that there is no direct causal relation between handedness and language lateralization.