Agenesis of the corpus callosum and the establishment of handedness

Biological and environmental factors may affect children's executive function through motor and sensorimotor development: Preterm birth and cerebral palsy

Disruptive biological and environmental factors may undermine the development of children's motor and sensorimotor skills. Since the development of cognitive skills, including executive function, is grounded in early motor and sensorimotor experiences, early delays or impairments in motor and sensorimotor processing often trigger dynamic developmental cascades that lead to suboptimal executive function outcomes. The purpose of this perspective paper is to link early differences in motor/sensorimotor processing to the development of executive function in children born preterm or with cerebral palsy. Uncovering such links in clinical populations would improve our understanding of developmental pathways and key motor and sensorimotor skills that are antecedent and foundational for the development of executive function. This knowledge will allow the refinement of early interventions targeting motor and sensorimotor skills with the goal of proactively improving executive function outcomes in at-risk populations.

From Hemispheric Asymmetry through Sensorimotor Experiences to Cognitive Outcomes in Children with Cerebral Palsy

Recent neuroimaging studies allowed us to explore abnormal brain structures and interhemispheric connectivity in children with cerebral palsy (CP). Behavioral researchers have long reported that children with CP exhibit suboptimal performance in different cognitive domains (e.g., receptive and expressive language skills, reading, mental imagery, spatial processing, subitizing, math, and executive functions). However, there has been very limited cross-domain research involving these two areas of scientific inquiry. To stimulate such research, this perspective paper proposes some possible neurological mechanisms involved in the cognitive delays and impairments in children with CP. Additionally, the paper examines the ways motor and sensorimotor experience during the development of these neural substrates could enable more optimal development for children with CP. Understanding these developmental mechanisms could guide more effective interventions to promote the development of both sensorimotor and cognitive skills in children with CP.

Measuring infant handedness reliably from reaching: A systematic review

Researchers have utilized reaching paradigms to measure infant handedness for more than a century. However, methods vary widely. Recent research has identified that the number of trials used in assessment is critical with the recommendation that at least 15 trials are necessary to reliably classify infants into handedness categories via statistical cutoffs. As a first step towards establishing best practices for the field, we identified, categorized, and synthesized findings according to trial number from studies that utilized reaching to index handedness in infants across the first two years of life using PRISMA guidelines. Database searches were conducted in PsycINFO, PubMed, and Ovid MEDLINE®. All articles published through May 2018 were included. Additional records were identified through other sources. After removing duplicates, 1,116 records were screened using the online software program Abstrackr. Of these records, 125 full-text articles were further assessed for eligibility, and 87 articles were included in the qualitative synthesis. Results revealed that the majority of papers published since 1890 (70%) do not meet the 15-trial minimum criterion for statistically reliable measurement of infant handedness. Broad themes from articles meeting the measurement criterion and implications for future research are discussed.

A perspective on the development of hemispheric specialization, infant handedness, and cerebral palsy

Cerebral Palsy (CP), a common form of neurological pediatric disability, results from pre- or perinatal brain injury. Although there is growing evidence of the efficacy of motor learning-based therapies, several factors interact to produce variability in impairment and limit the effectiveness of these therapies. The variability of hand function present in children with CP indicates that a range of developmental pathways must contribute to the manifestation of individually unique characteristics of impairment. Despite two decades of progress using therapies derived from understanding the mechanisms controlling hand function, very little is known about the sensorimotor experiences occurring during development that likely shape later functional problems for children with CP. In this "perspective" paper, we propose that the study of the development of motor skills in typically developing infants may reveal experiential factors potentially important for creating remedial therapies for children with CP. Specifically, we use the development of infant handedness, a model of hemispheric specialization of function, as an example of how self-generated experiences and sensorimotor feedback can shape the development of limb control and hemispheric specialization. We illustrate how early sensorimotor asymmetries concatenate into pronounced differences in skill between the two hands. We suggest that this model of infant handedness provides a framework for studying the individual differences manifested in children with CP. These differences likely arise from aberrant sensorimotor experiences created by sensorimotor circuits disrupted by the early brain injury. We conclude that knowledge of the developmental events, including subtle motor behaviors, that shape sensorimotor pathways, can improve treatment options for children with CP.

Specialization of the motor system in infancy: from broad tuning to selectively specialized purposeful actions

In executing purposeful actions, adults select sufficient and necessary limbs. But infants often move goal-irrelevant limbs, suggesting a developmental process of motor specialization. Two experiments with 9- and 12-month-olds revealed gradual decreases in extraneous movements in non-acting limbs during unimanual actions. In Experiment 1, 9-month-olds produced more extraneous movements in the non-acting hand/arm and feet/legs than 12-month-olds. In Experiment 2, analysis of the spatiotemporal dynamics of infants' movements revealed developmental declines in the spatiotemporal coupling of movements between acting and non-acting arms. We also showed that the degree of specialization in infants' unimanual actions is associated with individual differences in motor experience and visual attention, indicating the experience-dependent and broad functional nature of these developmental changes. Our study provides important new insights into motor development: as in cognitive domains, motor behaviours are initially broadly tuned to their goal, becoming progressively specialized during the first year of life.

Visuo-manual coordination in preterm infants without neurological impairments

The extent of and reasons for visuo-manual coordination deficits in moderate and late preterm born infants without neurological impairments are not well known. This paper presents a longitudinal study on the visuo-manual development of twelve preterm infants, born after 33-36 weeks of gestation without neurological complications, between the ages of 6 and 12 months. Visuo-manual integration and grasping were assessed using the Peabody Developmental Motor Scales, along with bimanual coordination and handedness tests. Visual function was examined once prior to the beginning of the study. Gross motor development was also evaluated every month. Preterm infants were compared to a control group of ten full-term infants according to corrected age. Compared to full-terms, the visual perception of preterm infants was close to normal, with only a measure of visual fixation lower than in full-terms. In contrast, preterm infants had delayed development of visuo-manual integration, grasping, bimanual coordination, and handedness even when compared using corrected age. Tonicity and gestational age at birth were the main variables associated to the delays. These results are discussed in terms of the possible factors underlying such delays. They need to be confirmed on a larger sample of preterm born children, and to be correlated with later development. This would allow developing markers of future neuropsychological impairments during childhood.

Infant manual performance during reaching and grasping for objects moving in depth

Few studies have investigated manual performance in infants when reaching and grasping for objects moving in directions other than across the fronto-parallel plane. The present preliminary study explored object-oriented behavioral strategies and side preference in 8- and 10-month-old infants during reaching and grasping for objects approaching in depth from three positions (midline, and 27° diagonally from the left and right). Effects of task constraint by using objects of three different types and two sizes were further examined for behavioral strategies and hand opening prior to grasping. Additionally, assessments of hand preference by a dedicated handedness test were performed. Regardless of object starting position, the 8-month-old infants predominantly displayed right-handed reaches for objects approaching in depth. In contrast, the older infants showed more varied strategies and performed more ipsilateral reaches in correspondence with the side of the approaching object. Conversely, 10-month-old infants were more successful than the younger infants in grasping the objects, independent of object starting position. The findings regarding infant hand use strategies when reaching and grasping for objects moving in depth are similar to those from earlier studies using objects moving along a horizontal path. Still, initiation times of reaching onset were generally long in the present study, indicating that the object motion paths seemingly affected how the infants perceived the intrinsic properties and spatial locations of the objects, possibly with an effect on motor planning. Findings are further discussed in relation to future investigations of infant reaching and grasping for objects approaching in depth.

Abnormal interhemispheric motor interactions in patients with callosal agenesis

During unilateral hand movements the activity of the contralateral primary motor cortex (cM1) is increased while the activity of the ipsilateral M1 (iM1) is decreased. A potential explanation for this asymmetric activity pattern is transcallosal cM1-to-iM1 inhibitory control. To test this hypothesis, we examined interhemispheric motor inhibition in acallosal patients. We measured fMRI activity in iM1 and cM1 in acallosal patients during unilateral hand movements and compared their motor activity pattern to that of healthy controls. In controls, fMRI activation in cM1 was significantly higher than in iM1, reflecting a normal differential task-related M1 activity. Additional functional connectivity analysis revealed that iM1 activity was strongly suppressed by cM1. Furthermore, DTI analysis indicated that this contralaterally induced suppression was mediated by microstructural properties of specific callosal fibers interconnecting both M1s. In contrast, acallosal patients did not show a clear differential activity pattern between cM1 and iM1. The more symmetric pattern was due to an elevated task-related iM1 activity in acallosal patients, which was significantly higher than iM1 activity in a subgroup of gender and age-matched controls. Also, interhemispheric motor suppression was completely absent in acallosal patients. These findings suggest that absence of callosal connections reduces inhibitory interhemispheric motor interactions between left and right M1. This effect may reveal novel aspects of mechanisms in communication of two hemispheres and establishment of brain asymmetries in general.

Different assessment tasks produce different estimates of handedness stability during the eight to 14 month age period

Using 150 infants (57% males), two common tasks for assessing infant hand-use preferences for acquiring objects were compared for their ability to detect stable preferences during the age period of eight to 14 months. One task assesses the preference using nine presentations of objects; the other uses 32 presentations. Monthly classifications of hand preference for each task were determined by either a commonly used a decision criterion in which one hand is used 50% more often than the other or a criterion based on proportion of hand-use difference that exceeds a conventional alpha probability of 0.05. The seven monthly assessments provided by the two tasks also were examined for latent classes in their developmental trajectories. The two tasks were significantly different for both their identification of latent classes and their monthly classification of the infant's hand-use preference. The 32 presentations yielded three developmental trajectories (45% right preferring, 5% left preferring, and 50% no clear preference) whereas the nine presentations revealed only two trajectories (70% right, 30% no preference). The nine presentations task, with the 50% proportion decision criterion, was very generous in classifying right and left-preferring infants at each month but produced greater fluctuations across months compared to the 32 presentation task with an alpha decision criterion. Both tasks revealed that a large proportion of infants are still developing a hand-use preference during this age period. Recommendations are made for examining the development of hand-use preferences and their relation to the development of other neuropsychological functions.

Social encouragement can influence manual preference in 6 month-old-infants

The purpose of this study was to investigate the influence of social encouragement on infants’ hand movements, in particular on manual preference. Thirty-six infants were observed at 5.5 months. In a first step, their spontaneous manual preference was recorded with an object placed at the midline position. The second step consisted in encouraging infants to use their non-preferred hand by putting the object near that hand and congratulating them. The third step was similar to the first one (object placed at the midline position) except that the infant continued to be congratulated when (s)he used the non-preferred hand for reaching the object. Results showed that half of the infants exhibited a spontaneous manual preference and that a majority of these infants could use their non-preferred hand when verbally encouraged. Moreover, infants showing a left hand preference modified their hand-use more easily than infants showing a right hand preference. Although our findings reveal only a temporary and short-term influence of the social context, results are discussed in light of a socio-cognitive perspective whereby social encouragement can model manual preference, in particular its strength and stability.

Highlights

• At 5.5 months, a manual preference was observed in 47.2% of the infants.

• The preference for the left hand was observed in 35.3% of the infants who presented a manual preference.

• Left-handers change more easily their hand-use than right handers.

Hand preference status and reach kinematics in infants

Infants show age-related improvements in reach straightness and smoothness over the first years of life as well as a decrease in average movement speed. This period of changing kinematics overlaps the emergence of handedness. We examined whether infant hand preference status is related to the development of motor control in 53 infants ranging from 11 to 14 months old. Hand preference status was assessed from reaching to a set of 5 objects presented individually at the infant's midline; infants were classified into 'right preference' or 'no preference' groups. Three-dimensional (3-D) recordings were made of each arm for reaches under two distinct conditions: pick up a ball and fit it into the opening of a toy (grasp-to-place task) or pick up a Cheerio® and consume it (grasp-to-eat task). Contrary to expectations, there was no effect of hand preference status on reach smoothness or straightness for either task. On the grasp-to-eat task only, average speed of the left hand differed as a function of hand preference status. Infants in the no preference group exhibited higher left hand average speeds than infants in the right preference group. Our results suggest that while behavioral differences in the use of the two hands may be present in some infants, these differences do not appear to be systematically linked to biases in motor control of the arms early in development.

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.

Agenesis of the corpus callosum: classifying functional manifestations with the ICF-CY

PURPOSE

Agenesis of the corpus callosum (ACC) is a congenital condition in which the corpus callosum fails to develop fully. In the literature, ACC has been broadly conceptualized and inconsistently described. This article demonstrates how the universal language of the International Classification of Functioning, Disability and Health-Children and Youth can increase the specificity with which researchers and clinicians describe the variable manifestations of ACC.

METHODS

The database for this article was based on a review of 83 studies on developmental and neuropsychological manifestations of congenital ACC in children and adolescents. First, the extent to which the findings on ACC could be documented using the taxonomic codes in the ICF-CY was examined. Next, the findings from each study were mapped onto the ICF-CY to summarize the distribution of clinical features reported in the literature.

RESULTS

There was a high degree of correspondence between the reported findings and the taxonomic codes of the ICF-CY. The distribution of clinical features was discussed.

CONCLUSIONS

This taxonomic application advances the ICF-CY as a common language for researchers and clinicians who work with children who have ACC. Implications for Rehabilitation Agenesis of the corpus callosum (ACC) is a condition that has been broadly conceptualized and inconsistently described in research and practice. The variable clinical manifestations of children with ACC can be most effectively described using the ICF-CY. The application of the ICF-CY to conditions with highly variable clinical manifestations, like ACC, positively impacts research and practice.

The genetic relationship between handedness and neurodevelopmental disorders

Handedness and brain asymmetry have been linked to neurodevelopmental disorders such as dyslexia and schizophrenia. The genetic nature of this correlation is not understood. Recent discoveries have shown handedness is determined in part by the biological pathways that establish left/right (LR) body asymmetry during development. Cilia play a key role in this process, and candidate genes for dyslexia have also been recently shown to be involved in cilia formation. Defective cilia result not only in LR body asymmetry phenotypes but also brain midline phenotypes such as an absent corpus callosum. These findings suggest that the mechanisms for establishing LR asymmetry in the body are reused for brain midline development, which in turn influences traits such as handedness and reading ability.

Common variants in left/right asymmetry genes and pathways are associated with relative hand skill

Humans display structural and functional asymmetries in brain organization, strikingly with respect to language and handedness. The molecular basis of these asymmetries is unknown. We report a genome-wide association study meta-analysis for a quantitative measure of relative hand skill in individuals with dyslexia [reading disability (RD)] (n = 728). The most strongly associated variant, rs7182874 (P = 8.68 × 10(-9)), is located in PCSK6, further supporting an association we previously reported. We also confirmed the specificity of this association in individuals with RD; the same locus was not associated with relative hand skill in a general population cohort (n = 2,666). As PCSK6 is known to regulate NODAL in the development of left/right (LR) asymmetry in mice, we developed a novel approach to GWAS pathway analysis, using gene-set enrichment to test for an over-representation of highly associated variants within the orthologs of genes whose disruption in mice yields LR asymmetry phenotypes. Four out of 15 LR asymmetry phenotypes showed an over-representation (FDR ≤ 5%). We replicated three of these phenotypes; situs inversus, heterotaxia, and double outlet right ventricle, in the general population cohort (FDR ≤ 5%). Our findings lead us to propose that handedness is a polygenic trait controlled in part by the molecular mechanisms that establish LR body asymmetry early in development.

Handedness for bimanual coordinated actions in infants as a function of grip morphology

We investigated the emergence of bimanual handedness in tasks involving complementary roles for the two hands, one hand holding a base object and the other hand removing several pieces from the base object. Infants aged 12, 16, and 20 months were tested on bimanual tasks differing mainly in the precision of the movement required to remove the pieces. The results show that the right hand was more often used than the left hand not only to grasp the base object but also to remove the pieces, often after transferring the base object from the right to the left hand. As of 12 months of age, right hand preference for the active part of the bimanual task was stronger in the precision grip than in the whole-hand grip tasks. These results indicate that even though infants often do not anticipate that they will need their preferred hand to remove the pieces, they show clear handedness in such coordinated repeated bimanual actions, and do so to a greater degree on tasks requiring precision grip than on ones requiring whole-hand grip. These results agree with the notion that handedness develops very early and is related to the precision required from the active hand.

Complete corpus callosum agenesis: can it be mild?

Corpus callosum agenesis is a relatively common brain malformation. It can be isolated or included in a complex alteration of brain (or sometimes even whole body) morphology. Etiology and pathogenetic mechanisms have been better understood in recent years due to the availability of more adequate animal models and the relevant progresses in developmental neurosciences. We present the case of a girl with a complete agenesis of the corpus callosum discovered at birth. She had mild learning difficulties, but reached satisfactory levels of autonomy after an individually tailored rehabilitative treatment. Her story is discussed in light of recent findings, which emphasize the possibility to exploit brain plasticity and the utility of an individually tailored approach, defined on the basis of a dialogue with the family and the patient.

Handedness for grasping objects and declarative pointing: a longitudinal study

It is still unclear whether infants become right-handed because of their left-hemisphere specialization for language (through gestural communication for instance), whether they speak predominantly with their left hemisphere because of this hemisphere's superiority in controlling sequential actions which first results in right-handedness, or whether the two lateralization processes develop independently. To tackle this question, we followed 26 human infants from 8 to 20 months to evaluate the temporal relationship between the emergence of hand preference for grasping objects and for declarative pointing (communicative gesture). Our results show that when grasping and pointing are compared in similar conditions, with objects presented in several spatial positions, the tendency to use the right hand is significantly larger for pointing than for grasping, and both hand preferences are loosely correlated. This suggests that, at least at the age studied here, hand preferences for grasping and for declarative pointing develop relatively independently.

Neurodevelopmental outcome following prenatal diagnosis of an isolated anomaly of the corpus callosum

OBJECTIVES

To assess the ability of prenatal ultrasound and magnetic resonance imaging (MRI) to diagnose isolated anomalies of the corpus callosum (ACC) and to further document the long-term prognosis following diagnosis.

METHODS

This was a prospective case-control study carried out between 1999 and 2004. Diagnosis was made by a combination of ultrasound and MRI. All infants were examined by a neuropediatrician and parents consented to answer questionnaires (CDI, Ireton's Child Developmental Inventory) in 22 cases, which were matched with 44 control infants. The CDI was used to assess neurodevelopmental outcome in cases and controls. Mean DQ-CDI (development quotient calculated from CDI) values and frequencies of abnormal results were compared between groups, and a meta-analysis of previous studies was performed.

RESULTS

The diagnosis of ACC was made prenatally and confirmed postnatally in 175 cases. The diagnosis was thought to be isolated ACC in 88/175 (50%) cases. Sixty of these 88 cases (68%) underwent termination of pregnancy and one died in utero. Twenty-seven were liveborn, of which 26 were followed up for a median of 50 (range, 30-74) months. Additional anomalies were diagnosed postnatally in four (15%) of these 26 neonates. The control group was significantly better (P < 0.05) compared with the cases diagnosed prenatally with isolated ACC with respect to gross motor, fine motor, language comprehension, numbers and general development, and it was marginally better for letters (P = 0.066). Seven of 26 (27%) (95% CI, 13-46%) infants with ACC over the age of 30 months had neurodevelopmental delay, compared with only one case with borderline developmental delay among the 44 controls (P = 0.006).

CONCLUSION

Prenatal diagnosis of ACC by a combination of ultrasound and MRI is reliable. However, the isolated nature of the anomaly could only be assessed in 85% of our cases. Since counseling is provided at the time of prenatal diagnosis, our population of isolated ACC included the cases that were missed prenatally as being ACC with associated anomalies. A meta-analysis of nine studies suggests that the development of children diagnosed prenatally with isolated ACC is normal in up to 70% (CI 95%, 56-83%) of cases. This means that the prospective risk of neurodevelopmental delay for a fetus with ACC described as isolated prenatally is 27%, compared with 15% for an infant whose diagnosis of isolated ACC is confirmed postnatally.

Corpus callosum agenesis and rehabilitative treatment

Corpus callosum agenesis is a relatively common brain malformation. It can be isolated or included in a complex alteration of brain (or sometimes even whole body) morphology. It has been associated with a number of neuropsychiatric disorders, from subtle neuropsychological deficits to Pervasive Developmental Disorders.

Etiology and pathogenetic mechanisms have been better understood in recent years, due to the availability of more adequate animal models and the relevant progresses in developmental neurosciences. These recent findings are reviewed (through a MedLine search including papers published in the last 5 years and most relevant previously published papers) in view of the potential impact on children's global functioning and on the possible rehabilitative treatment, with an emphasis on the possibility to exploit brain plasticity and on the use of the ICF-CY framework.

Atypical functional lateralization in children with fetal alcohol syndrome

In order to explore effects of prenatal alcohol exposure on functional lateralization, item tasks measuring preferences of hand, foot, eye, and ear were administered to a sample of 23 children diagnosed with fetal alcohol syndrome (FAS) compared with typically developing (TD) children. In addition, a dichotic listening task was administered to a subsample of 11 children with FAS and a TD group of comparable age, sex and handedness. The children with FAS were characterized by increased nonright-handedness compared with TD children. No differences were evident for preferential use of foot, eye, or ear. Moreover, children with FAS displayed more right ear extinctions during dichotic listening relative to TD children, indicating a lack of right ear advantage. The results add to findings of decreased manual asymmetry and less left-lateralized speech perception in children with developmental disorders, and are further discussed in relation to the high incidence of callosal abnormalities in alcohol-exposed children.

Reaching and grasping movements in infants at risk: a review

Although the influence of intrinsic and extrinsic factors on the development of reaching and grasping skills in typical infants has been extensively described in the literature, the effect of such factors on at-risk infants is still poorly understood. Therefore, the aims of the present study were to analyze the scientific publications, from 1980 to 2008, about factors influencing reaching and grasping movements in infants at risk and to describe methodological procedures used in the studies under review. A bibliographical review on empirical studies indexed on Medline, Lilacs and Science Direct data bases was done, using as keywords the terms: "reaching movements", "grasping", "catching", "prehension", "infants", "children", "risk", "deficit", "impairment" and "delay". 127 articles were identified, and 11 were selected. The following risk conditions were assessed in the papers: prematurity, cerebral palsy, Down syndrome, intrauterine cocaine exposure and agenesis of corpus callosum. Methodological issues as well as the intrinsic and extrinsic factors manipulated in the experiments are discussed in the light of changes in theoretical approach to motor behavior.

Increased Frequency of Left-Handedness in Patients with Unilateral Coronal Synostosis

Objective:

Left-handedness reportedly has been more common in persons with neurological afflictions (e.g., stroke) and malformations (e.g., cleft lip with or without cleft palate) that demonstrate marked unilateral involvement. Coronal synostosis is also more frequently unilateral, affecting the right side more commonly than the left. We sought to compare left-handedness in patients with unilateral coronal synostosis versus healthy controls.

Subjects:

All patients aged 3 years or older with nonsyndromic unilateral coronal synostosis and healthy controls recruited by pediatricians blinded to the study.

Main Outcome Measures:

Prospective data obtained for all participants included age, gender, and handedness. In patients with unilateral coronal synostosis, the side of synostosis and age at surgery were documented. Left-handedness in the study and control groups was compared using chi-square analysis. Left-handedness also was analyzed in the study group according to side of fusion.

Results:

Eighty-six patients with nonsyndromic unilateral coronal synostosis comprised the study group; there were 96 controls. The mean ages of the study (8.8 years) and control groups (9.8 years) were not statistically different (p > .05). There were more girls in the study group (67%) than in the control group (56%), but this difference was not statistically significant (p > .05). Left-handedness was documented in 30.2% of the study group and 11.4% of the control group (p < .005). Left-handedness was twice as common in patients with left versus right unilateral coronal synostosis (44.4% versus 20.4%; p < .05).

Conclusions:

Left-handedness is nearly three times more common in patients with unilateral coronal synostosis than in controls and four times more likely in patients with left-sided fusion.

Reaching and grasping a moving object in 6-, 8-, and 10-month-old infants: laterality and performance

The goal of this study was to investigate some of the visuo-motor factors underlying an infant's developing ability to grasp a laterally-moving object. In particular, hand preference, midline crossing, and visual-field asymmetry were investigated by comparing performance as a function of the object's direction of motion. We presented 6-, 8-, and 10-month-old infants with a graspable object, moving in a circular trajectory in the horizontal plane. Six-month-old infants reached for the object with the ipsilateral hand and grasped it with the contralateral hand. Eight-month-old infants showed a strong right-hand bias for both reaching and grasping. Ten-month-old infants showed a greater diversity of strategy use including bimanual and successful ipsilateral grasping following ipsilateral reaching in both directions of motion. Thus, motor constraints due to spatial compatibility, hand preference and bimanual coordination (but not midline crossing) must be taken into account to understand age differences in grasping a moving object.