Developmental correlates of handedness in a national sample of 11-year-olds

Association of intrauterine and early life factors with uterine leiomyomata in black women

PURPOSE

Uterine leiomyomata (UL) are the primary indication for hysterectomy and are 2-3 times more common in black than white women. Previous studies indicate that early life may be a critical time window of susceptibility to UL. We assessed the association of UL with selected intrauterine and early life factors, expanding on previous research by using a prospective design and validated data on exposure and disease.

METHODS

During 1997-2009, we followed 23,505 premenopausal women aged 23-50 years for new diagnoses of UL in the Black Women's Health Study. We used Cox regression models to compute incidence rate ratios (IRR) and 95% confidence intervals, adjusting for potential confounders.

RESULTS

During 12 years of follow-up, there were 7268 incident UL cases diagnosed by ultrasound (n = 5727) or surgery (n = 1541). There was little evidence of an association between UL and birth weight, gestational age, or exposure to soy formula in infancy. Significant associations were found for being first born, foreign born, or exposed to passive smoke in childhood, but the associations were weak, with IRRs ranging from 1.06 to 1.12.

CONCLUSIONS

These findings do not support the hypothesis that intrauterine and early life factors are strongly related to UL risk.

HAND PREFERENCE IN TURKISH POPULATION

The distribution of hand preference (self report) was studied in siblings and their parents originating from all parts of Turkey (N = 22,461). In total sample and siblings, there were significantly more right-handed women than men, and significantly more left-handed men than women--no significant sex difference for parents' handedness. The relative number for the right-handed parents significantly exceeded that for the right-handed siblings; the relative number for the left-handed siblings significantly exceeded that for the left-handed parents. It was concluded that there may be a sex difference in hand preference, but being only about 1% more left-handed men, and only about 1% more right-handed women; the right-handedness in new generation (siblings) is less than that in old generation (parents), due to freeing from cultural pressures against the left-hand use in everyday activities.

Handedness in Great Britain

Two large British databases of handedness assessed by writing hand at 10-11 years of age were analysed by geographical region. Left-handedness was found to vary significantly across regions according to one survey but not the other. In both data sets, left-handed writing was significantly more frequent in England than in Scotland and Wales combined. Possible reasons for this difference are discussed.

Cultural and environmental pressure against left-hand preference in urban and semi-urban Malawi

The study assessed views of teachers, pupils and their guardians on left-hand preference. Seventy-five percent of the responders indicated that the left hand should not be preferred for habitual activities and 87.6% of them indicated that left-handers should be forced to change the hand. Gender had significant effect on the view on left hand preference (df = 1, OR (odds ratio) = 0.465, p = 0.027). Giving a handshake when greeting a person, drawing and writing were the three top target activities against left-hand preference. An assumption that the left hand is less skilled and less powerful than the right one was the most common reason for negative view on left-hand use. Most of volunteers reported that parents and close relatives were the primary group of people who usually discourage left-hand use. Eighty point one percent of the responders indicated that people should stop preferring the left hand as soon as somebody noticed their left-handedness. The results indicated that cultural and environmental pressures might significantly affect visibility of left-handedness in urban Malawian populations.

Lateral preferences in children with intellectual deficiency of idiopathic origin

The goal of this study was to evaluate lateral preferences in a population of children with intellectual deficiency of idiopathic origin, compared with those of typically developing (TD) children. Two groups of children with mild or moderate intellectual deficiency were observed. Handedness (using a 10-item test and Bishop's card-reaching task), eyedness and footedness were studied. The younger group consisted of sixteen 10- to 11-year olds; the older group comprised fourteen 12- to 14-year olds. A control group of fifteen TD children was matched for age with the younger group of intellectually deficient (ID) children. The results show that the occurrence of left-handedness is not higher in children with ID of unknown origin than in age-matched TD children. However, we observed a marginally reduced tendency toward right-handedness in ID than in TD children: more mixed-handers among ID than TD children; test-retest consistency of hand preference significantly lower in the 10- to 11-year-old ID children than in the age-matched TD children; greater tendency of ID children to use their nonpreferred left hand when the card was presented to the left, as compared with TD children. Left-eyedness and crossed hand-eye preference were also more frequent in ID than in age-matched TD children. No age-related difference in laterality was found in ID children. These results partially support other studies indicating that less rightward asymmetry is associated with intellectual deficiency in children.

On the other hand

This paper presents a brief overview of the past and current state of handedness research illustrating some of the controversies. It emphasizes two aspects: the lack of agreement on the behavior that indicates to which hand-use group (left or right) an individual belongs, and the reasons for preferring one hand rather than the other for various manual activities.

Androgenic influences on neural asymmetry: Handedness and language lateralization in individuals with congenital adrenal hyperplasia

This study tested the hypothesis that prenatal androgen levels influence hand preferences and language lateralization, two manifestations of neural asymmetry. Participants were individuals with congenital adrenal hyperplasia (CAH, a genetic disorder that results in excess adrenal androgen production beginning prenatally) (40 females; 29 males) and their unaffected relatives (29 females; 30 males) who ranged in age from 12-45 years. The Edinburgh-Crovitz Inventory and the performance of five simple tasks (the Handedness Activities Test) were the measures of hand preferences, and a dichotic listening task composed of consonant-vowel nonsense syllables was the measure of language lateralization. No sex differences were observed among relative controls in hand preferences or language lateralization. Male participants with CAH were less consistently right-handed for writing than unaffected male relatives, when those who had been forced to switch writing hands from left to right were considered with left-handers as being not consistently right-handed. There were no other significant differences between individuals with CAH and unaffected relatives. These results do not support the hypothesis that prenatal androgens influence language lateralization, nor do they support the Geschwind-Behan-Galaburda model that posits a key role for testosterone in the development of cognitive problems in males, secondary to changes in hemispheric development and cognitive lateralization. Hormonal influences on handedness, although not always consistent, may be more likely. However, given that sex differences in both language lateralization and handedness are small, it is possible that limited sample size precludes the detection of consistent group differences.

Hormonally active agents in the environment and children's behavior: assessing effects on children's gender-dimorphic outcomes

BACKGROUND

Early sex hormone exposure contributes to gender-dimorphic behavioral development in mammals, including humans. Environmental toxicants concentrated in contaminated sport fish can interfere with the actions of sex steroids.

METHODS

This study developed an outcome variable by combining gender-dimorphic behaviors that differentiates boys and girls. Offspring of participants in the New York State Angler Cohort Study (NYSACS) were targeted in a parent-report postal survey. Instruments were selected based on findings of gender differences in the general population.

RESULTS

A linear discriminant function model incorporating three gender behavior scales correctly classified the sex of 97.7% of children (252 boys and 234 girls) from a random NYSACS sample. The discriminant function was cross-validated by correctly classifying the sex of 98.4% of children (457 boys and 425 girls) from the remaining NYSACS cases and 97.6% of children (154 boys and 142 girls) from an independent school sample. Within-sex stepwise multiple regression analyses revealed that masculine behavior increased among boys with age and with the number of years of maternal sport fish consumption. In girls, older age and previous live-born siblings were associated with more masculine behavior, whereas feminine behavior increased with the duration of breast feeding. These associations were replicated in an independent sample.

CONCLUSIONS

A linear discriminant function effectively transformed the binary classification of sex (male-female) to a bipolar continuum of gender (masculinity-femininity). Findings from this study are consistent with the hypothesis that environmental contaminants contribute to shifts in gender-role behavior. Future investigations will need to account for competing explanations of this effect.

Academic achievement and learning abilities in left-handers: guilt or gift?

The main purpose of this cross-sectional study was to compare the acceptance rate (AR) of left-handers (LHs) with that of right-handers (RHs) in the college entrance examination (CEE) for the national universities in Iran. During 5 successive years, fifty thousand participants in this exam were randomly sampled. We evaluated the relationships between AR and hand preference, sex, college admission (CA), entrance exam score (EES) and study areas: Mathematics, Natural Sciences, Humanities and Art. The acceptance rate of the LHs over the entire study period was significantly higher than that of the RHs (27.3% versus 24.3%, p < 0.0001). The mean score attained on examination by LHs was significantly higher than that of RHs in all study areas (p < 0.002). The acceptance rate of LHs in all study areas was higher but the difference reached statistical significance in the Art area only (p < 0.01). It is concluded that left-handers may be regarded as a heterogeneous large group consisting of different subgroups. Those who are able to compete for the college entrance examination score are even more successful than right-handers in terms of average EES and the rate of CA.

Hand preference and motor functioning in children with autism

This study examined three theories that have been proposed to explain the high rates of ambiguous hand preference in young children with autism. Twenty children with autism were matched with 20 children with developmental delays and 20 normally developing children. The groups were compared on measures of hand preference and motor skills. Results indicated that the lack of development of a hand preference in children with autism was not a direct function of their cognitive delay, as the children with developmental delays showed a dissimilar pattern of hand preference. The lack of a definite hand preference in the children with autism was also not due to a lack of motor skill development, as the children with developmental delays displayed similar levels of gross and fine motor skills without the accompanying lack of a definite hand preference. The finding that children with autism with a definite hand preference displayed better performance on motor, language, and cognitive tasks than children with autism who did not display a definite hand preference, however, provided support for the bilateral brain dysfunction hypothesis.

Language lateralization and handedness in women prenatally exposed to diethylstilbestrol (DES)

Hand preferences and language lateralization were assessed in women exposed prenatally to the synthetic estrogen, diethylstilbestrol (DES), and in their unexposed sisters. The DES-exposed women showed an increased degree of hand preference (regardless of direction) and were more likely to be left handed for writing. However, the groups did not differ significantly on a dichotic listening measure of language lateralization. Perhaps as a result of the alterations in hand preferences, the typical relationship between hand preferences and language lateralization was disrupted in the DES-exposed group. Also, within the DES-exposed group, exposure early in gestation correlated with left handedness whereas exposure late in gestation correlated with reduced left ear (right hemisphere) scores on the verbal dichotic task. Results are discussed in terms of theoretical perspectives predicting hormonal influences on sexual differentiation of hemispheric asymmetry and in terms of separate critical periods for hormonal effects on individual sexually differentiated characteristics.

Sexual orientation and handedness in men and women: a meta-analysis

Recent findings suggest that sexual orientation has an early neurodevelopmental basis. Handedness, a behavioral marker of early neurodevelopment, has been associated with sexual orientation in some studies but not in others. The authors conducted a meta-analysis of 20 studies that compared the rates of non-right-handedness in 6,987 homosexual (6,182 men and 805 women) and 16,423 heterosexual (14,808 men and 1,615 women) participants. Homosexual participants had 39% greater odds of being non-right-handed. The corresponding values for homosexual men (20 contrasts) and women (9 contrasts) were 34% and 91%, respectively. The results support the notion that sexual orientation in some men and women has an early neurodevelopmental basis, but the factors responsible for the handedness-sexual orientation association require elucidation. The authors discuss 3 possibilities: cerebral laterality and prenatal exposure to sex hormones, maternal immunological reactions to the fetus, and developmental instability.

Voice, speech and language characteristics of children with Prader-Willi syndrome

Eleven individuals with Prader-Willi syndrome (PWS), aged between 4 and 25 years, were compared with II non-PWS children of the same sex, age, body mass index and IQ level. Voice, speech and language skills were generally impaired in subjects with PWS. Oral motor function, pitch level and resonance were specifically disordered and clearly differentiated the two groups from each other. Certain biological perinatal factors separated subjects with PWS from other obese children and adolescents, but did not differentiate within the group with PWS and could not account for the speech/language problems. Underlying cerebral dysfunction, combined with a characteristic anatomy of the mouth and larynx in PWS, contributes to altered voice, speech and language function.

Cerebral lateralization is delayed in children who later develop schizophrenia

The origins of schizophrenia are obscure. One suggestion is that it represents a component of the genetic variation associated with the establishment of dominance in one or other cerebral hemisphere, a mechanism that has been crucial in the evolution of language. Indices of cerebral hemispheric dominance (hand, foot and eye preference, speed of checking squares) recorded on the 16,980 children in the UK National Child Development Study cohort were examined in relation to psychiatric admission by the age of 28 years. Diagnoses were established by the application of Present State Examination criteria to case notes. Pre-schizophrenic children (n = 34-36) were more likely (p < 0.0003) to be rated by their mothers as ambidextrous at the age of 7 years, and at 11 years were less (p < 0.01) strongly right-handed than their peers in the cohort population on a test of relative hand skill: children who later developed affective psychosis (n = 25) or neurosis (n = 60) did not differ significantly from controls. Delay in establishing dominance in one hemisphere could be the critical factor that predisposes to schizophrenia.

Handedness in women with intrauterine exposure to diethylstilbestrol

Completed forms containing the Edinburgh handedness inventory were received from 77 women exposed to diethylstilbestrol (DES) in utero. Laterality scores (LSs; range: -100 to +100) were calculated for each respondent based on the handedness inventory and were compared with LSs from 514 female controls. The handedness distribution in the DES daughters was significantly shifted away from strong righthandedness compared with the handedness distribution in the controls (chi-square = 22.0, P < 0.0001). Possible explanations for the association between handedness and DES exposure are presented, and aspects of handedness measurement are discussed.

The prevalence and origins of left hand preference in high risk infants, and its implications for intellectual, motor and behavioural performance at four and six years

This study investigates the origins of hand preference at 4 years in a cohort of 115 high risk and premature infants; the relationship between patterns of hand preference and intellectual, motor, temperament and behavioural status at 4 and 6 years; and evidence for brain injury in mediating the relationship between hand preference and development disorder. Increased left hand preference was independently associated with extreme prematurity, high neonatal risk, increased numbers of minor physical anomalies, lowered intellectual and motor abilities, and more difficult temperament. These findings supported the presence of intrauterine and neonatal pathological mechanisms leading to left hand preference in a small number of children. Neither poor function of the non dominant hand nor absence of a family history of left handedness could further define this pathological subgroup. Support for pathological mechanisms producing left handedness was found predominatly in the infants of high birth weight, whereas prevalence of left handedness was increased mainly among the extremely low birth weight infants. In this latter group the prevalence of left handedness was also increased among children of normal intelligence, suggesting that mechanisms other than brain damage lead to left hand preference in very premature infants.

A review of child health in the 1958 birth cohort: National Child Development Study

In the week 3-9 March 1958, 98% of all births in England, Scotland and Wales (approximately 17,000) were studied in the Perinatal Mortality Survey. The follow-up of surviving children, known as the National Child Development Study, comprises four major sweeps at ages 7, 11, 16 and 23. Medical examinations were conducted at each age, except at 23 when health was self-reported. Details of the child's family background and socio-economic circumstances were recorded, together with assessments of their social development and educational attainment. Seventy-six per cent of the target population were interviewed at age 23. The health of subjects in the 1958 cohort has been described in over 200 publications but there is no comprehensive account of findings from birth to age 23. This overview attempts to redress this. As new data are gathered from the study subjects at age 33, opportunities will exist to investigate associations between childhood factors and health in midlife. Data on their partners and children will be included, allowing studies of inter-generational and family health. Further indications of changing illness patterns will be possible from comparisons with data collected on earlier and later born cohorts.

Causes and associations of severe and persistent specific speech and language disorders in children

Eighty-two school-age children with severe and persistent specific speech and language disorders were studied. 71 had specific developmental language disorders, three had structural malformations (cleft palate) and eight had disorders acquired after a period of normal language development, including five with Landau-Kleffner syndrome. The sex ratio was 3.8 boys to one girl. Nearly half had a family history of speech-language disorder, with one in 5.2 affected siblings. Aetiological factors were found in 26 per cent: 11 per cent prenatal, 3 per cent perinatal and 12 per cent postnatal. 21 per cent had had a seizure and 7 per cent had had seizures after the age of eight. 29 per cent were left-handed, 90 per cent were clumsy and 22 per cent first walked after 18 months. The complex origins of specific speech and language disorders are discussed.

Using non-preferred hand skill to investigate pathological left-handedness in an unselected population

This paper considers whether pathological influences affect hand-preference among children with epilepsy or mental retardation, for whom there is no evidence of gross motor defect. Data on two tasks of manual skill were analysed for a group of over 12,000 children. The predicted association between poor skill with the non-preferred hand and left-handedness was confirmed for the match-sorting test, and was particularly strong among children with a neurological abnormality (excluding cerebral palsy). No association between poor skill and left-handedness was found for the preferred hand. The data agreed well with a model which estimates hand preference it it occurs on the previously preferred side. The probability of pathological left-handedness among left-handers in an unselected population is about 0.05--this is much higher for children with a history of neurological disease, epilepsy or mental retardation, and for children with poor performance of the non-preferred hand.

Pathologic left-handedness: does it exist?

The concept of pathologic left-handedness is reviewed, both from a historical and an empirical point of view. It is suggested that there is no adequate evidence to justify its continued use. The fact that the concept is still much used may be the result of a desire to restore to the brain its lost symmetry, by allowing Dax's Law once more to be true.

The relationship of handedness to the cognitive, language, and visuo-spatial skills of autistic patients

The relationship between hand preference, age, and developmental functioning was examined in 70 autistic patients. Unilateral or mixed handedness appeared to be stabilized by the age of five years. Patients with established hand lateralization tended to function better in all developmental areas including intelligence, language, and visuospatial abilities. It is a tenable hypothesis that the presence or absence of hand lateralization by age five may be an important predictor of outcome in autism.

Handedness and birth stress

The relationship between left-handedness and birth complications was studied. No evidence of any association was found in either 2 retrospective studies, or 1 large prospective study.

Hand preference and personality traits

The relationship between hand preference (determined by questionnaire) and some personality trait scores was examined. The analysis revealed that males' mean neuroticism score differed between right, mixed and left handers. Right and left hand writers did not differ in mean personality scores.

Right-handedness: a consequence of infant supine head-orientation preference?

Most newborn infants (65 percent) preferred to lie with their heads turned to the right, whereas 15 percent showed a distinct preference for the left. Orientation preference is maintained for at least 2 months and predicts preferential hand use in reaching tasks at both 16 and 22 weeks. Right head-orientation preference in early infancy may contribute to the early development of right-handedness.

Hand preference and components of I.Q

An account is given of the hand preferences (measured by questionnaire) of 687 individuals living in a Cambridge suburb. The proportions of right, mixed and left handers differed according to the classification used. Verbal and Performance I.Q. component scores were examined in relation to hand preference. For all classifications, left handers' overall Verbal I.Q. was significantly higher than their Performance I.Q. score, whereas right and mixed handers' Performance I.Q. scores were greater than their Verbal I.Q.s. Left handers scored higher than right and mixed handers on Verbal I.Q. but lower on Performance I.Q. The relationships between patterns of handedness, I.Q. component scores and cerebral dominance are discussed.

Sex and lateral asymmetry of the finger ridge-count

In a sample 719 individuals, the bimanual difference in ridge-count (right minus left) differed only slightly between the two sexes, the mean difference being 0-621 (females minus males). This is not statistically significant, but further evidence suggests that this difference may be real.