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PubMed2002

Skeletal biology, functional asymmetry and the origins of "Handedness".

The past decade has witnessed the (re)emergence of a debate as to whether handedness is apomorphic within hominins. There are both qualitative and quantitative arguments, some which draw non-human primates into the handed sphere and others which exclude them. Ultimate questions concern origins of structural asymmetry of both brain and body and lateralized behaviours with implications for tool use and language. Lateralization is thus an important realm of phylogenetic study, and archaeologists and psychologists alike have sought to identify handedness within material culture. However, hand preference for tool manufacture and use among extant non-human primates, such as Cebus and Pan, suggests that the archaeological record may well be mute regarding the origins of laterality. In this paper, an argument is put forward positioning skeletal biology as a viable approach to the handedness origins issue. Behaviour is a mediator of the complementary processes of geometric modelling (change in size and shape) and histological remodelling (disuse osteopenia; microfracture repair); therefore, directional asymmetry in the pattern of skeletal modelling and remodelling is a putative signal of lateralized activity.

Animals↗
PubMed2001

Cerebral asymmetry and the effects of sex and handedness on brain structure: a voxel-based morphometric analysis of 465 normal adult human brains.

We used voxel-based morphometry (VBM) to examine human brain asymmetry and the effects of sex and handedness on brain structure in 465 normal adults. We observed significant asymmetry of cerebral grey and white matter in the occipital, frontal, and temporal lobes (petalia), including Heschl's gyrus, planum temporale (PT) and the hippocampal formation. Males demonstrated increased leftward asymmetry within Heschl's gyrus and PT compared to females. There was no significant interaction between asymmetry and handedness and no main effect of handedness. There was a significant main effect of sex on brain morphology, even after accounting for the larger global volumes of grey and white matter in males. Females had increased grey matter volume adjacent to the depths of both central sulci and the left superior temporal sulcus, in right Heschl's gyrus and PT, in right inferior frontal and frontomarginal gyri and in the cingulate gyrus. Females had significantly increased grey matter concentration extensively and relatively symmetrically in the cortical mantle, parahippocampal gyri, and in the banks of the cingulate and calcarine sulci. Males had increased grey matter volume bilaterally in the mesial temporal lobes, entorhinal and perirhinal cortex, and in the anterior lobes of the cerebellum, but no regions of increased grey matter concentration.

Adolescent↗
PubMed1992

Human handedness and the concept of developmental stability.

A model is proposed to explain the etiology of pathological handedness. Developmental instability, caused by elevated genotypic homozygosity, environmental disturbances, or their interaction, overrides programmed laterality and handedness in the same way that it perturbs the bilaterally symmetrical expression of morphological and metric traits. The model predicts that pathological handedness should be elevated among individuals with higher than average homozygosity and individuals who have developed under unfavorable uterine environments. Suggestions are offered for specific populations in which the predictions may be tested.

Functional Laterality↗
PubMed1993

Genetic and behavioral tests of the McManus hypothesis relating response to selection for lateralization of handedness in mice to degree of heterozygosity.

McManus advanced a genetic hypothesis to explain differences of lateralization between HI and LO lines of mice selectively bred for degree of handedness. It states that lateralization is a function of heterozygosity. Specifically it predicts that (a) the HI line will be more heterozygous than the LO line and (b) populations with a greater average heterozygosity (AH) will be more strongly lateralized. Both genetic and behavioral predictions were tested here. Results using coat color and biochemical variants show that AH in the HI line is somewhat less (not greater) than that in the LO line. The handedness of HET control mice and HI by LO reciprocal hybrids, where AH is greater than that of the HI line, exhibits lessened (not greater) lateralization. Results reject the heterozygosity hypothesis. A model for the inheritance of human handedness that accounts for difficulty in detecting heritable differences in degree of asymmetry is presented.

Animals↗
PubMed1985

Handedness and cognitive functions in pervasive developmental disorders.

This paper is concerned with what abnormal handedness in Pervasive Developmental Disorders (PDD) reveals about the presence, lateralization, and severity of cerebral dysfunction in this population. From previous work, it was predicted that left-handedness would be elevated in the sample and that mixed-handedness subjects should be more impaired than those with established hand dominance. A battery of cognitive and motor tests were administered to a group of PDD children with autistic symptoms, and performance was compared for the left-handed, right-handed, and mixed-preference children. It was found that left-handers tended to do better than right-handers on all cognitive measures, while the mixed-preference children tended to be the lowest on all cognitive measures. No differences were found on motor measures. An extension of the Satz (1972) model, assuming early brain damage, was developed to explain the superiority of the left-handed children; an alternative explanation assuming anomalous lateralization patterns in the natural left-handers was also suggested.

Adolescent↗
PubMed1978

Handedness in autistics, retardates, and normals of a wide age range.

Tests of handedness were carried out with 34 autistic children aged from 4 years 10 months to 18 years 11 months, and with sex-, age-, and IQ-matched retardates and sex- and age-matched normals. There were no significant differences between the groups on frequency of handedness, degree of righthand usage, or degree of dominant-hand usage. There was however a significant increase in the variance of dominant-hand usage from normals and retardates to autistics. These results were taken to indicate that earlier reports of handedness differences in young autistic children may reflect a developmental lag rather than a specific etiology of autism. Some support for this hypothesis was found from a comparison of age-trends between the groups. The relationship of such a developmental delay to the etiology of autism was discussed.

Adolescent↗
PubMed1996

Handedness in twins according to zygosity and chorion type: a preliminary report.

In the course of the East Flanders Prospective Twin Survey (EFPTS), handedness was assessed as part of a genealogical study (Meulemans et al., 1995) in 1616 twins (808 twin pairs) aged 6 to 28. Our findings are that, in this large population-based study with known placentation and zygosity, the often observed higher frequency of left-handedness in twins is confirmed, that it appears to be independent of zygosity and chorion type, and that the belief that discordant handedness in monozygotic twins represents mirror-imaging is mythical.

Adolescent↗
PubMedDate not supplied

Is there a link between Irritable Bowel Syndrome and left-handedness?: An exploratory study.

Recent research has found that people with Irritable Bowel Syndrome (IBS) and those with Inflammatory Bowel Disease (IBD) show a relative deficit in verbal IQ, compared to their own performance IQ, and the IQ of a healthy comparison group. It has been suggested that the elevated prevalence of left-handedness shown in previous studies investigating people with IBD is due to compromised left-hemisphere development. This may be associated with a decrement in certain cognitive functions such as verbal IQ. A shift in brain dominance from left to right has been found in many atopic and immunological diseases as well as in autonomic dysfunctions. It was uncertain whether this would apply to people with IBS, a functional disorder in which the cause or causes remain unclear. Therefore, the aim of this preliminary study was to investigate whether people with IBS have an increased prevalence of left-handedness. It was found that there was an association between IBS and left-handedness, showing that further research on this association both in IBS and other functional disorders (as well as on the similarities between IBS and IBD) is warranted.

Brain↗
PubMed2005

Sexual dimorphism and handedness in the human corpus callosum based on magnetic resonance imaging.

The corpus callosum (CC) is a major anatomical and functional commissure linking the two cerebral hemispheres. With MR imaging in the sagittal plane, the corpus callosum can be depicted in great detail. Mid-sagittal magnetic resonance images of 80 normal individuals were analyzed to assess whether or not the morphology of the corpus callosum and its parts are related to sex and handedness. The subjects were 40 males (20 right-handers and 20 left-handers) and 40 females (20 right-handers and 20 left-handers). The midsagittal area of the corpus callosum was divided into seven sub-areas using Witelson's method. The most striking morphological changes concerned left-handers, who had larger areas of the anterior body, posterior body and isthmus than right-handers. In addition, right-handed males had larger rostrums and isthmuses than right-handed females. These significantly increased areas were related to handedness in right-handed males. However, left-handed males had larger anterior and posterior bodies than right-handed males. In contrast, there was no significant difference between left-handers and right-handers in females. The areas of the rostrum and posterior body of the corpus callosum increased significantly with sex in males. Moreover, there were no significant age-related changes in the total corpus callosum and sub-areas of the corpus callosum. In conclusion, these anatomical changes in corpus callosum morphology require taking the sexual definition and dominant handedness into consideration.

Adult↗
PubMed2004

Left handedness and spine deformities in early adolescence.

The aim of this study was to investigate the relation between laterality and spine deformities in early adolescence, with special reference to sex differences. Interviews, anthropometric measurements and clinical examinations of body posture were carried out on a sample of 2546 schoolchildren, aged from 11 to 14 years, in seven elementary schools in the centre of Belgrade. Possible confounding factors (age, sex, body weight and body height) were controlled for. The overall prevalence of spine deformities (scoliosis and/or thoracic hyperkyphosis) in the investigated population was 11.8%, out of which there were 7.8% adolescents with scoliosis, 4.0% with thoracic hyperkyphosis, and 0.3% with both spine deformities. The prevalence of scoliosis was 2.7 times higher in girls compared to boys (11.7% vs. 4.3%) while the prevalence of thoracic hyperkyphosis was 1,6 higher among boys (5.0% vs. 3.2%). We found 7.6% of the schoolchildren examined to be left-handed. Left handedness was significantly related to scoliosis in girls (crude OR = 1.60 and 95% confidence interval = 1.01-2.54). Multivariate analysis showed that significant independent factors for scoliosis were female sex (p < 0.001), age (p = 0.01) and left handedness (p = 0.02). We did not find any appreciable relation between left handedness and thoracic hyperkyphosis in both sexes.

Adolescent↗
PubMed2006

A mathematical modelling for the cheliped regeneration with handedness in fiddler crab.

An enormously developed giant cheliped with the other small one characterizes the adult male fiddler crab. Some experiments with artificial severances of cheliped indicate that such a handedness in the cheliped size is maintained even after the regeneration of severed cheliped. Other experimental researches give some results about an unknown physiological system which controls the emergence and the regeneration of the handedness in the cheliped size. In this paper, with two hypothesized factors relevant to the regeneration of a severed cheliped, we propose a simple mathematical model to describe the experimental result about the cheliped regeneration with a handedness after the cheliped severance for the fiddler crab. Our model gives a suggestion about an underlying system for the cheliped regeneration in the fiddler crab or some other crustacean species.

Animals↗
PubMed1996

Handedness and the risk of tardive dyskinesia.

Previous results from five cross-sectional studies are conflicting about the relationship between hand preference and tardive dyskinesia (TD): two report a greater TD prevalence in left handers, and three report a greater prevalence in right handers. To help resolve these inconsistencies, the handedness-TD association was assessed in the Yale TD Study, a large prospective cohort investigation of outpatients maintained with neuroleptics. A consistent monotonic association was observed between the handedness score and TD incidence (p = 0.009). The estimated rate ratio, comparing left and mixed handers with pure right handers, adjusted for confounders, was 0.25 (95% confidence interval = 0.09, 0.70). The handedness effect (higher TD rate in right handers) was stronger for subjects with fewer negative symptoms, and it was stronger for men than for women. Although the specific biological mechanisms are unclear, these findings may reflect cerebral laterality in the pathophysiology of psychiatric disorders, possibly in combination with asymmetrical action of neuroleptic exposure.

Ambulatory Care↗
PubMed1993

Gender- and handedness-related differences of forebrain oxygenation and hemodynamics.

To elucidate gender- and handedness-related differences between the hemispheres of the brain in their metabolisms and hemodynamics, simultaneous monitoring by near-infrared (NIR) spectrophotometry of hemoglobin (Hb) in both hemispheres of the forebrain during the mirror drawing task (MDT) was performed. Bilaterally simultaneous increases of oxygenated Hb and decreases of deoxygenated Hb in forebrain occurred symmetrically in all cases of volunteer subjects except for two. There were gender- and handedness-related differences of hemodynamics between the hemispheres of the brain; NIR results showed that a large majority of women used both sides of the brain when concentrating on carrying out the MDT, whilst most men, especially left-handers, reacted mainly using the hemisphere which was 'dominant' according to handedness.

Adult↗
PubMed1983

Representation of short and long-range handedness in protein structures by signed distance maps.

A new representation is proposed of short and long-range handedness in protein structures, by signed distance maps. This representation, based on the co-ordinates of the C alpha atoms of proteins, does not require the assignment of specific regular structures. The short-range handedness along the chain in alpha-helical, beta-strand and turn segments is shown, as well as the handedness between two strands of beta-sheet structures and for crossover connections. Results are given for a beta alpha beta alpha beta folding unit of flavodoxin, a beta alpha beta unit of subtilisin, which contains a left-handed crossover connection, and the domain 1 of bovine beta-trypsin.

Flavodoxin↗
PubMed1983

The effect of sex, laterality and familial handedness on intellectual abilities.

This study assessed the relationship of sex, familial handedness and laterality to the intellectual abilities of 116 right-handed 12-14-yr-old subjects. Verbal scores were predicted by an interaction between familial handedness and the subject's own laterality. A strong right ear advantage for verbal stimuli and a large lateral difference between the ear advantage for verbal and nonverbal stimuli predicted high Verbal Intelligence scores for the strong right hand-eye preference subjects with family histories of dextrality. Conversely, attenuated ear advantage scores for verbal stimuli predicted high Verbal Intelligence scores for the strong right hand-eye familial sinistral subjects. Although the results were less consistent for Performance Intelligence scores, they were significantly and positively related to assessed hand-eye preference, and a significant interaction between familial handedness and the subject's own laterality was observed for the Object Assembly subtest. A strong left ear advantage for nonverbal stimuli predicted high scores for the strong right-preference familial dextral subjects and attenuated ear advantage for nonverbal stimuli predicted high scores for the strong right-preference familial sinistral subjects.

Adolescent↗
PubMed1985

Infant rightward asymmetries predict right-handedness in childhood.

Eight children for whom measures of head preference and hand visualization had been determined in infancy were evaluated by parent questionnaire for hand preference at ages 3.5-6 yr. All six infants who maintained their heads to the right became right-handed as predicted, while neither infant with a non-right head orientation developed handedness in the predicted direction, though neither became right-handed. Similarly, the five infants who had visualized their right hands more frequently than the left became right-handed children as predicted; of the three infants who did not visualize the right hand more frequently, none developed handedness as predicted. None of the infant measures correlated with childhood handedness. These results suggest support for the genetically based right shift factor proposed by ANNETT (Behav. Genet. 8, 227-249, 1978).

Child↗
PubMed1986

The influence of gender, handedness and head-turn on auditory asymmetries.

Subjects performed dichotic tasks with their heads turned 90 degrees to the left, 90 degrees to the right, and straight ahead. In Experiment 1 the stimuli were digits and the subjects varied in both sex and handedness. Right-handedness males showed a significant right-ear advantage under the head-right and head-straight conditions, while left-handed males and both right- and left-handed females failed to show any consistent ear asymmetries. In Experiment 2 the stimuli were melodies and the subjects were all right-handed. Head-turn had no significant influence on the results, and only the males showed a significant left-ear advantage. Overall, the results confirm previous findings that sex and handedness may influence auditory asymmetries, but fail to reveal systematic effects of head turn.

Adolescent↗
PubMed1986

Cerebral lateralization and handedness and their effects on verbal and spatial reasoning.

Consistent and inconsistent left- and right-handed male subjects completed four tests each of verbal and spatial reasoning. They also participated in tachistoscopic measures of verbal and spatial lateralization--consonant-vowel-consonant recognition and dot enumeration, respectively. The consistent handedness groups displayed significantly more lateralized patterns of cerebral organization that the inconsistent handedness groups. Increased lateralization was associated with superior performance on measures of spatial reasoning, but not on measures of verbal reasoning. Results are interpreted in terms of a competition hypothesis. No differences were found between the handedness groups on either the verbal or spatial reasoning tests.

Adolescent↗