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PubMed2003

Handedness and schizotypy in a Japanese sample: an association masked by cultural effects on hand usage.

Previous research has shown a robust association between schizotypy and mixed/ambiguous-handedness, but little is known about the universality of this relationship outside Western cultures. The present paper examines this issue in a sample of 413 Japanese students administered (in Japan) the Annett handedness questionnaire and a schizotypy scale (STA). Conventional analyses of current hand preference, using several indices derived from the Annett scale, mostly failed to replicate previous findings. However, there was a significant tendency for greater use of either hand in highly schizotypal males. Furthermore, a significant association between schizotypy and non-right-handedness was found--again only in males--after correcting for the effects of early switching of hand usage, presumed to be due to cultural pressure against left-handedness in Japanese society. These results were found to be highly convergent with findings previously reported for clinical schizophrenia.

Adolescent↗
PubMed2003

Asymmetry in the human primary somatosensory cortex and handedness.

Brain asymmetry is a phenomenon well known for handedness and language specialization and has also been studied in motor cortex. Less is known about hemispheric asymmetries in the somatosensory cortex. In the present study, we systematically investigated the representation of somatosensory function analyzing early subcortical and cortical somatosensory-evoked potentials (SEP) after electrical stimulation of the right and left median nerve. In 16 subjects, we compared thresholds, the peripheral neurogram at Erb point, and, using MRI-based EEG source analysis, the P14 brainstem component as well as N20 and P22, the earliest cortical responses from the primary sensorimotor cortex. Handedness was documented using the Edinburgh Inventory and a dichotic listening test was performed as a measure for language dominance. Whereas thresholds, Erb potential, and P14 were symmetrical, amplitudes of the cortical N20 showed significant hemispheric asymmetry. In the left hemisphere, the N20 amplitude was higher, its generator was located further medial, and it had a stronger dipole moment. There was no difference in dipole orientation. As a possible morphological correlate, the size of the left postcentral gyrus exceeded that of the right. The cortical P22 component showed a lower amplitude and a trend toward weaker dipole strength in the left hemisphere. Across subjects, there were no significant correlations between laterality indices of N20, the size of the postcentral gyrus, handedness, or ear advantage. These data show that asymmetry of median nerve SEP occurs at the cortical level, only. However, both functional and morphological cortical asymmetry of somatosensory representation appears to vary independently of motor and language functions.

Adult↗
PubMed2003

From mouth to hand: gesture, speech, and the evolution of right-handedness.

The strong predominance of right-handedness appears to be a uniquely human characteristic, whereas the left-cerebral dominance for vocalization occurs in many species, including frogs, birds, and mammals. Right-handedness may have arisen because of an association between manual gestures and vocalization in the evolution of language. I argue that language evolved from manual gestures, gradually incorporating vocal elements. The transition may be traced through changes in the function of Broca's area. Its homologue in monkeys has nothing to do with vocal control, but contains the so-called "mirror neurons," the code for both the production of manual reaching movements and the perception of the same movements performed by others. This system is bilateral in monkeys, but predominantly left-hemispheric in humans, and in humans is involved with vocalization as well as manual actions. There is evidence that Broca's area is enlarged on the left side in Homo habilis, suggesting that a link between gesture and vocalization may go back at least two million years, although other evidence suggests that speech may not have become fully autonomous until Homo sapiens appeared some 170,000 years ago, or perhaps even later. The removal of manual gesture as a necessary component of language may explain the rapid advance of technology, allowing late migrations of Homo sapiens from Africa to replace all other hominids in other parts of the world, including the Neanderthals in Europe and Homo erectus in Asia. Nevertheless, the long association of vocalization with manual gesture left us a legacy of right-handedness.

Animals↗
PubMed2002

Dermatoglyphics, handedness, sex, and sexual orientation.

Both handedness and dermatoglyphic asymmetry reflect early, prenatal influences and both have been reported to be associated with male sexual orientation; handedness has been related to female sexual orientation as well. Neurohormonal and developmental perturbation are two competing hypothesis that attempt to explain these connections. We attempted to replicate these associations and to extend dermatoglyphic asymmetry findings to women. Dermatoglyphic directional asymmetry and fluctuating asymmetry were unrelated to sexual orientation. Homosexual women, but not homosexual men, had highly significant increases in non-right-handedness compared with same-sex heterosexual controls. Although this pattern of results does not allow resolution of the two competing models, it does lend additional support to a biological basis of sexual orientation.

Adult↗
PubMed2002

Relationships among childhood sex-atypical behavior, spatial ability, handedness, and sexual orientation in men.

Moderate support was obtained in a sample of 101 gay, bisexual, and heterosexual males for the perinatal hormone theory, which hypothesizes that attenuated levels of androgens during critical periods of male fetal development fail to masculinize and defeminize the brain. Affected individuals develop female-typical sexual orientation (assessed here by a pie chart) and cerebral organization, reflected in visual-spatial abilities and gender nonconformity. Handedness, also thought to reflect in utero hormone exposure, was evaluated. Gay and bisexual males reported greater femininity and lesser masculinity than heterosexuals, with bisexuals intermediate in masculinity, suggesting a common biological mediator for homoeroticism and sex atypicality. Among bisexual males, increased masculinity was related to enhanced performance on all spatial tasks. Group mean differences in spatial ability and handedness were not found; however, among bisexuals, poorer visual-spatial performance predicted increased homoeroticism and right-handedness positively correlated with all spatial tasks. If perinatal hormones contribute to a generalized feminization of the brain, the current data indicate that it is most apparent among bisexual males. Sexing of their brains may involve several sexually dimorphic regions that are related in a continuous manner. Inferred cerebral feminization was more circumscribed among gay and heterosexual males, for whom childhood sex atypicality was most highly-distinguishing. Unspecified mechanisms responsible for homoeroticism in them may differ from those that produce same-sex attractions in bisexuals and thus have relatively little impact on other components of cerebral feminization.

Adolescent↗
PubMed2003

Left-handedness in asthmatic children.

Left-handedness has been associated with asthma and allergic disorders. The Geschwind-Behan-Galaburda (GBG) hypothesis could explain this association. In view of previous findings, we investigated the distribution of laterality scores among asthmatic children and controls aged 4-8 years old. Seventy families with asthmatic children were administered the International Study of Asthma and Allergy in Childhood (ISAAC) questionnaire and the Edinburgh Left-handedness Inventory. A sample of 70 families with non-asthmatic, healthy children was used as controls. The majority of children had mild asthma. Ambidexterity was the main feature in the asthmatic children. A statistically significant difference in the laterality quotient (LQ) distribution was found in the group of asthmatic children with allergic rhinitis (LQ mean value in the asthmatic children with allergic rhinitis: 42.85 vs. 79.50 in the rest of the asthmatic children). These results suggest that there is a tendency towards left-handedness in asthmatic children and lend support to the GBG hypothesis.

Asthma↗
PubMed1985

Handedness and sex differences in selective interference of verbal and spatial information.

The purpose of this experiment was to investigate handedness and sex differences with regard to the way verbal and spatial information is coded in selective-interference tasks. Left- and right-handed males and females were required to recall both letters and their positions in a matrix under three different kinds of interpolated conditions: visual, auditory, and noninterpolated activities. The results indicated that the selective-interference effect differed in right- and left-handers, whereas there were no differences by sex. Identity information had a dual encoding for both handedness groups, but it was relatively more biased toward visual encoding in left-handers than in right-handers; position information, however, was predominantly visually encoded--and to the same extent--in both handedness groups. These findings were interpreted as supporting the view that the differences in coding manner of right- and left-handers are related to differences in their hemispheric specialization.

Adult↗
PubMed2000

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.

Brain↗
PubMed2001

Is the handedness gene on the X chromosome? Comment on Jones and Martin (2000).

G. V. Jones and M. Martin (2000) argued, contrary to M. C. Corballis (1997), that a gene for handedness might plausibly be located in homologous, noncombining regions of the X and Y chromosomes. The specific model they proposed is unlikely to be correct, but a case can be made for an X-linked gene that has no homologue on the Y chromosome and that is subjected to X-inactivation in females. An X-linked gene predicts no overall sex difference in the incidence of left-handedness; the slight preponderance of left-handers among males might then be attributed to a higher incidence of pathologically induced left-handedness.

Female↗
PubMed2003

Comparative assessment of handedness for a coordinated bimanual task in chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus).

Hand preferences for a coordinated bimanual task were assessed in a sample of 31 captive gorillas (Gorilla gorilla) and 19 captive orangutans (Pongo pygmaeus) and were compared with chimpanzee (Pan troglodytes) hand preferences in subjects that were matched on the basis of age, sex, and rearing history. The task required that the apes remove food from the inside edges of a symmetrical polyvinyl chloride pipe presented to them in their home cages. The results indicate significant species differences with chimpanzees showing population-level right-handedness and orangutans showing population-level left-handedness. The gorillas showed a nonsignificant trend toward right-handedness. The results are discussed in terms of possible ecological or biomechanical factors that may influence hand preferences in different ape species.

Animals↗
PubMed2005

Factors influencing the prevalence and handedness for throwing in captive chimpanzees (Pan troglodytes).

Humans throw right-handed, and it has been suggested that the neurophysiological demands of aimed throwing may have served as a precursor to the evolution of left hemisphere specialization for linguistic functions. Although there are descriptions of throwing by wild and captive chimpanzees (Pan troglodytes), systematic observations of aimed throwing and handedness have not been reported. In this article, evidence of population-level right-handedness for throwing is reported in 2 samples of captive chimpanzees. It is further reported that right-handed throwing is more pronounced than other measures of handedness in captive chimpanzees. The implications of these findings are discussed in the context of theories relating throwing to the evolution of lateralization for language functions.

Animals↗
PubMed1991

Sex, handedness, mathematical ability, and biological causation.

An important part of Benbow's (1988) assertion that sex differences in mathematical ability are primarily due to biological factors is the link between a trait that is assumed to reflect differences in brain organization (left-handedness) and mathematical giftedness. It is shown that the link between mathematical giftedness and an increased prevalence of left-handedness is not convincing. However, Benbow's (1986) data do show a convincing link between strong right-handedness and the lack of mathematical giftedness, in agreement with Annett and Manning's (1990a, 1990b) recent work.

Aptitude↗
PubMedDate not supplied

Determination of twist and handedness of a 39-base pair segment of DNA in solution.

For DNA in solution, there have been two methods for measuring the helical periodicity. One method examines the ladder of discrete bands formed in the electrophoretic pattern of supercoiled DNA. Such a ladder is assumed to reflect the set of differently linked covalently closed molecules. The other method measures the lengths of partial nuclease digestions of DNA segments affixed to flat surfaces. Neither method, however, is able to measure the absolute handedness. X-ray diffraction of DNA oligonucleotides can determine the handedness, but the DNA must necessarily be crystallized. We have developed a new method for determining the helical parameters of a segment of DNA in solution. It is the first non-crystallographic method that can directly determine both the helical periodicity and the absolute handedness of DNA. The results obtained using this method are consistent with the classical Watson-Crick right-handed double helical model.

DNA↗
PubMed2003

Parametric and nonparametric genome scan analyses for human handedness.

We have performed a genome scan using 25 nuclear families consisting of right-handed parents with at least two left-handed children. Handedness was assessed as a qualitative trait using a laterality quotient. Laterality quotients indicate the direction of handedness, which is hand preference for performing unimanual tasks. Both parametric and nonparametric linkage analyses were applied. The parametric analysis using the single-locus genetic model of Klar resulted in four different regions with LOD scores higher than 1. The region on chromosome 10q26 gave a suggestive LOD score of 2.02 at a recombination fraction of 0.05. Nonparametric analysis gave an NPL score for this region of 2.16. However, further fine mapping of the region on chromosome 10q26 failed to obtain a higher LOD score. These results suggest that handedness is a human quantitative trait locus and that the proposed non-Mendelian monogenic models are incorrect.

Adult↗
PubMed1994

Handedness and headache.

A California handedness study involved 199 male and 74 female cluster headache sufferers as well as 477 migraineurs. Earlier reported data indicated that cluster headache patients had a left-handedness prevalence of over 15%. With the current data the prevalence in males was 11.0% and in females, 8.2%. The corresponding migraine figures were 11.8% and 8.1%. The cluster and migraine headache groups did not differ significantly from each other or from the expected 10% frequency of left-handedness in either sex.

Adult↗
PubMed1997

Motor performance and handedness in children with developmental language disorder.

Developmental language disorder (DLD) is diagnosed when there is a failure of normal language development in a child with normal nonverbal intelligence. The discussion about additional or causal deficits is controversial. In this study a computer-based motor performance series with a tapping, aiming and pegboard movement task and an additional paper-pencil handedness test were applied to a group of children with DLD of the phonologic-syntactic subtype and with normal nonverbal intelligence to describe the additional motor problems. Furthermore we examined whether our DLD children showed a different handedness. Tapping and pegboard with both hands were significantly impaired in our DLD children. Overall our DLD children did not show a different handedness than the control group.

Age Factors↗
PubMed1997

Functional activation in motor cortex reflects the direction and the degree of handedness.

Handedness is the clearest example of behavioral lateralization in humans. It is not known whether the obvious asymmetry manifested by hand preference is associated with similar asymmetry in brain activation during movement. We examined the functional activation in cortical motor areas during movement of the dominant and nondominant hand in groups of right-handed and left-handed subjects and found that use of the dominant hand was associated with a greater volume of activation in the contralateral motor cortex. Furthermore, there was a separate relation between the degree of handedness and the extent of functional lateralization in the motor cortex. The patterns of functional activation associated with the direction and degree of handedness suggest that these aspects are independent and are coded separately in the brain.

Adult↗
PubMed2004

Effect of handedness on learning subgingival scaling with curettes: a study on manikins.

The aim of the present study was to evaluate the influence of systematic manikin-head training and the effectiveness of subgingival scaling applied with hand instruments (curettes) by right- and left-handed dental students on dental chairs (traditional) designed for right-handers. A questionnaire focusing on handedness was administered to 69 voluntary dental students in the third class at the School of Dentistry during pre-participation examination. Handedness was assessed using the Turkish version of the Edinburgh Handedness Inventory. Then, 18 dental students were specially selected in 2 equal groups according to hand preference: consistent right-handers with Geschwind Scores of +100 (5 female and 4 male) and consistent left-handers with Geschwind Scores of -100 (5 female and 4 male). These two untrained dental student groups received 10 weeks manikin-head training. Subgingival scaling was performed with hand instruments (Gracey curettes) in manikin-head mounted on right-sided dental chairs. At 6 test days each dental student had to instrument 12 test teeth. Effectiveness of subgingival scaling was evaluated by adoption of a grading system. This system had scores from 0 to 3 and was defined by illustrated and described criteria. Statistical analysis was carried out with SPSS. Two groups were statistically compared on all test days. The yet-untrained left-handed dental students begin with a relatively high the mean score of 2.25, compared to the yet-trained right-handed dental students with 1.93, which was statistically significant (p > .05). The right-handed dental students reached the mean score of 0.53, whereas the left-handed dental students reached the mean score of 0.87 on test day 6. Significant differences in the mean scores were found between the two groups for overall surfaces (p < .05), the distal surfaces (p < .01), lingual surfaces (p < .01), and each group of teeth (p < .05). But there was no statistically significant difference between the 2 groups of students on all test day, except for test day 3 in terms of the mean scores for the facial and mesial surfaces (p > .05). Learning success was observed a high level in both groups through systematical training (p < .0001). The present study has documented that the left-handed dental students were less successful than the right-handed dental students in subgingival scaling, except for mesial and facial surfaces. However although training on right-sided chairs, they were quite similar to their right-handed counterparts in terms of learning success.

Adult↗