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PubMed2006

Further evidence of an association between handedness and neuroanatomical asymmetries in the primary motor cortex of chimpanzees (Pan troglodytes).

The neurobiology of handedness is still poorly understood in nonhuman primates. Recently, an association between hand preference and precentral gyrus morphology in chimpanzees was reported. The aim of this study was to further evaluate the association between handedness and asymmetries in the precentral gyrus of chimpanzees (Pan troglodytes) and to evaluate the association between hand preference and brain asymmetry using a different approach to the classification of handedness in chimpanzees. The overall results suggest that differences in handedness groups are specific to a region of the precentral gyrus commonly known as the "knob" and that subjects that show different hand preferences differ in brain asymmetries for specific regions of the primary motor cortex. Moreover, using a continuous scale of measurement rather than discrete classification of handedness, significant associations were found between hand use and asymmetries within the precentral gyrus.

Animals↗
PubMed1991

Left-handedness, homosexuality, HIV infection and AIDS.

Left-handedness was assessed in a large sample of male homosexuals and male and female heterosexuals, some of whom had been tested for HIV infection, and others of whom had AIDS. No association was found between left-handedness and homosexuality, although there was an excess of left-handers in subjects who had been tested for HIV infection (irrespective of whether the test was negative or positive). This result can be interpreted in three possible ways: as a response bias on the part of left-handers who were aware of the Geschwind hypothesis that left-handedness may confer a vulnerability to AIDS; as due to left-handedness being associated with AIDS infection and the incidence in AIDS patients being artefactually low due to an excess mortality in left-handed AIDS patients; and as left-handers showing both an increased vulnerability of HIV infection and a reduced likelihood of progression of HIV infection into AIDS. Our data are unable to distinguish between these hypotheses. Left-handedness was not associated with any of seventeen specific conditions, including migraine, dyslexia and stuttering.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Assessment of handedness using a digitizing tablet: a new method.

The assessment of handedness is of interest in some psychiatric populations, above all in schizophrenic patients, because there may be a relationship between neurodevelopmental, hemispheric damage and psychiatric disease processes (Crow TJ. Schizophrenia Bulletin 1990;16:433-443; Tyler M, Diamond J, Lewis S. Schizophrenia Research 1995;18:37-41). Various methods to assess handedness have been proposed. In order to detect the most precise instrument for the assessment of handedness, two different measures, a questionnaire and a computational procedure for movement analysis, were compared in a group of healthy subjects. The ability of the methods to discriminate not only between the groups of right-handers (n=12) and left-handers (n=23), but also between left-handers trained in school to use the non-dominant right hand ('inconsistent' left-handers; n=11) and those allowed to use their left hand for writing ('consistent' left-handers; n=12) was investigated. For future investigations, our main concern was to determine if one method had superiority over the other. The results revealed that the Edinburgh Handedness Inventory (EHI) distinguishes just as well as the computational method between right-handers and non-right-handers. However, more precise discrimination between the subgroups of 'consistent' and 'inconsistent' left-handers is possible using digitized analysis of hand-motor performance. According to our results handedness should be assessed not only with the EHI, but also with the computer-aided analysis of hand-movements.

Adult↗
PubMed2002

Early life environment modulates 'handedness' in rats.

Right handedness is one of the most prominent markers of human functional brain asymmetry. Deviation from this norm appears to be associated with certain developmental disorders. While many studies have dealt with the genetic contribution to the determination of handedness, few have examined whether environmental factors that are subtler than forced hand switching can modulate the development of handedness. In this study, we exposed rats to a novel environment for 3 min daily during their first 3 weeks of life and found that their paw preferences during both infancy and adulthood showed a leftward shift compared with the controls. This result suggests that 'handedness' can be modified by rather subtle early environmental manipulation. Since exposure to a novel environment does not involve a direct asymmetric activation of the sensory--motor system underlying paw-use, mechanisms beyond this paw-specific system must exist to mediate the observed modulation of 'handedness'.

Animals↗
PubMed2003

Familial handedness and spatial ability: a study with Chinese students aged 14-24.

This study tested Annett's right-shift theory on spatial ability with two samples from China. The Vandenberg Mental Rotation Test (MRT), Edinburgh Handedness Inventory, and Family Handedness Questionnaire were administered to 266 high school students and 297 undergraduates. We found very few r++ or r-- among Chinese students. Most Chinese are either moderately right-handed or ambidextrous. Consistent with Casey's finding, we found using different methods to classify handedness leads to different conclusions. However, we did not find the effect of familial handedness that Casey found. Visual strategy is related to success on the MRT but handedness is not.

Adolescent↗
PubMed2003

Psychological factors in pregnancy and mixed-handedness in the offspring.

Animal studies suggest that psychological factors may interfere with the development of brain asymmetry during gestation. We evaluated whether psychological exposure in pregnancy was associated with mixed-handedness in the offspring. In a follow-up design study, 824 Danish-speaking women with singleton pregnancies provided information on psychological distress and the occurrence of life events in the early second and third trimesters of pregnancy. Handedness of the children was based on maternal reports when the children were 3 years of age. Among the 419 males and 405 females, 7% and 5% respectively were mixed-handed whereas mixed-handedness was found in 3% of the parents. Psychological distress in the third trimester as well as higher levels of stressful life events were related to a higher prevalence of mixed-handedness in the offspring. About 16% of the women reported more than one life event in the third trimester of pregnancy and among the offspring of these women 11% were mixed-handed (odds ratio = 2.3; 95% confidence interval 1.2 to 4.4). Women who at the same time reported a high level of distress and stressful life events, had a three- to four-fold higher prevalence of mixed-handedness in their offspring.

Adult↗
PubMed1989

Is there atypical handedness in schizophrenia?

Ninety-three schizophrenic patients and 105 normal controls were tested in a single session on an 8-item repeat-administration handedness test. The schizophrenic group, in contrast to the normal controls, showed a shift in the distribution away from right-handedness, which was due to an increase in the proportion of mixed-handers. Additional analyses revealed that the increase in mixed-handedness was largely due to an increase of within-item variability in the schizophrenic group, which we refer to as ambiguous handedness. Nearly 20% of the schizophrenic patients were inconsistent on 3 or more items compared with 3.8% of the normal controls. This increased incidence of atypical handedness is discussed within the context of disorders of attention and neurodevelopment.

Adult↗
PubMed2000

A note on Corballis (1997) and the genetics and evolution of handedness: developing a unified distributional model from the sex-chromosomes gene hypothesis.

A unified, quantitative model for sex, twin, parent, and grandparent influences on handedness is presented. Recent research modeling the evolutionary development of genetic mechanisms for the transmission of handedness on the basis of genotype fitness has appeared to lead to the conclusion that a handedness gene cannot be located on the sex chromosomes. It is shown in this article, however, that this conclusion is not of general validity. The sex-chromosomes hypothesis is developed further, and it is demonstrated that a wide-ranging, detailed, and parsimonious account of the distribution of handedness is obtained when left-handedness is assumed to be associated recessively, and with low penetrance, with genetic variation located on the X chromosome.

Female↗
PubMed2007

Extreme right-handedness, older brothers, and sexual orientation in men.

Two of the most consistent correlates of sexual orientation in men are handedness and fraternal birth order (i.e., number of older brothers). In the present study, the relationship among handedness, older brothers, and sexual orientation was studied in 4 samples of heterosexual and gay or bisexual men (N = 944). Unlike previous studies, which have only observed an increased rate of non-right-handedness in gay or bisexual men relative to heterosexual men, an elevated rate of extreme right-handedness was found in gay or bisexual men relative to heterosexual men. The results also demonstrated that older brothers moderate the relationship between handedness and sexual orientation. Specifically, older brothers increase the odds of being gay or bisexual in moderate right-handers only; in both non-right-handers and extreme right-handers, older brothers do not affect (or decrease) the odds of being gay or bisexual. The results have implications for an early neurodevelopmental origin to sexual orientation in men.

Birth Order↗
PubMed1988

Migraine and left-handedness: is there a connection?

In 1982, Geschwind and Behan reported an association between migraine headache and left-handedness. The present study was an attempt to test this hypothesis by comparing the frequency of left-handedness in migraine and tension headache patients at a headache center. Cluster headache cases were also included because Geschwind and Behan suspected that the association might be even stronger in this disorder. A special scoring method for handedness was devised by Geschwind and Behan to help identify a possible higher risk in mixed-handedness subjects. No significant associations emerged in any of these tests. A modest association of cluster headache and left-handedness disappeared when adjustment was made for the strong predilection of cluster headache for the male sex.

Adult↗
PubMed1999

Ultrasound during pregnancy and subsequent childhood non-right handedness: a meta-analysis.

OBJECTIVE: A possible association between ultrasound during pregnancy and subsequent non-right handedness among children has been suggested. The association has been reported to be stronger among boys. The aim of the present study was to explore this further through a meta-analysis of two follow-up studies of three randomized controlled trials of routine ultrasonography during pregnancy. DESIGN: Handedness was assessed through a questionnaire to the parents, and 4715 children at the age of 8-9 years were included in the meta-analysis. RESULTS: There was no statistically significant difference in the prevalence of non-right handedness between the ultrasound-screened children and the controls, but there was a statistically significant difference in a subgroup analysis among the boys. Exploratory analyses according to exposure or non-exposure indicated an even stronger association between ultrasound and non-right handedness. CONCLUSIONS: A conservative analytical approach indicates no association between ultrasound in utero and subsequent non-right handedness. The results from the exploratory analyses must be interpreted with caution. There is still a need for further research.

Adult↗
PubMed2003

Prevalence of left-handedness among patients with different respiratory diseases.

We investigated the prevalence of left-handedness among patients with different respiratory diseases. Hand preference was assessed using the modified Edinburg Handedness Inventory. There was a statistically significant decline in left-handedness with shortened life span in patients. Difference among the rates of left-handedness in different pulmonary diseases was significant. The rate of left-handedness was lowest in patients with chronic obstructive pulmonary disease (2.14%) and pneumonia (2.04%) and highest in patients with asthma (12.96%). The results suggest that left-handed subjects may be protected from certain pulmonary diseases while being more susceptible to others.

Adolescent↗
PubMed1997

Do anomalies of handedness exist in children with Fragile-X syndrome?

Hand preference and skill were assessed in 27 children with Fragile-X syndrome, 30 children with Down's Syndrome, and 29 normal developing children. Three separate and specific anomalies of handedness that have been reported in other learning-disordered groups were examined: increased incidence of left-handedness; ambiguous or inconsistent handedness; and preference-skill discordance. The results revealed no difference between the subject groups in the distribution of left-handedness or ambiguous handedness. The main differences was the percentage of children who were discordant for hand preference and hand skill. In the Fragile-X group 37% preferred to use their right hand but demonstrated no overall difference in skilled performance between the hands. In contrast, only 13% of children with Down's Syndrome and 17% of normal controls showed this pattern of hand discordance. The results are discussed in the context of past research that has shown a similar dissociation of preference and skill in children with autism.

Journal Article↗
PubMed2001

Genes for left-handedness: how to search for the needle in the haystack?

Although several genes that determine left-right asymmetry for structural syndromes such as situs inversus have been characterised in recent years (Supp, Witte, Potter, & Brueckner, 1997), there has been little progress in determining which genes or loci predispose to left-right handedness in humans. Linkage analysis has been used widely for the localisation of genes followed by their positional cloning. The complex genetics of handedness is one of the greatest problems for standard linkage analysis. Several genetic models have been proposed for the inheritance of handedness in humans. On the basis of these models, left-handedness can be considered a common single gene trait with a high gene frequency and a non-mendelian inheritance pattern. We report here a possible strategy, using these genetic models, that can be applied for the identification for genes determining handedness in humans.

Journal Article↗
PubMed2001

Inferring handedness from lithic evidence.

Until recently research into the origins of human handedness has been hampered by the lack of valid techniques for inferring handedness in pre-modern populations. A method developed by Toth for inferring handedness from lithic evidence, based on orientation of the cortex on lithic flakes, has produced promising results. However, this method is limited in applicability and has a variable signal to noise ratio. The authors describe a separate method, based on the orientation of the cone of percussion in lithic flakes, for inferring handedness from the lithic evidence. This method complements the cortex method. Some preliminary experimental evidence is presented which indicates that handedness can be inferred from lithic evidence using the cone of percussion method. Suggestions for further research are made.

Journal Article↗
PubMed2003

Left-handedness is correlated with CSF monoamine metabolite and plasma cortisol concentrations, and with impaired sociality, in free-ranging adult male rhesus macaques (Macaca mulatta).

In this research we examined biological and behavioural correlates of handedness in free-ranging adult male rhesus macaques (Macaca mulatta). Specifically, we examined relationships between handedness and cerebrospinal fluid (CSF) concentrations of the monoamine metabolites 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), plasma concentrations of the hormones cortisol and adrenocorticotropin (ACTH), and multiple indices of social behaviour, including occurrences of proximity to other animals, grooming, submission, and aggression. We determined handedness through systematic observation of animals reaching for food in their unrestricted home environment. The frequency of right- versus left-hand use was significantly positively correlated with CSF 5-HIAA, CSF MHPG, and plasma cortisol concentrations, and with social proximity and the frequency and duration of bouts in which animals received grooming. The frequency of right- versus left-hand use was significantly negatively correlated with the frequency of submissive behaviour, and with the frequency and intensity of bouts in which animals received aggression. We conclude that handedness is associated with an array of biological and behavioural processes in free-ranging adult male rhesus macaques and that left-handedness may be used to identify individuals at increased risk for impaired functioning of the serotonin, norepinephrine, and hypothalamic-pituitary-adrenal systems, and for social isolation and susceptibility to violent attack.

Journal Article↗
PubMed2003

Relationships between sulcal asymmetries and corpus callosum size: gender and handedness effects.

Magnetic resonance imaging was used to establish the presence and nature of relationships between sulcal asymmetries and mid-sagittal callosal size in neurologically intact subjects, and to determine the influences of sex and handedness. Against a background of long-standing disputes, effects of gender and handedness on callosal size, shape, and variability were additionally examined. Both positive and negative correlations between sulcal asymmetry and callosal size were observed, with effects influenced by sex and handedness. The direction of relationships, however, were dependent on the regional asymmetry measured and on whether real or absolute values were used to quantify sulcal asymmetries. Callosal measurements showed no significant effects of sex or handedness, although subtle differences in callosal shape were observed in anterior and posterior regions between males and females and surface variability was increased in males. Individual variations in callosal size appear to outrange any detectable divergences in size between groups. Relationships between sulcal asymmetries and callosal size, however, are influenced by both sex and handedness. Whether magnitudes of asymmetry are related to increases or decreases in callosal size appears dependent on the chosen indicators of asymmetry. It is an oversimplification, therefore, to assume a single relationship exists between cerebral asymmetries and callosal connections.

Adult↗
PubMed2000

Left-handedness in relation to breast cancer risk in postmenopausal women.

Breast cancer risk may be influenced by intrauterine exposure to steroid hormones. We evaluated left-handedness, a marker of intrauterine hormone exposure, in relation to breast cancer risk in our population-based, case-control study. Case women 50-79 years of age with a first diagnosis of invasive breast cancer were ascertained through statewide cancer registries in Wisconsin, Massachusetts, and New Hampshire. Control women were identified in each state through lists of licensed drivers (for ages 50-64) and Medicare beneficiaries (for ages 65-79), and selected at random to correspond with the age distribution of case women. Exposure information, including handedness, was obtained through a telephone interview. Our results indicated a modest association between left-handedness and breast cancer risk (OR = 1.42; 95% CI = 1.10-1.83). The effect of left-handedness was modified by age; we observed the greatest risk ratio in the oldest age group. Left-handedness was not associated with breast tumor laterality. Our results are consistent with the hypothesis that intrauterine hormone exposures play a role in the development of breast cancer.

Aged↗