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Suspected autoimmune disorders and left-handedness: evidence from individuals with diabetes. Crohn's disease and ulcerative colitis.

This study tested the theory that left-handedness is associated with certain disorders that may have an autoimmune aetiology. To accomplish this, we compared the handedness patterns of people with either Type I or Type II diabetes, Crohn's disease, or ulcerative colitis with a normal control group. Consistent with earlier findings, a significantly higher incidence of left-handedness was observed in people with either Crohn's disease or ulcerative colitis. In addition, there was evidence that males with Type I diabetes were more likely to be left-handed than males with Type II diabetes.

Adolescent↗

Academic discipline, handedness and immune disorders.

Much debate has surrounded the relative contribution of genetic inheritance and environment to human intelligence. In addition, fetal hormones may influence brain development and affect the qualitative nature of intellectual skills. Geschwind and Behan, Proc. Natn. Acad. Sci. 79, 5097-5100, 1982, have suggested that such hormones may also influence both the development of handedness and the development of the immune system. Members of the faculty of the University of Oxford participated in a survey investigating field of study; handedness and immune disorders. Even amongst right-handers, mathematical academics are significantly more susceptible to rare immune disorders and four times likely as verbal academics, to have suffered from a language related problem in childhood. In contrast to previous suggestions, the incidence of left-handedness is not found to be high amongst pure mathematicians but is significantly higher amongst scientists using mathematical applications.

Adult↗

Left-handedness and myasthenia gravis.

In two separate studies comparing the handedness of patients suffering from myasthenia gravis with matched controls, no evidence was found to support the Geschwind Behan hypothesis of an association between autoimmune disease and left-handedness. Counter to prediction both studies found marginally lower incidences of left-handedness in myasthenics, and when combined with the similar result of Cosi et al. (Cortex 24, 573-577, 1988) the difference was highly statistically significant. The personality of myasthenics, as assessed by the Eysenck Personality Questionnaire (EPQ), and in particular the psychoticism scale, which has been postulated to be related to androgen levels, was not significantly different from controls. However, assessment of sex-roles using the Bem Sex Role Inventory suggested that female myasthenics were more masculine than controls.

Adult↗

Handedness in the human fetus.

The developmental origins of behavioural asymmetries, in particular handedness, have aroused considerable interest and debate. Until now such behavioural asymmetries have only been reported after birth. Here we report the existence of handedness before birth, expressed in terms of thumb-sucking by the fetus. Ultrasound observations of fetuses from 15 weeks to term revealed a marked bias for sucking the thumb of the right hand. This preference appears to be maintained throughout pregnancy, is unrelated to fetal position in utero but correlates with head position preference in the supine newborn. The findings indicate that handedness is present prior to birth and the implications of this for the development of laterality are discussed.

Female↗

Career choice and handedness: a survey among university applicants.

By means of the Edinburgh Handedness Inventory the patterns of handedness were studied in 16,590 applicant students to several professional courses in a Brazilian university. The distributions of the laterality quotient (LQ) were different for male and female students, with more left-handers found among the males. The LQ's distributions were different for applicants to distinct courses or to blocks of related occupations. However, no differences were observed between left- and right-handers when each sex was studied separately. No statistically significant differences in handedness were found among the students of different courses that were accepted by the university.

Adolescent↗

Handedness in native Amazonians.

A sample of 65 Tucano adolescents living in the Amazon region of Colombia were administered a 26-item handedness questionnaire. All subjects were right-handed. A factor analysis of the data indicated a factor structure rather different from that seen in North Americans, although both skilled and unskilled handedness factors were seen. Other factors related to specific tool use and to strength. These data indicate that positive reinforcement for right-hand use can modify patterns of handedness, and may well alter the relations among different items. The data suggest that hand preference can be modified through positive reinforcement at an appropriate age, and that hand preference is the precursor of skill differences rather than vice versa.

Adolescent↗

Functional brain organization, handedness, and immune vulnerability in musicians and non-musicians.

In the current investigation an approach has been made to explore possible relations between musical talent, left-handedness, anomalous dominance for verbal materials, and immune vulnerability. Fifty-one young adult musicians and non-musicians were tested with Wing's Standardized Tests of Musical Intelligence, with a handedness questionnaire, a dichotic listening task, and with a questionnaire assessing asthma/allergies, migraine and myopia. In addition, IgE, Ig total, beta-endorphin, testosterone, and estradiol were measured in blood serum. Musical talent was related to left-handedness and to anomalous dominance; immune vulnerability was found in female musicians, and in subjects with reversed dominance for language functions as well as in male left-handers, independently of musical talent.

Adolescent↗

Left-handedness and old age: do left-handers die earlier?

Data are presented on the prevalence of current left-handedness and prior left-handedness (switched) in 2787 subjects from 21 to 101 years of age. In addition, data on sex differences, familial sinistrality, hand posture when writing, and education were recorded. Two hypotheses were tested. The elimination hypothesis states that reduced frequency of left-handers in old age is due to reduced longevity. The modification hypothesis states that differences in the number of left-handers between older and younger persons are due to changing patterns of social norms. The results showed a decreasing prevalence of left-handedness across the age span, with 15.22% in the youngest group (21-30 years), but only 1.67% in subjects older than 80 years. There was however a corresponding increase in the number of subjects who had switched hand for writing, 2.69% in the youngest group to 6.75% in subjects 80 years and above. This supports the modification hypothesis and questions the elimination hypothesis. However, the mean percent score was still lower in subjects above compared to below age 40 after correction for hand switching. Thus, although changes in social norms towards left-handers seem to be the most likely explanation, we have not empirically disproved the elimination hypothesis.

Adult↗

Handedness and sex of children with developmental language disorders.

The handedness and sex of 4- and 5-year-old children with developmental language disorders were studied through a comparison of language disordered children and a normal control group and through a comparison of six linguistically homogeneous subgroups of language disordered children. Differences between the handedness of a generalized language disordered group and a normal control group were not found, possibly due to the multiple etiologies of developmental language disorders. Children with severe language disorders, however, were non-right-handed more often than children with mild language disorders. Furthermore, certain types of linguistic deficits were associated with non-right-handedness, whereas age and cognitive abilities were not. Males were more often language disordered than females; however, sex ratios did not significantly differ among the subgroups, possibly due to the small number of language disordered females in this study. Implications for cerebral laterality in developmental language disorders are discussed.

Child, Preschool↗

Handedness patterns in deaf persons.

The handedness patterns of 226 deaf high-school and college students were compared to those of 210 college students with normal hearing. Both groups evidenced many more right-handed than left-handed members, as determined by responses to a hand preference questionnaire and performance on an activity test battery. There was, however, a significantly higher incidence of left-handedness among the deaf subjects than among the hearing. Moreover, the left-handed deaf students were found to be less likely to have deaf relatives, and to have been introduced to sign language later in their development than the deaf student population as a whole. These findings were interpreted as showing that age of acquisition of language was related to the development of handedness patterns, whereas auditory processing experience probably was not.

Auditory Perception↗

Subject knowledge of the experimenter's interest in handedness and familial sinistrality variables and laterality test outcomes.

We investigated the possible influence of common "demand characteristics" on the results on behavioral language laterality tasks. The demand characteristics were (1) whether Ss were or were not recruited for study according to their handedness, and (2) whether a detailed familial sinistrality inquiry was conducted before or after the tasks. Tasks were the Dichotic Consonant Vowel Task (DCVT) and the Bilateral Object Naming Latency Task (BONLT). Results showed no effect of demand characteristics on the BONLT. On the DCVT, however, prior inquiry regarding familial sinistrality was associated with significantly reduced right ear advantages (REAs). Interactions showed that the greatest reduction in REAs occurred in Ss with left-handedness in their families, who were asked about familial sinistrality prior to the tasks, who took the DCVT after the BONLT, and who were also recruited by handedness. Results, though generally reassuring regarding the robustness of the tasks against these sources of bias, raise some cautions for the DCVT.

Dichotic Listening Tests↗

The influence of gender, handedness, and performance level on specialized cognitive functioning.

Individual differences in performance on neuropsychological tests were analyzed across age (prepubertal to adult), gender, and handedness groups and examined for performance level as a moderating variable. No differences were observed for the factor structure of these tests across ages and between genders, suggesting similar cognitive structures among these groups. Significant differences in performance were observed between males and females and, to a lesser extent, between right and left handers. Of interest, were significant Gender x Handedness and Gender x Handedness x Level (of performance) interactions seen especially in the older (postpubertal and adult) subjects. High performing, right handed males and left handed females performed better on visuospatial tasks while left handed males and right handed females performed better on verbosequential tasks.

Adolescent↗

Bilateral electrodermal activity as a function of hemisphere-specific stimulation, hand preference, sex and familial handedness.

UNLABELLED: The effects of unilateral stimulation on bilaterally recorded electrodermal activity are not well understood. Factors that may contribute to bilateral response differentiation under conditions of unilateral stimulation include preferred hand, sex and familial handedness. To assess the effects of these factors, 64 subjects were each assigned to one of four cells defined by sex and preferred hand. Each subject received a counterbalanced series of 31 slides depicting objects spatially and intended to activate the right hemisphere and 31 slides depicting objects spatially and intended to activate the left hemisphere. Each condition was followed by a blank slide. Results showed smaller mean nonspecific responses on the hand contralateral to the hemisphere for which stimulation was intended. This supports the hypothesis that a contralateral inhibitory process underlies electrodermal responsiveness. Further results showed that the effects of unilateral stimulation on bilaterally differentiated electrodermal activity are mediated by familial handedness and sex. DESCRIPTORS: hemispheric processes, bilateral EDA, sex, familial handedness, preferred hand.

Adult↗

A new method of administering the Grooved Pegboard Test: performance as a function of handedness and sex.

The purpose of the present study was twofold: first to examine the influences of sex and handedness on manual performance on the Grooved Pegboard Test; and secondly to provide normative data for two versions (Place and Remove tasks) of the Grooved Pegboard Test, as previous work (Bryden & Roy, 1999) had suggested that the Remove task of the Grooved pegboard may provide a purer measure of motor speed of the two hands than the standard administration of the Grooved Pegboard Test. One hundred and fifty-three (47 males and 106 females) participants completed the Grooved Pegboard Test. Individuals performed the standard version of the Grooved Pegboard Test (Place task) and a novel version of the test (Remove task). In the standard version, participants were timed on their speed for placing the pegs, while in the novel version they were timed on their speed for removing the pegs. Results confirmed previously noted hand and sex differences in the Place task of the Grooved Pegboard Test, as well as the lack of effect of handedness on performance (Bornstein, 1995; Ruff & Parker, 1993). Significant performance differences between the hands were also noted for the Remove task. Findings also indicated that the Remove task was sensitive to sex and handedness effects.

Adolescent↗

Effects of handedness and gender on macro- and microstructure of the corpus callosum and its subregions: a combined high-resolution and diffusion-tensor MRI study.

The corpus callosum (CC) represents the major commissural tract connecting the two cerebral hemispheres and is supposed to play crucial integrative role in functional hemispheric specialization. The present study examined whether interindividual variations in macro- and microstructure of the human CC are associated with handedness and gender. Therefore, a combined diffusion-tensor (DTI) and high-resolution morphological MRI study was performed on 34 right- and 33 left-handed subjects of both sexes. The mid-sagittal surface areas and quantitative measures of molecular diffusion (relative anisotropy, mean diffusion) of the total CC and its subregions (genu, truncus, posterior third) were determined. Analysis revealed a larger total callosal area in right- as compared to left-handed subjects and in males as compared to females. Throughout all callosal subregions, anisotropy was found to be increased in left-handed as well as in male subjects, while the mean diffusion was diminished only in left-handers. For the posterior third of the CC, a significant negative correlation (r=-0.34) between anisotropy and area was detected in right-handed subjects. Summarized, significant alterations in the molecular diffusion and in the size of the CC with respect to gender and handedness were revealed in the present study. These findings can be interpreted as handedness- and gender-related differences in macro- and microstructure of the callosal pathways. It was demonstrated that the inspection of the callosal microstructure using DTI yields empirical evidence on interhemispheric connectivity that goes well beyond the information revealed by anatomical measurements alone. Thus, DTI has proven to be a useful additional method in cognitive neuroscience.

Adult↗

Handedness and the fringe of consciousness: strong handers ruminate while mixed handers self-reflect.

Previous research found that mixed handers (i.e., those that are more ambidextrous) were more likely than strong handers to update their beliefs (Niebauer, Aselage, & Schutte, 2002). It was assumed that this was due to greater degrees of communication between the two cerebral hemispheres in mixed handers. Niebauer and Garvey (2004) made connections between this model of updating beliefs and metacognitive processing. The current work proposes that variations in interhemispheric interaction (as measured by degree of handedness) contribute to differences in consciousness, specifically when consciousness is used in rumination versus the metacognitive task of self-reflection. Using the Rumination-Reflection Questionnaire (Trapnell & Campbell, 1999), predictions were supported such that strong handedness was associated with self-rumination; whereas, mixed handedness was associated with increased self-reflection p values<.01, (N=255). James's (1890) concept of the "fringe of consciousness" is used to make connections between metacognition, updating beliefs, and self-reflection. Several studies are reviewed suggesting that mixed handers experience fringe consciousness to a greater degree than strong handers.

Adult↗

The effect of handedness on cortical motor activation during simple bilateral movements.

The neuronal correlates of handedness are still poorly understood. Here we used event-related functional magnetic resonance imaging to investigate the impact of handedness on neuronal activation of the primary sensorimotor cortex, supplementary motor area and dorsal premotor cortex during simple unilateral and bilateral finger movements. In 16 right-handed and 16 left-handed individuals, we mapped changes in regional neuronal activity while participants responded to four symbolic cues presented in a pseudorandom order. According to pre-specified cues, they pressed a button with their right, left or both index fingers or withheld a response. For unilateral right index finger button presses, reaction times, motor and premotor activity were the same for both right- and left-handers. Compared with right-handers, left-handers had shorter reaction times with unilateral left index finger button presses, along with greater activation of the supplementary motor area and right frontal opercular cortex. Simultaneous bilateral compared with unilateral button presses led to a relative increase of activity in the right and left dorsal premotor cortex and the right primary sensorimotor cortex in right but not left-handers. Neither right nor left-handers showed any tendency during bilateral button presses towards faster responses with the dominant hand and the reaction times were equal in the two groups. Therefore, we conclude that the relative increase of activity in dorsal premotor and right primary sensorimotor cortices in right-handers represents a genuine difference in bimanual motor control related to handedness.

Adult↗

Prenatal thumb sucking is related to postnatal handedness.

This study followed-up 75 individuals who were observed sucking their thumb as fetuses and examined their handedness, assessed by a modified version of the Edinburgh Handedness Inventory, at 10-12 years of age. Of 60 right-handed fetuses, all were right-handed postnatally; 10 of 15 left-handed fetuses were left-handed and five right-handed. Male left thumb sucking fetuses were more likely to be right-handed children than females. The study indicates that the prenatal exhibition of lateralised motor behaviour, in this case thumb sucking, is indeed related to postnatal handedness, perhaps more strongly for right 'handed' fetuses than left 'handed' fetuses.

Child↗