Handedness and health: An examination of the association between different handedness classifications and health disorders

[The relationship between immunological and psychopathological characteristics in patients with focal epilepsy depending on the profile of interhemispheric asymmetry]

OBJECTIVE

To identify the possible influence of cellular immunity parameters and neurobiological variables (frequency of seizures of various semiotics and their severity) on comorbid psychopathological symptoms depending on the profile of interhemispheric asymmetry in patients with focal forms of epilepsy.

MATERIAL AND METHODS

The study included 92 patients with epilepsy (38 men, 54 women, mean age 38.7+8.45 years). Focal temporal lobe epilepsy was diagnosed in 36 patients, focal frontal lobe epilepsy in 16 patients, and temporal-frontal lobe epilepsy in 40 patients. For each type of seizure, severity was assessed according to the National Seizure Severity Scale (NHS3). The mental status of patients was assessed using the SCL-90 self-report questionnaire. The Annette scale was used to assess the profile of interhemispheric asymmetry. The number of different clusters of lymphocytes was studied, including the number of T-lymphocytes (CD3+), T-helpers (CD3+CD4+), T-cytotoxic (CD3+CD8+), T-NK (natural killers CD3+CD16+CD56+), B-lymphocytes (CD3-CD19+), as well as immunoregulatory index (CD4/CD8 ratio). In order to identify any possible relationships between neurobiological and immune variables, on the one hand, and the SCL-90 constructs, on the other hand, a separate correlation analysis of Spearman ranks within the left-handed group and the right-handed group was carried out.

RESULTS

We revealed the differences between groups of patients with epilepsy with right and left profiles of hemispheric asymmetry regarding the relationship between the frequency of seizures, their severity and accompanying psychopathological variables, on the one hand, and between immunity indices and psychopathological constructs, on the other hand. It has been established that neurobiological and immune variables in left-handers can determine the psychopathological structure of the comorbid mental disorder.

CONCLUSION

Prediction of concomitant psychopathological syndromes in patients with epilepsy on the basis of clinical data and data on immunity is quite possible, but only in left-handed patients.

Patient-Specific Characteristics Associated with Favorable Response to Vagus Nerve Stimulation

OBJECTIVE

The expansion in treatments for medically refractory epilepsy heightens the importance of identifying patients who are likely to benefit from vagus nerve stimulation (VNS). Here, we identify predictors with a positive VNS response.

METHODS

We present a retrospective analysis of 158 patients with medically refractory epilepsy. Patients were categorized as VNS responders or nonresponders. Baseline characteristics and time to VNS response were recorded. Univariate and multivariate Cox regression were used to identify predictors of response. Recursive partitioning analysis was used to identify likely VNS responders.

RESULTS

Eighty-nine (56.3%) patients achieved ≥50% seizure frequency reduction. Left-hand dominance (hazard ratio [HR] 1.703, P = 0.038), age at epilepsy onset ≥15 years (HR 2.029, P = 0.005), duration of epilepsy ≥8 years (HR 1.968, P = 0.007) and age at implantation ≥35 years (HR 1.809, P = 0.020), and baseline seizure frequency <5/month (HR 1.569, P = 0.044) were significant univariate predictors of VNS response. Following multivariate Cox regression, left-hand dominance, age at epilepsy onset ≥15 years, and duration of epilepsy ≥8 years remained significant. With recursive partitioning analysis, patients with either age at epilepsy onset ≥15 years, left-hand dominance, or baseline seizure frequency <5/month were stratified into Group A and had a 73.9% responder rate; the remaining patients stratified into Group B had a 43.8% responder rate.

CONCLUSIONS

Patients with age at epilepsy onset ≥15 years, left-hand dominance, or baseline seizure frequency <5/month are ideal candidates for VNS.

Sleep Behaviors and Handedness in Gifted and Non-Gifted Children

Patterns of sleep behaviors appear to differ across students with special needs including those classified with developmental disorders, attention-deficit/hyperactivity disorder, and autism. One understudied segment of the special needs population is that of gifted children, students who bring their own unique set of behavioral characteristics. In the present study, it was hypothesized that because of unique cognitive and socio-emotional intensities, gifted children would experience elevated levels of sleep disturbance in comparison to their non-gifted peers. Handedness was also surveyed for additional insight into cerebral organization. The study's participants were 35 gifted and 23 non-gifted students between the ages of 8-12. To measure sleep behaviors, data from the Child Sleep Habits Questionnaire (Abbreviated), Sleep Self-Report, and a sleep diary were collected. To assess handedness, the Edinburgh Handedness Inventory was administered. Results indicated that although gifted students did trend toward experiencing more sleep disturbance, when compared to non-gifted students, no significant differences were found in mean bedtime, hours slept, sleeping problems, or use of electronic devices before bedtime. In terms of handedness, gifted participants displayed more left-hand bias. Although no differences were found between sleep patterns of gifted vs. non-gifted children, this study adds to the limited evidential base on gifted children, handedness, and sleep. Additional research on sleep behaviors within this special needs cohort may be warranted.

No association between adult sex steroids and hand preference in humans

BACKGROUND

There is ongoing debate about the effects of hormones on the lateralization of the developing brain. In humans, there are conflicting theories of how testosterone during development should affect lateralization. Empirical studies linking prenatal and postnatal testosterone levels to hand preference (a proxy for lateralization) are similarly mixed. Links between hand preference and health may also suggest a mediating role of steroid hormones such as testosterone and estradiol. Studies to date of adult steroid hormones and handedness have been hindered by samples that contain small numbers of non-right-handers.

RESULTS

In the largest study of the phenomenon to date, I find that the testosterone (n = 7290) and estradiol (n = 3700) levels of left- and mixed-handed adults are no different to those of right-handers. All Bayesian 95% highest density intervals contained 0.

DISCUSSION AND CONCLUSIONS

The results have implications for studies that show elevated risk of hormonal-related mental and physical disorders in left-handed individuals.

Prevalence of Left-handedness in China 2011: Small-area Estimates

Nationally representative survey data and small-area estimation techniques are used to assess geographic prevalence of left-handedness in China 2011. Measures of individuals' handedness are self-reported dominant hand and hand grip strength, yielding four estimates of left-handed prevalence at the provincial level. These estimates concord with one another. There are several geographic clusters of high-prevalence rates of left-handers located in ethnic minority-designated autonomous areas or historically revolutionary base areas, which may reflect a deep-rooted sense of defiance to authorities and promote such cultural values as individual autonomy and equality among local people.

Lower birthweight and left-/mixed-handedness are associated with intensified age-related sex steroid decline in men. Findings from the Men's Health 40+ Study

In males, age‐related decline in free testosterone (T) and dehydroepiandrosterone (DHEA) by 2–3% per year has been reported. Estradiol (E2) and progesterone (P) seem to decrease as well, but to a lesser extent. Lower sex steroid levels in men have been related to physical and mental symptoms. Low birthweight and left‐/mixed‐handedness (L/MH) are indicators of an adverse fetal environment during pregnancy, and both have been linked to morbidity in later life. The aim of this study is to examine the relationship between lower birthweight as well as L/MH and age‐related sex steroid decline. In a cross‐sectional study design, saliva samples were collected under standardized conditions from healthy men for subsequent steroid hormone analysis using standard luminescence immunoassays. T (M = 67.57 pg/mL), DHEA (M = 247.91 pg/mL), E2 (M = 1.29 pg/mL), and P (M = 28.20 pg/mL) have been quantified leading to a final sample of 256 men providing complete data on sex hormones (M_Age=57.8; SD_Age = 10.8). Information on participants’ birthweight was obtained from birth reports (N = 134), and participants were asked about their handedness (right‐handed, left‐handed, mixed‐handed) (N = 256). Multivariate‐adjusted linear regression models relating each sex hormone individually and the principal component of declining steroid hormones (DSH)—an integrated hormonal parameter—with handedness and birthweight did not identify significant associations except for handedness and E2. Moderation analysis using robust regression accounting for bias due to influential data points detected a significant association between age and DSH for handedness (β = −0.0314, p = 0.040) but only a trend for birthweight (β = 0.0309, p = 0.073). For lower birthweight, a trend toward intensified age‐related sex steroid decline in men was observed, while for L/MH, a significant association with intensified age‐related sex steroid decline was identified. These results indicate that L/MH and potentially also lower birthweight might be considered as early risk factors for endocrine health in later life.

Motorische Entwicklung und Händigkeit in den ersten beiden Lebensjahren

Zusammenfassung. Der Zusammenhang von motorischer Entwicklung in den ersten beiden Lebensjahren und der Händigkeit von Kindern (N = 367) wurde untersucht. 18 motorische Meilensteine wurden erfasst, 14 betreffen die Grob- und vier die Handmotorik. Die Händigkeit wurde durch eine Befragung der Eltern zum Zeitpunkt des Erreichens des Meilensteins („Freies und sicheres Gehen“) ermittelt, den die Kinder im durchschnittlichen Alter von 14 Monaten bewältigten. 42.1 % der Kinder bevorzugten ihre rechte, 9.6 % ihre linke Hand, 32 % gebrauchten beide Hände gleich häufig. 16.4 % der Eltern konnten keine Angaben zur Händigkeit machen. Kinder, die bereits eine ausgeprägte Präferenz für die rechte Hand zeigten, bewältigten die meisten der Meilensteine früher als linkshändige und Kinder ohne Bevorzugung einer Hand. Kinder, deren Eltern keine Angabe zur Händigkeit machten, zeigten keine Nachteile gegenüber Rechtshändern. Unterschiede hinsichtlich der Entwicklung körperlicher Merkmale konnten zwischen den Gruppen nicht nachgewiesen werden. Der Anteil der Jungen unter den Linkshändern war deutlich höher als der der Mädchen. Mit Ausnahme des Meilensteins „Sitzen“ konnten keine Unterschiede im Erreichen der Meilensteine zwischen den Geschlechtern nachgewiesen werden.

Handedness in man: The energy availability hypothesis

More than 90% of the human species are right handed. Although outwardly our body appears symmetrical, a 50/50% lateralization in handedness never occurs. Neither have we seen more than 50% left handedness in any subset of the human population. By 12-15weeks of intrauterine life, as many as 6 times more fetuses are noted by ultrasound studies to be sucking on their right thumbs. Distinct difference in oxygenation leading to dissimilar energy availability between right and left subclavian arteries in place by week 9 of life may hold the clue to the lateralization of hand function and eventually, the same in the brain. We know there is a higher incidence of left handedness in males, twins, premature babies and those born to mothers who smoke. They may represent a subset with less distinct difference in oxygenation between the 2 subclavian arteries during the fetal stage. This hypothesis if correct not only closes the gap in understanding human handedness and lateralization but also opens a vista for new research to focus on in utero tissue energy availability and its impact on outcome in life.

More symmetrical children have faster and more consistent choice reaction times

Greater cognitive ability in childhood is associated with increased longevity, and speedier reaction time (RT) might account for much of this linkage. Greater bodily symmetry is linked to both higher cognitive test scores and faster RTs. It is possible, then, that differences in bodily system integrity indexed by symmetry may underlie the associations of RT and intelligence with increased longevity. However, RT and symmetry have seldom been examined in the same study, and never in children. Here, in 2 large samples aged 4 to 15 (combined n = 856), we found that more symmetrical children had significantly faster mean choice RT and less variability in RT. These associations of faster and less variable RT with greater symmetry early in life raise the possibility that the determinants of longevity in part originate in processes influencing bodily system integrity early in the life-course.

Impact of right-handedness on anaesthetic sensitivity, intra-operative awareness and postoperative mortality

Anatomical, neurological and behavioural research has suggested differences between the brains of right- and non-right-handed individuals, including differences in brain structure, electroencephalogram patterns, explicit memory and sleep architecture. Some studies have also found decreased longevity in left-handed individuals. We therefore aimed to determine whether handedness independently affects the relationship between volatile anaesthetic concentration and the bispectral index, the incidence of definite or possible intra-operative awareness with explicit recall, or postoperative mortality. We studied 5585 patients in this secondary analysis of data collected in a multicentre clinical trial. There were 4992 (89.4%) right-handed and 593 (10.6%) non-right-handed patients. Handedness was not associated with (a) an alteration in anaesthetic sensitivity in terms of the relationship between the bispectral index and volatile anaesthetic concentration (estimated effect on the regression relationship -0.52 parallel shift; 95% CI -1.27 to 0.23, p = 0.17); (b) the incidence of intra-operative awareness with 26/4992 (0.52%) right-handed vs 1/593 (0.17%) non-right-handed (difference = 0.35%; 95% CI -0.45 to 0.63%; p = 0.35); or (c) postoperative mortality rates (90-day relative risk for non-right-handedness 1.19, 95% CI 0.76-1.86; p = 0.45). Thus, no change in anaesthetic management is indicated for non-right-handed patients.

Hand preference, performance abilities, and hand selection in children

It is widely know that the pattern of human handedness is such that approximately 90% of the population is right handed with the remainder being left handed, at least in the adult population. What is less well understood is how handedness develops and at what age adult-like handedness patterns emerge. Quantified in terms of both preference and performance, a plethora of different behavioral assessments are currently in use with both children and adults. Handedness questionnaires are commonly used; however, these possess inherent limitations, considering their subjective nature. Hand performance measures have also been implemented; however, such tasks appear to measure different components of handedness. In addition to these traditional measures, handedness has been successfully assessed through observation of hand selection in reaching, which has proven to be a unique and effective manner in understanding the development of handedness in children. Research over the past several decades has demonstrated that young children display weak, inconsistent hand preference tendencies and are slower with both hands. Performance differences between the hands are larger for young children, and consistency improves with age. However, there remains some controversy surrounding the age at which hand preference and hand performance abilities can be considered fully developed. The following paper will provide a review of the literature pertaining to hand preference, performance abilities and hand selection in children in an attempt to ascertain the age at which adult-like patterns of hand preference and performance emerge.

Lack of association of handedness with inattention and hyperactivity symptoms in ADHD

OBJECTIVE

Findings about the association of left-handedness and ADHD are inconsistent. While abnormal brain laterality is reported in children with ADHD, it is unclear if hand preference is associated with ADHD, severity symptoms, age, gender, comorbid psychiatric problems, or parental characteristics.

METHOD

Subjects were 520 boys and girls with a mean age of 9.04 (2.3) years. Only four children were with mixed-handedness. ADHD was diagnosed according to clinical assessment using accepted diagnostic criteria. In addition to the demographic characteristics and hand-use preference, inattention severity, hyperactivity severity, oppositional behavior symptoms, anxiety symptoms, and developmental coordination problems were assessed.

RESULTS

A total of 87.4% were right handed. A total of 12.6% were left handed. Left- or right-hand preference was not associated with age, gender, inattentiveness score, hyperactivity-impulsivity score, comorbid psychiatric problems, developmental coordination problems score, or parental characteristics.

CONCLUSION

Left handedness is not associated with higher parent-reported inattentiveness or hyperactivity. Hand-use preference is not gender related in ADHD.

Left-handedness in professional and amateur tennis

Negative frequency-dependent effects rather than innate predispositions may provide left-handers with an advantage in one-on-one fighting situations. Support mainly comes from cross-sectional studies which found significantly enhanced left-hander frequencies among elite athletes exclusively in interactive sports such as baseball, cricket, fencing and tennis. Since professional athletes' training regimes continuously improve, however, an important unsolved question is whether the left-handers' advantage in individual sports like tennis persists over time. To this end, we longitudinally tracked left-hander frequencies in year-end world rankings (men: 1973-2011, ladies: 1975-2011) and at Grand Slam tournaments (1968-2011) in male and female tennis professionals. Here we show that the positive impact of left-handed performance on high achievement in elite tennis was moderate and decreased in male professionals over time and was almost absent in female professionals. For both sexes, left-hander frequencies among year-end top 10 players linearly decreased over the period considered. Moreover, left-handedness was, however, no longer seems associated with higher probability of attaining high year-end world ranking position in male professionals. In contrast, cross-sectional data on left-hander frequencies in male and female amateur players suggest that a left-handers' advantage may still occur on lower performance levels. Collectively, our data is in accordance with the frequency-dependent hypothesis since reduced experience with left-handers in tennis is likely to be compensated by players' professionalism.

Left-handedness is statistically linked to lifetime experimentation with illicit drugs

Handedness has been linked to an enhanced risk of alcohol abuse, while less is known about other drugs. A convenience sample of 1004 male and female Italian participants (females=58%) from the general community (18 to 65 years old: average age = 30; standard deviation = 10, median = 25) was asked about: handedness (preference in writing); lifetime use of alcohol, tobacco, and illicit drugs; levels of psychological distress, as measured by the General Health Questionnaire (GHQ); and levels of delusion proneness, as measured by the Peters et al. Delusions Inventory (PDI). Overall, 92 individuals (9.2%) were classified as left-handed, with no significant difference reported among genders. Lifetime use of illicit drugs, primarily cannabis, was reported by 20% of the sample. In a multiple logistic regression analysis, after taking into account sex, age, and caseness on GHQ and PDI, left-handed people in the sample were statistically more likely to report lifetime experimentation with heroin, ecstasy/amphetamine, and, marginally, hallucinogens, but not alcohol or tobacco. Different mechanisms might contribute to an explanation of greater lifetime experimentation with some illicit drugs among left-handed people as compared to right-handed people. However, replications with clinical samples are necessary before any definitive statements can be made.

Brain asymmetry, immunity, handedness

The principle of symmetry-asymmetry is widely presented in the structural and functional organization of the nonliving and living nature. One of the most complex manifestations of this principle is the left-right asymmetry of the human brain. The present review summarizes previous and contemporary literary data regarding the role of brain asymmetry in neuroimmunomodulation. Some handedness-related peculiarities are outlined additionally. Brain asymmetry is considered to be imprinted in the formation and regulation of the individual’s responses and relationships at an immunological level with the external and internal environment. The assumptions that the hemispheres modulate immune response in an asymmetric manner have been confirmed in experiments on animals. Some authors assume that the right hemisphere plays an indirect role in neuroimmunomodulation, controlling and suppressing the left hemispheric inductive signals.

Mixed handedness is associated with greater age-related decline in volumes of the hippocampus and amygdala: the PATH through life study

Handedness has been found to be associated with structural and functional cerebral differences. Left handedness and mixed handedness also appear to be associated with an elevated risk of some developmental and immunological disorders that may contribute to pathological processes developing in ageing. Inconsistent reports show that left handedness may be more prevalent in early-onset as well as late-onset Alzheimer's disease, but might also be associated with slower decline. Such inconsistencies may be due to handedness being usually modeled as a binary construct while substantial evidence suggests it to be a continuous trait. The aim of this study was to investigate the relationship between brain structures known to be implicated in pathological ageing and strength and direction of handedness. The association between handedness and hippocampal and amygdalar atrophy was investigated in 327 cognitively healthy older individuals. Handedness was measured with the Edinburgh Inventory. Two measures were computed from this index, one reflecting the direction (left = 0/right = 1) and the other the degree of handedness (ranging from 0 to 1). Hippocampal and amygdalar volumes were manually traced on scans acquired 4 years apart. Regression analyses were used to assess the relationship between strength and direction of handedness and incident hippocampal and amygdalar atrophy. Analyses showed that strength but not direction of handedness was a significant predictor of hippocampal (Left: beta = 0.118, P = 0.013; Right: beta = 0.116, P = 0.010) and amygdalar (Right: beta = 0.105, P = 0.040) atrophy. The present findings suggest that mixed but not left handedness is associated with greater hippocampal and amygdalar atrophy. This effect may be due to genetic, environmental, or behavioural differences that will need further investigation in future studies.

A classification of handedness using the Annett Hand Preference Questionnaire

The Annett Hand Preference Questionnaire (AHPQ) was administered to a sample of 352 randomly selected individuals from the general community to examine the reproducibility of its handedness classification and to evaluate its model-based reliability and convergent validity. Latent class analysis showed that the eight categories of hand preferences could not be justified on statistical grounds. Instead, three broad handedness classes adequately accommodated the variety of handedness patterns: 'consistent right' (66.0%), 'consistent left' (9.8%) and 'inconsistent or mixed' (24.2%). Confirmatory factor analysis not only showed that the AHPQ is reliable and has solid convergent validity, but also the measurement properties of the AHPQ could be further improved by eliminating a few items from the scale. The implications of these findings are discussed, and it is suggested that questionnaire requires modification, possibly by replacing obsolete items such as 'sweeping' and 'shovelling' with modern manual activities, such as 'typing SMS messages' and 'using a remote control'.

Season of birth and risk for adult onset glioma

Adult onset glioma is a rare cancer which occurs more frequently in Caucasians than African Americans, and in men than women. The etiology of this disease is largely unknown. Exposure to ionizing radiation is the only well established environmental risk factor, and this factor explains only a small percentage of cases. Several recent studies have reported an association between season of birth and glioma risk. This paper reviews the plausibility of evidence focusing on the seasonal interrelation of farming, allergies, viruses, vitamin D, diet, birth weight, and handedness. To date, a convincing explanation for the occurrence of adult gliomas decades after a seasonal exposure at birth remains elusive.

Handedness, insulin sensitivity and pancreatic B-cell function in Type 2 diabetes

BACKGROUND

Laterality is associated with various health conditions. No study has addressed the influence of handedness on Type 2 diabetes mellitus (T2DM) phenotype, including glucose homeostasis, glucose-lowering therapies and metabolic control.

METHODS

Five hundred and seventy-six consecutive adult T2DM outpatients underwent homeostasis model assessment (HOMA) of pancreatic B-cell function (B), insulin sensitivity (S), hyperbolic product (B x S) and age-standardized B x S deficit. Right-handed patients (87.5%; RH; n = 504) had similar age, gender, diabetes duration and education than non-right-handed patients (12.5%; non-RH; n = 72).

RESULTS

Non-RH were more insulin-sensitive: 66% (39%) vs. 52% (36%) [mean (1 sd); P = 0.0024] and had significantly higher B x S and lower age-adjusted B x S deficit: 35% (20%) vs. 26% (17%) and 1.08% (0.40%) vs. 1.32% (0.55%)/year (non-RH; P = 0.0005 and P < 0.0001, respectively).

CONCLUSIONS

Non-right-handed T2DM patients are more insulin-sensitive, have higher hyperbolic product and less age-standardized B x S deficit. These may modulate glucose-lowering therapy requirements and glycaemic control.

Incidence of atypical handedness in epilepsy and its association with clinical factors

The incidence of atypical handedness (left-handedness and ambidexterity) in patients with epilepsy, particularly its association with major clinical factors, is not well established. We evaluated a full range of clinical variables in 478 patients with epilepsy from the United States and Korea. With the Edinburgh Handedness Inventory, handedness was established as both a categorical variable (right-handed, left-handed, ambidextrous) and a continuous variable. Seizures were classified as complex or simple partial, primary generalized, or generalized tonic-clonic. The relationship between handedness and a range of clinical findings was explored. The overall incidence of atypical handedness in our patients was higher than in the general population (13.6%) and significantly higher in the U.S. patient group (17.6%) than in the Korean patients (8.8%). Handedness was not associated with sex; age; seizure type; age at onset; type, side, or site of EEG or brain imaging abnormalities; family history of seizures; refractory epilepsy; or history of epilepsy surgery.

Effect of handedness on the Stroop Colour Word Task

Handedness is associated with cerebral organisation, but its relationship with cognition remains unclear. Since the Stroop task is believed to measure aspects of executive control, this study aims to investigate the effect of handedness on Stroop interference. We used the Stroop task with 90 young adults with university education, of whom 47 (23 males) were right-handed and 43 (21 males) were left-handed. Main dependent variables were Stroop baseline (SB), Stroop incongruent (SI), and the proportional derivative Stroop reduction (SR) [SR=(SB - SI)/SB×100%] (Bugg, Delosh, Davalos, & Davis, 2007; Graf, Uttl, &Tuokko, 1995) scores. The analysis revealed that SI is significantly affected by both handedness and the interaction of sex×handedness, whereas SR is only affected by handedness. After controlling for the effect of SB on SI, only the effect of handedness remained statistically significant [F(1, 83) = 6.44, p=.013]. Post-hoc comparisons showed that left-handed females performed significantly better than right-handed females on both SI (p=.003) and SR (p=.007). The data suggest that handedness is associated with cognitive function alterations, which lead to a smaller Stroop interference of left-handers irrespectively of sex, an effect that is more pronounced in the female subpopulation.

Comparative assessment of 13 of the widely used hand preference items in a Bulgarian sample

The hand preference items included into Chapman and Chapman's (1987) inventory were comparatively assessed concerning the frequencies of the answers given by Bulgarian right, mixed, and left handers, concerning the correlation of each item with the remaining 12, with eyedness and footedness scores. Relationships between writing hand, throwing hand, eyedness, and footedness were studied. Application of a cumulative index of familial sinistrality evidenced the biological significance of the main findings. All the results showed the inferiority of the writing hand as compared to the remaining items and evidenced the full inappropriateness of this item as a single predictor of handedness.

Nature's experiment? Handedness and early childhood development

In recent years, a large body of research has investigated the various factors affecting child development and the consequent impact of child development on future educational and labor market outcomes. In this article, we contribute to this literature by investigating the effect of handedness on child development. This is an important issue given that around 10% of the world's population is left-handed and given recent research demonstrating that child development strongly affects adult outcomes. Using a large, nationally representative sample of young children, we find that the probability of a child being left-handed is not significantly related to child health at birth, family composition, parental employment, or household income. We also find robust evidence that left-handed (and mixed-handed) children perform significantly worse in nearly all measures of development than right-handed children, with the relative disadvantage being larger for boys than girls. Importantly, these differentials cannot be explained by different socioeconomic characteristics of the household, parental attitudes, or investments in learning resources.

Manual asymmetry in a complex coincidence-anticipation task: handedness and gender effects

This study investigated the effects of handedness and gender on manual asymmetry in the performance of a complex coincidence-anticipation task. Left-handed (N=63) and right-handed (N=93) undergraduate students (78 males, 78 females) were required to press six buttons sequentially in conjunction with visual stimulation provided by a coincidence-anticipation apparatus. Participants were further separated into subgroups based on the degree of hand preference. Timing accuracy (AE, CE, VE) and timing response (IT, MT, AT) were analysed. Results showed that, concerning accuracy, (i) strong left-handers were more accurate than the other groups; (ii) performance with the preferred hand was superior to that of the non-preferred hand; and (iii) males outperformed females. Concerning timing response, (i) the preferred hand was faster than the non-preferred hand for movement time and (ii) males were faster in initiating the movement than females. These findings indicate that coincidence-anticipation competence appears to be influenced by hand preference, performing hand, and gender. In addition, findings are discussed in the framework of the hemispheric functional lateralisation for the planning and organisation of movement execution.

Zusammenhänge zwischen Händigkeit und motorischen und kognitiven Leistungen im Kindesalter

Zusammenfassung. In einer Längsschnittstudie wurden die Entwicklung der Händigkeit bei Kindergartenkindern (153 Jungen und 170 Mädchen) und deren Zusammenhänge mit motorischen und kognitiven Leistungen analysiert. Die Händigkeit wurde aufgrund der relativen Geschicklichkeit beider Hände bestimmt. Im Untersuchungszeitraum lässt sich keine Veränderung des Anteils von Rechtshändern (84.8%), Linkshändern (9.8%) und Ambidextern (5.4 %) nachweisen, Jungen sind häufiger linkshändig oder beidhändig als Mädchen. Der Anteil von Linkshändern bei Erstgeborenen, die ein höheres Risiko für Hirnschädigungen aufweisen, ist nicht höher als bei Nachgeborenen. Etwa 16 Prozent der Kinder, vor allem Linkshänder und Ambidexter, aber auch Rechtshänder, wechselten im Untersuchungszeitraum ihre Händigkeit. Linkshändigkeit oder Beidhändigkeit gehen nicht mit verminderten kognitiven oder motorischen Leistungen einher, allerdings erzielten Kinder, die im Untersuchungszeitraum ihre Händigkeit wechselten, schlechtere feinmotorische und kognitive Leistungen als Kinder mit konstanter Händigkeit.

Non-right-handedness is associated with migraine and soft bipolarity in patients with mood disorders

BACKGROUND

There is a substantial body of data showing differences in the functioning of the two hemispheres in unipolar depressive and bipolar disorders. Migraine is a frequent co-morbid disorder in these patients, and it has been proposed that migraine may be associated with left-handedness. It would therefore be interesting to study migraine and handedness in a population of patients with mood disorders.

METHODS

A total of 201 patients with an index episode of either major depression or mania were interviewed with a semi-structured interview based partly on DSM-IV criteria and partly on TEMPS-I for affective temperaments. The criteria of the Headache Classification Committee of the International Headache Society were used to establish the diagnosis of migraine. Hand preference was assessed using the Edinburgh inventory, and the patients were classified as having right-, left-, or mixed-handedness.

RESULTS

In the whole group 117 patients had migraine (58%) and 59 (29%) were classified as having non-right hand preference. There was a significant increased prevalence of non-right-handedness in the migraine group (37% vs. 19%, p=0.021, Chi-square test; OR 2.5; 95% CI 1.3 -4.8, p=0.007). In patients with cyclothymic, hyperthymic or irritable temperaments the prevalence of non-right-handedness (42%) was significantly higher (p=0.013, Chi-square test; OR 2.2, 95% CI 1.2-4.3) compared to patients with a depressive or no affective temperament (24%). The prevalence of non-right-handedness was also significantly higher both in patients with co-morbid eating disorders (48% vs. 26%, p=0.008 Chi-square test; OR 2.7, 95% CI 1.3-5.9, p=0.01) and asthma (45% vs. 26%, p=0.026 Chi-square test; OR 2.3, 95% CI 1.1-5.1, p=0.029).

LIMITATIONS

Non-blind evaluation of affective diagnosis, migraine and handedness.

CONCLUSIONS

Our main finding supports the hypothesis that non-right-handedness is associated with migraine and bipolar affective temperaments ("soft bipolarity") in a sample of patients with major affective disorders.

Is laterality associated with a higher rate of hip arthroplasty on the dominant side?

The authors analyzed data collected by the Registry of the Orthopedic Prosthetic Implantology in Italy. They found a higher rate of total hip arthroplasty on the right side (58%) in comparison with the left side in patients affected by primary coxarthrosis. To test whether laterality was the cause of this, they checked the prevalence of the upper and lower limbs in 262 patients treated for monolateral total hip prosthesis. They found that the percentage of left-handed patients was very low (0.8-6.5%). The percentage of left-footed patients was, instead, 26.5% for power tasks. They observed that, while the rate of arthroplasties on the right side was similar to that of the left side (50.7 and 49.3%) in the right-footed patients, there was a clear-cut prevalence in the number of operations on the right hip (76.8%) in comparison to the left one (23.2%) in the left-footed patients. The authors suggested that, in left-footed patients, the right side was subjected to greater stress.

Handedness and cognition across the healthy lifespan

The relationship between handedness and cognitive function varies across studies, perhaps partly due to the many medical and psychiatric conditions with known cognitive impact. This study examined cognitive performance in 643 healthy individuals (age 5-82) who were categorized as strongly right-handed, moderately right-handed, or left/mixed-handed. Cognitive differences emerged, as left/mixed-handed individuals demonstrating superior psychomotor speed and cognitive flexibility, and strongly and moderately right-handed individuals exhibiting better time estimation skills. No interaction-among handedness, sex, and age were found. These findings indicate cognitive differences associated with handedness exist independent of medical and psychiatric confounds. Further work is needed to clarify these findings.

Handedness and earnings

We examine whether handedness is related to performance in the labour market and, in particular, to earnings. We find a significant wage effect for left-handed men with high levels of education. This positive wage effect is strongest among those who have lower than average earnings relative to those of similar high education. This effect is not found among women.

The relationship between hand preference consistency, health, and accidents in a sample of adults over the age of 65 years

As a result of the Coren and Halpern (1991) hypothesis that left hand preference may be associated with decreased survival fitness, there has been interest in exploring the relationship between hand preference and indices of health status. In a series of studies of university-aged adults, Hicks and his colleagues found a higher prevalence of accidental injuries, falls, and sleep problems among individuals with mixed, rather than left, hand preference. They argued that hand preference consistency, not side, may be a marker for possible reduction in health and well-being. We looked at the relationship between hand preference consistency and the prevalence of sleep problems, accidental injuries, falls, injuries from falls, and the prevalence of autoimmune and other illnesses in a sample of 1277 adults between the ages of 65 and 100 years. Of those participants who reported a recent fall, mixed-handers were more likely to report a higher number of injuries from these falls when compared to the reports of consistent-handers. In contrast to the previous findings of Hicks et al., and highlighting the value of including broader age ranges, all other comparisons showed no differences between the two hand preference types.

Hand preference for writing and associations with selected demographic and behavioral variables in 255,100 subjects: the BBC internet study

In an Internet study unrelated to handedness, 134,317 female and 120,783 male participants answered a graded question as to which hand they preferred for writing. This allowed determination of hand preference patterns across 7 ethnic groups. Sex differences in left-handedness were found in 4 ethnic groups, favoring males, while no significant sex differences were found in three of the groups. Prevalence of left-handedness in the largest of the ethnic groups (self-labelled as "White") was comparable to contemporary hand preference data for this group [Gilbert, A. N., & Wysocki, C. J. (1992). Hand preference and age in the United states. Neuropsychologia, 30, 601-608] but the prevalence of left-handedness in individuals >70 years of age was considerably higher in the present study. Individuals who indicated "either" hand for writing preference had significantly lower spatial performance (mental rotation task) and significantly higher prevalence of hyperactivity, dyslexia, asthma than individuals who had clear left or right hand preferences, in support of Crow et al. [Crow, T., Crow, L., Done, D., & Leask, S. (1998). Relative hand skill predicts academic ability: global deficits at the point of hemispheric indecision. Neuropsychologia, 36, 1275-1282]. Similarly, an association of writing hand preference and non-heterosexual orientation was clearest for individuals with "either" writing hand responses. We conclude that contradictions in the literature as to whether or not these variables are linked to handedness stem largely from different definitions of hand preference. Due to a lack of statistical power in most studies in the literature, the "either" hand writing preference group that yielded the most salient results in this study is not normally available for analysis.