Evaluating the empirical support for the Geschwind-Behan-Galaburda model of cerebral lateralization

Joint exome and metabolome analysis in individuals with dyslexia: Evidence for associated dysregulations of olfactory perception and autoimmune functions

Dyslexia is a learning disability that negatively affects reading, writing, and spelling development at the word level in 5%-9% of children. The phenotype is variable and complex, involving several potential cognitive and physical concomitants such as sensory dysregulation and immunodeficiencies. The biological pathogenesis is not well-understood. Toward a better understanding of the biological drivers of dyslexia, we conducted the first joint exome and metabolome investigation in a pilot sample of 30 participants with dyslexia and 13 controls. In this analysis, eight metabolites of interest emerged (pyridoxine, kynurenic acid, citraconic acid, phosphocreatine, hippuric acid, xylitol, 2-deoxyuridine, and acetylcysteine). A metabolite-metabolite interaction analysis identified Krebs cycle intermediates that may be implicated in the development of dyslexia. Gene ontology analysis based on exome variants resulted in several pathways of interest, including the sensory perception of smell (olfactory) and immune system-related responses. In the joint exome and metabolite analysis, the olfactory transduction pathway emerged as the primary pathway of interest. Although the olfactory transduction and Krebs cycle pathways have not previously been described in dyslexia literature, these pathways have been implicated in other neurodevelopmental disorders including autism spectrum disorder and obsessive-compulsive disorder, suggesting the possibility of these pathways playing a role in dyslexia as well. Immune system response pathways, on the other hand, have been implicated in both dyslexia and other neurodevelopmental disorders.

Left-hand preference in visual artists: A pre-registered observational study on Instagram

The notion of an increased incidence of left handers among architects and visual artists has inspired both scientific theory building and popular discussion. However, a systematic exploration of the available publications provides, at best, modest evidence for this claim. The present preregistered observational study was designed to reinvestigate the postulated association by examining hand preference of visual artists who share their artistic activities as short video clips ("reels") on the social media platform Instagram. Determining individual hand preference based on five reels for each of N = 468 artists, we identified 42 (8.97%) left handers, suggesting an incidence which is below but statistical comparable to the 10.6% expected for the general population (χ2 = 1.30; p = .25; Cohen's w = 0.05). Also, we did not find any support for the notion that the art created by left-handed artists is of higher quality than art of right handers, as no difference in public endorsement or interest were observed (reflected by the number of likes per post or account followers). Taken together, we do not find any support for difference in artistic engagement or quality between left and right handers.

[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.

Assessing non-right-handedness and atypical cerebral lateralisation as predictors of paediatric mental health difficulties

Research utilising handedness as a proxy for atypical language lateralisation has invoked the latter to explain increased mental health difficulties in left-/mixed-handed children. The current study investigated unique associations between handedness and language lateralisation, handedness and mental health, and language lateralisation and mental health, in children, to elucidate the role of cerebral lateralisation in paediatric mental health. Participants were N = 64 (34 females [52%]; MAge  = 8.56 years; SDAge  = 1.33; aged 6-12 years) typically developing children. Hand preference was assessed via a reaching task, language lateralisation was assessed using functional transcranial Doppler ultrasonography (fTCD) during an expressive language task, and mental health was assessed with the Strengths and Difficulties Questionnaire. As hypothesised, leftward hand preference predicted increased general mental health issues in children, with a strong relationship noted between leftward hand preference and the emotional symptoms subscale. Contrary to expectation, no relationship was found between direction of language lateralisation and general mental health issues, although exploratory analyses of subscales showed rightward lateralisation to predict conduct problems. Hand preference and direction of language lateralisation were also not significantly associated. The relatively weak relationship between manual and language laterality coupled with discrepancy regarding the predictive scope of each phenotype (i.e., hand preference predicts overall mental health, whereas language laterality predicts only conduct problems) suggests independent developmental pathways for these phenotypes. The role of manual laterality in paediatric mental health warrants further investigation utilising a neuroimaging method with higher spatial resolution.

Elevated levels of mixed-hand preference in dyslexia: Meta-analyses of 68 studies

Since almost a hundred years, psychologists have investigated the link between hand preference and dyslexia. We present a meta-analysis to determine whether there is indeed an increase in atypical hand preference in dyslexia. We included studies used in two previous meta-analyses (Bishop, 1990; Eglinton & Annett, 1994) as well as studies identified through PubMed MEDLINE, PsycInfo, Google Scholar, and Web of Science up to August 2022. K = 68 studies (n = 4660 individuals with dyslexia; n = 40845 controls) were entered into three random effects meta-analyses using the odds ratio as the effect size (non-right-handers; left-handers; mixed-handers vs. total). Evidence of elevated levels of atypical hand preference in dyslexia emerged that were especially pronounced for mixed-hand preference (OR = 1.57), although this category was underdefined. Differences in (direction or degree) of hand skill or degree of hand preference could not be assessed as no pertinent studies were located. Our findings allow for robust conclusions only for a relationship of mixed-hand preference with dyslexia.

No Evidence of Creative Benefit Accompanying Dyslexia: A Meta-Analysis

Research on the question of creative benefit accompanying dyslexia has produced conflicting findings. In this meta-analysis, we determined summary effects of mean and variance differences in creativity between groups with and without dyslexia. Twenty studies were included (n = 770 individuals with dyslexia, n = 1,671 controls). A random-effects robust variance estimation (RVE) analysis indicated no mean (g = -0.02, p = .84) or variance (g = -0.0004, p = .99) differences in creativity between groups. The mean summary effect was moderated by age, gender, and creativity domain. Compared with adolescents, adults with dyslexia showed an advantage over nondyslexic adults in creativity. In addition, a higher proportion of males in the dyslexia group was associated with poorer performance compared with the controls. Finally, the dyslexia group showed a significant performance disadvantage in verbal versus figural creativity. Regarding variance differences, they varied across age and creativity domains. Compared with adults, adolescents showed smaller variability in the dyslexia group. If the creativity task measured verbal versus figural or combined creativity, the dyslexia group exhibited smaller variability. Altogether, our results suggest that individuals with dyslexia as a group are no more creative or show greater variability in creativity than peers without dyslexia.

Asymmetry in the Central Nervous System: A Clinical Neuroscience Perspective

Recent large-scale neuroimaging studies suggest that most parts of the human brain show structural differences between the left and the right hemisphere. Such structural hemispheric asymmetries have been reported for both cortical and subcortical structures. Interestingly, many neurodevelopmental and psychiatric disorders have been associated with altered functional hemispheric asymmetries. However, findings concerning the relation between structural hemispheric asymmetries and disorders have largely been inconsistent, both within specific disorders as well as between disorders. In the present review, we compare structural asymmetries from a clinical neuroscience perspective across different disorders. We focus especially on recent large-scale neuroimaging studies, to concentrate on replicable effects. With the notable exception of major depressive disorder, all reviewed disorders were associated with distinct patterns of alterations in structural hemispheric asymmetries. While autism spectrum disorder was associated with altered structural hemispheric asymmetries in a broader range of brain areas, most other disorders were linked to more specific alterations in brain areas related to cognitive functions that have been associated with the symptomology of these disorders. The implications of these findings are highlighted in the context of transdiagnostic approaches to psychopathology.

Dump the "dimorphism": Comprehensive synthesis of human brain studies reveals few male-female differences beyond size

With the explosion of neuroimaging, differences between male and female brains have been exhaustively analyzed. Here we synthesize three decades of human MRI and postmortem data, emphasizing meta-analyses and other large studies, which collectively reveal few reliable sex/gender differences and a history of unreplicated claims. Males' brains are larger than females' from birth, stabilizing around 11 % in adults. This size difference accounts for other reproducible findings: higher white/gray matter ratio, intra- versus interhemispheric connectivity, and regional cortical and subcortical volumes in males. But when structural and lateralization differences are present independent of size, sex/gender explains only about 1% of total variance. Connectome differences and multivariate sex/gender prediction are largely based on brain size, and perform poorly across diverse populations. Task-based fMRI has especially failed to find reproducible activation differences between men and women in verbal, spatial or emotion processing due to high rates of false discovery. Overall, male/female brain differences appear trivial and population-specific. The human brain is not "sexually dimorphic."

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.

An examination of the influence of prenatal sex hormones on handedness: Literature review and amniotic fluid data

Competing theories have posited roles for foetal androgen exposure in the development of human handedness. However, due to practical and ethical considerations, few studies have used hormonal measures to examine this possibility. The current paper reviews this literature and reveals a generally inconsistent pattern of results. We also present data from a longitudinal study of prenatal sex hormone exposure and subsequent handedness. More specifically, we examine correlations between testosterone and estradiol measured from second trimester amniotic fluid and hand preference (Dutch language version of the Edinburgh Handedness Inventory) and hand skill asymmetry (pegboard task) measured at 15 years of age. Prenatal sex hormone exposure was not associated with the direction of hand preference in either males or females. However, in females, high levels of prenatal testosterone were associated with weaker lateralisation of hand skill, and high levels of prenatal estradiol were associated with weaker hand preference. In addition, high levels of prenatal testosterone were associated with increased task duration (i.e., slow hand speed) for the right and left hands of males. The pattern of results observed here is not entirely consistent with any of the main theories linking sex hormones with handedness, suggesting that an association between these variables may be more complex than initially thought.

Digit ratio (2D:4D) and handedness: A meta-analysis of the available literature

The Geschwind-Behan-Galaburda and sexual differentiation models predict an association between elevated foetal androgen exposure and left-handedness whereas the callosal hypothesis predicts the opposite. We present a meta-analysis of correlations between handedness and digit ratio (2D:4D), a putative marker of prenatal testosterone. Left-handedness predicted low (male-typical) right-hand digit ratio (R2D:4D), high (female-typical) left-hand digit ratio (L2D:4D), and low R2D:4D-L2D:4D directional asymmetry (D_[R-L]). Effect sizes were extremely small and not moderated by sex or method of measuring handedness or 2D:4D. The same general pattern was observed after excluding the very large study (110,329 males, 90,412 females) of Manning and Peters ([2009]. Digit ratio (2D:4D) and hand preference for writing in the BBC Internet Study. Laterality: Asymmetries of Body, Brain and Cognition, 14(5), 528-540. doi:10.1080/13576500802637872); however, no significant effects for R2D:4D were observed once these samples were removed. The results do not confirm any theory linking prenatal androgens with handedness, so we speculate they instead reflect the mechanical action of writing causing subtle changes in the musculature and/or fat pads of the fingers. Gripping a pen/pencil might cause an increase in 2D relative to 4D (and/or decrease in 4D relative to 2D) resulting in higher ratios on the writing-hand; furthermore, this could differ between left- and right-handers due to writing in the left-to-right direction (as in English) having asymmetrical effects depending on which hand is used.

Clinical correlates of laterality among school-age children in the United States

Researchers have long been interested in whether lateral preference is associated with giftedness, season of birth, and/or ADHD constructs (short attention span, high level of activity, and impulsivity). The objective of this study was to examine these associations in a large, longitudinal sample of U.S. children (National Collaborative Perinatal Project (CPP), 1959-1973). Children born to women in this pregnancy cohort underwent a neonatal exam and an exam at age 7 years to assess lateral preference of the hand and eye, IQ on the Wechsler Intelligence Scale for Children (WISC), and ADHD symptoms. Children with perinatal/neonatal risk factors for neurologic impairment or early signs of neurological abnormality were excluded from our analyses. The final sample included 25,385 children. Associations between laterality and IQ were examined using linear and logistic regression models adjusted for sex, race, and socioeconomic status. Associations between laterality and ADHD symptoms and between season of birth and laterality were estimated using multivariable logistic regression. In this large, longitudinal study of neurologically healthy children, modest associations were observed between hand/eye preference and IQ and hyperactivity only.

Testosterone effects on functional amygdala lateralization: A study in adolescent transgender boys and cisgender boys and girls

The influence of testosterone on the development of human brain lateralization has been subject of debate for a long time, partly because studies investigating this are necessarily mostly correlational. In the present study we used a quasi-experimental approach by assessing functional brain lateralization in trans boys (female sex assigned at birth, diagnosed with Gender Dysphoria, n = 21) before and after testosterone treatment, and compared these results to the functional lateralization of age-matched control groups of cisgender boys (n = 20) and girls (n = 21) around 16 years of age. The lateralization index of the amygdala was determined with functional magnetic resonance imaging (fMRI) during an emotional face matching task with angry and fearful faces, as the literature indicates that boys show more activation in the right amygdala than girls during the perception of emotional faces. As expected, the lateralization index in trans boys shifted towards the right amygdala after testosterone treatment, and the cumulative dose of testosterone treatment correlated significantly with amygdala lateralization after treatment. However, we did not find any significant group differences in lateralization and endogenous testosterone concentrations predicted rightward amygdala lateralization only in the cis boys, but not in cis girls or trans boys. These inconsistencies may be due to sex differences in sensitivity to testosterone or its metabolites, which would be a worthwhile course for future studies.

Genetic effects on planum temporale asymmetry and their limited relevance to neurodevelopmental disorders, intelligence or educational attainment

Previous studies have suggested that altered asymmetry of the planum temporale (PT) is associated with neurodevelopmental disorders, including dyslexia, schizophrenia, and autism. Shared genetic factors have been suggested to link PT asymmetry to these disorders. In a dataset of unrelated subjects from the general population (UK Biobank, N = 18,057), we found that PT volume asymmetry had a significant heritability of roughly 14%. In genome-wide association analysis, two loci were significantly associated with PT asymmetry, including a coding polymorphism within the gene ITIH5 that is predicted to affect the protein's function and to be deleterious (rs41298373, p = 2.01 × 10-15), and a locus that affects the expression of the genes BOK and DTYMK (rs7420166, p = 7.54 × 10-10). DTYMK showed left-right asymmetry of mRNA expression in post mortem PT tissue. Cortex-wide mapping of these SNP effects revealed influences on asymmetry that went somewhat beyond the PT. Using publicly available genome-wide association statistics from large-scale studies, we saw no significant genetic correlations of PT asymmetry with autism spectrum disorder, attention deficit hyperactivity disorder, schizophrenia, educational attainment or intelligence. Of the top two individual loci associated with PT asymmetry, rs41298373 showed a tentative association with intelligence (unadjusted p = .025), while the locus at BOK/DTYMK showed tentative association with educational attainment (unadjusted Ps < .05). These findings provide novel insights into the genetic contributions to human brain asymmetry, but do not support a substantial polygenic association of PT asymmetry with cognitive variation and mental disorders, as far as can be discerned with current sample sizes.

Cerebral laterality as assessed by hand preference measures and developmental stuttering

The causes of developmental stuttering, a neurodevelopmental communicative disorder, have not been elucidated to date. Neuroimaging studies suggest that atypical cerebral laterality could be one of such causal factors. Moreover, handedness, a behavioural index for cerebral laterality, has been linked to stuttering and recovery from it. However, findings are conflicting, possibly due to sample selection procedures, which typically rely on self-reported stuttering, and to the fact that handedness is typically assessed with regards to its direction rather than degree. We investigated the possible relationship between handedness and stuttering. This is the first study where children who stutter (CWS) were selected using clinical criteria as well as speech samples and where a non-Western population was studied. Findings from 83 CWS aged 3-9 years (mean = 6.43, SD = 1.84) and 90 age- and sex-matched children who do not stutter (mean = 6.45, SD = 1.71) revealed no differences in their hand preference scores as evaluated by parent-completed Edinburgh Handedness Inventory, for both direction and degree. The severity of stuttering was not found to correlate with the degree of handedness. We suggest that parents and professionals not treat left- or mixed-hand preference as a reason for concern with regards to stuttering.

Half a century of handedness research: Myths, truths; fictions, facts; backwards, but mostly forwards

Although most people are right-handed and have language in their left cerebral hemisphere, why that is so, and in particular why about ten per cent of people are left-handed, is far from clear. Multiple theories have been proposed, often with little in the way of empirical support, and sometimes indeed with strong evidence against them, and yet despite that have become modern urban myths, probably due to the symbolic power of right and left. One thinks in particular of ideas of being right-brained or left-brained, of suggestions that left-handedness is due to perinatal brain damage, of claims that left-handers die seven years earlier than right-handers, and of the unfalsifiable ramifications of the byzantine Geschwind-Behan-Galaburda theory. This article looks back over the past fifty years of research on brain asymmetries, exploring the different themes and approaches, sometimes in relation to the author's own work. Taking all of the work together it is probable that cerebral asymmetries are under genetic control, probably with multiple genetic loci, only a few of which are now beginning to be found thanks to very large databases that are becoming available. Other progress is also seen in proper meta-analyses, the use of fMRI for studying multiple functional lateralisations in large number of individuals, fetal ultra-sound for assessing handedness before birth, and fascinating studies of lateralisation in an ever widening range of animal species. With luck the next fifty years will make more progress and show fewer false directions than had much of the work in the previous fifty years.

Meta-analytic findings reveal lower means but higher variances in visuospatial ability in dyslexia

Conflicting empirical and theoretical accounts suggest that dyslexia is associated with either average, enhanced, or impoverished high-level visuospatial processing relative to controls. Such heterogeneous results could be due to the presence of wider variability in dyslexic samples, which is unlikely to be identified at the single study level, due to lack of power. To address this, this study reports a meta-analysis of means and variances in high-level visuospatial ability in 909 non-dyslexic and 956 dyslexic individuals. The findings suggest that dyslexia is associated not only with a lower mean performance on visuospatial tasks but also with greater variability in performance. Through novel meta-analytic techniques, we demonstrate a negative effect size for mean differences (-.457), but a positive effect size for SD differences (+.118; SD ratio = 1.107). In doing so, this is the first study to demonstrate impoverished visuospatial processing of the majority of individuals with dyslexia in addition to greater variance in performance in this group. The findings advocate for further consideration of both the presence of, and reasons for, increased variance in perception, attention, and memory across neurodevelopmental disorders.

Sex/gender differences in cognition, neurophysiology, and neuroanatomy

In this mini-review, I summarize and interpret the current status of sex/gender differences in terms of brain anatomy, brain function, behavior, and cognition. Based on this review and the reported findings, I conclude that most of these sex/gender differences are not large enough to support the assumption of sexual dimorphism in terms of brain anatomy, brain function, cognition, and behavior. Instead, I suggest that many brain and cognitive features are modulated by environment, culture, and practice (and several other influences). These influences interact with the menstrual cycle, the general hormone level, and current gender stereotypes in a way that has not yet been fully understood.

Differential responses of stressful elements to predatory exposure in behavior-lateralized mice

BACKGROUND

Predatory stress as a psychological stressor can elicit the activation of the hypothalamic-pituitary-adrenal (HPA) axis, which is involved in the dialogue of the neuroimmunoendocrine network. The brain has been proven to regulate the activity of the HPA axis by way of lateralization. In the present study, we probed the pivotal elements of the HPA circuitry including CRH, GR and a multifunctional cytokine in behavior-lateralized mice to determine their changes when the animals were subjected to predator exposure.

METHODS

Behavior-lateralized mice were classified into left-pawed and right-pawed mice through a paw-preference test. Thereafter, mice in the acute stress group received a single 60-min cat exposure, and mice in the chronic group received daily 60-min cat exposure for 14 consecutive days. The plasma CS and TNF-α were determined by ELISA, the hypothalamic CRH mRNA and hippocampal GR mRNA were detected by real-time PCR, and the hippocampal GR protein was detected by western blot analysis.

RESULTS

The results revealed that the levels of plasma CS were significantly elevated after chronic predatory exposure in both right-pawed and left-pawed mice; the right-pawed mice exhibited a higher plasma CS level than the left-pawed mice. Similarly, the acute or chronic cat exposure could induce the release of plasma TNF-α, and the left-pawed mice tended to show a higher level after the acute stress. Chronic stress significantly upregulated the expression of hypothalamic CRH mRNA in both left-pawed and right-pawed mice. Normally, the left-pawed mice exhibited a higher GR expression in the hippocampus than the right-pawed mice. After the cat exposure, the expression of GR in both left-pawed and right-pawed mice was revealed to be greatly downregulated.

CONCLUSION

Our findings indicate that predatory stress can invoke a differential response of stressful elements in behavior-lateralized mice. Some of these responses shaped by behavioral lateralization might be helpful for facilitating adaption to various stimuli.

Triplets, birthweight, and handedness

The mechanisms behind handedness formation in humans are still poorly understood. Very low birthweight is associated with higher odds of left-handedness, but whether this is due to low birthweight itself or premature birth is unknown. Handedness has also been linked to development, but the role of birthweight behind this association is unclear. Knowing that birthweight is lower in multiple births, triplets being about 1.5 kg lighter in comparison with singletons, and that multiples have a higher prevalence of left-handedness than singletons, we studied the association between birthweight and handedness in two large samples consisting exclusively of triplets from Japan (n = 1,305) and the Netherlands (n = 947). In both samples, left-handers had significantly lower birthweight (Japanese mean = 1,599 g [95% confidence interval (CI): 1,526-1,672 g]; Dutch mean = 1,794 g [95% CI: 1,709-1,879 g]) compared with right-handers (Japanese mean = 1,727 g [95% CI: 1,699-1,755 g]; Dutch mean = 1,903 g [95% CI: 1,867-1,938 g]). Within-family and between-family analyses both suggested that left-handedness is associated with lower birthweight, also when fully controlling for gestational age. Left-handers also had significantly delayed motor development and smaller infant head circumference compared with right-handers, but these associations diluted and became nonsignificant when controlling for birthweight. Our study in triplets provides evidence for the link between low birthweight and left-handedness. Our results also suggest that developmental differences between left- and right-handers are due to a shared etiology associated with low birthweight.

Allergic tendencies are associated with larger gray matter volumes

Allergic tendencies are associated with important cognitive and physiological factors, such as intelligence and mathematical abilities. Allergies are widely prevalent, especially in modern life, and the reason for its association with important cognitive variables is an intriguing scientific question. However, despite the unique characteristics of cognitive correlates of allergy, the anatomical correlates of allergy remain unknown. The aim of this study was to identify the associations between regional gray matter volume (rGMV) and allergic tendencies in young adults. In a study cohort of 1,219 healthy, educated young adults, we identified a positive correlation between total allergic tendency and rGMV in large anatomical clusters that mainly encompassed the dorsal part of the cerebral neocortex, right anterior insula, and cerebellum. Furthermore,both mean rGMV of the entire part of these clusters and total allergenic tendency showed a significant positive correlation with spatial ability. These results suggest the link among allergic tendencies, larger rGMV, and the better spatial ability in healthy, educated young adults.

The SETDB2 locus: evidence for a genetic link between handedness and atopic disease

The gene SETDB2, which mediates aspects of laterality in animal model systems, has recently been linked with human handedness as measured continuously on a scale from strong left to strong right. By contrast, it was marginally associated with a left-right dichotomous measure, and it showed no evidence of association with absolute handedness strength independent of direction. We genotyped the SETDB2 handedness-associated single nucleotide polymorphism, rs4942830, in a large healthy population likewise phenotyped for continuous, absolute, and dichotomous handedness variables. Our results demonstrated significant effects of rs4942830 genotype on continuous handedness, and weaker, marginal effects on dichotomous handedness, but no effects on absolute handedness. These results help to establish the locus marked by the SNP rs4942830 as a strong candidate for mediating human handedness. Intriguingly, rs4942830 is also in complete linkage disequilibrium with rs386770867, a polymorphism recently shown to affect human serum levels of IgE production and other atopic phenotypes. These findings implicate this locus in the longstanding links of handedness with asthma and other atopic diseases.

Associations of parental age with health and social factors in adult offspring. Methodological pitfalls and possibilities

Parental age is increasing rapidly in many countries. Analysis of this potentially important influence on offspring well-being is hampered by strong secular trends and socioeconomic patterning and by a shortage of follow-up data for adult offspring. We used Swedish national data on up to 3,653,938 offspring to consider the associations of parental age with a suite of outcomes in adult offspring, comparing the results from an array of statistical methods for optimal causal inference. The offspring of older mothers had higher BMI, blood pressure, height, intelligence, non-cognitive ability and socioeconomic position. They were less likely to smoke or to be left-handed. Associations with paternal age were strongly, but not completely, attenuated by adjustment for maternal age. Estimates from the commonly-used sibling comparison method were driven primarily by a pathway mediated by offspring date of birth when outcomes showed strong secular trends. These results suggest that the intra-uterine and early life environments provided by older mothers may be detrimental to offspring cardiovascular health, but that their greater life experience and social position may bring intellectual and social advantages to their offspring. The analysis of parental age presents particular challenges, and further methodological developments are needed.

Cerebral laterality for language is related to adult salivary testosterone levels but not digit ratio (2D:4D) in men: A functional transcranial Doppler ultrasound study

The adequacy of three competing theories of hormonal effects on cerebral laterality are compared using functional transcranial Doppler sonography (fTCD). Thirty-three adult males participated in the study (21 left-handers). Cerebral lateralization was measured by fTCD using an extensively validated word generation task. Adult salivary testosterone (T) and cortisol (C) concentrations were measured by luminescence immunoassay and prenatal T exposure was indirectly estimated by the somatic marker of 2nd to 4th digit length ratio (2D:4D). A significant quadratic relationship between degree of cerebral laterality for language and adult T concentrations was observed, with enhanced T levels for strong left hemisphere dominance and strong right hemisphere dominance. No systematic effects on laterality were found for cortisol or 2D:4D. Findings suggest that higher levels of T are associated with a relatively attenuated degree of interhemispheric sharing of linguistic information, providing support for the callosal and the sexual differentiation hypotheses rather than the Geschwind, Behan and Galaburda (GBG) hypothesis.

Are hormone levels and cognitive ability related during early adolescence?

The present study assessed the longstanding question of whether there is a relationship between sex hormones and cognitive ability in young adolescent girls and boys. Three “theories” of the relationship between hormone levels and cognition were identi” ed from a broad literature base and were used to formulate hypotheses regarding the relationship between sex hormones and cognitive ability in early adolescents. Fifty-six boys, aged 10-14, and 52 girls, aged 9-14, completed two standardised spatial ability tests and one standardised test of verbal ability. Three blood samples, at 20-minute intervals, were obtained to determine levels of estradiol and testosterone. Data were collected on three occasions for all measures at 6-month intervals. A positive linear relationship between testosterone and spatial ability was identi” ed for boys at each time of measurement for both measures of spatial ability (i.e., mental rotation and block design). For girls, a positive linear relationship was identi” ed between testosterone and mental rotation only at time 3. In addition, longitudinal relationships were identi” ed between change in testosterone levels and change in spatial ability for both girls and boys. The conclusion was that testosterone is related to cognitive functioning during pubertal development for boys and to a lesser extent for girls.

Memories of Phil Bryden

Phil Bryden was a seminal figure in the development of the field of cerebral lateralization in the last half of the twentieth century, and a founding editor of this journal. Here his founding co-editors reminisce about their friend and colleague, and reflect on his wide-ranging influence in the field and in their own careers.

Prenatal testosterone and stuttering

BACKGROUND

The prevalence of stuttering is much higher in males compared to females. The biological underpinnings of this skewed sex-ratio is poorly understood, but it has often been speculated that sex hormones could play an important role.

AIMS

The present study investigated a potential link between prenatal testosterone and stuttering. Here, an indirect indicator of prenatal testosterone levels, the Digit Ratio (2D:4D) of the hand, was used. As numerous studies have shown, hands with more "male" characteristics (putatively representing greater prenatal testosterone levels) are characterized by a longer ring finger compared to the index finger (represented as a lower 2D:4D ratio) in the general population.

STUDY DESIGN, SUBJECTS, OUTCOME MEASURES

We searched for differences in the 2D:4D ratios between 38 persons who stutter and 36 persons who do not stutter. In a second step, we investigated potential links between the 2D:4D ratio and the multifaceted symptomatology of stuttering, as measured by the Overall Assessment of the Speaker's Experience of Stuttering (OASES), in a larger sample of 44 adults who stutter.

RESULTS

In the first step, no significant differences in the 2D:4D were observed between individuals who stutter and individuals who do not stutter. In the second step, 2D:4D correlated negatively with higher scores of the OASES (representing higher negative experiences due to stuttering), and this effect was more pronounced for female persons who stutter.

CONCLUSIONS

The findings indicate for the first time that prenatal testosterone may influence individual differences in psychosocial impact of this speech disorder.

Quantifying cerebral asymmetries for language in dextrals and adextrals with random-effects meta analysis

Speech and language-related functions tend to depend on the left hemisphere more than the right in most right-handed (dextral) participants. This relationship is less clear in non-right handed (adextral) people, resulting in surprisingly polarized opinion on whether or not they are as lateralized as right handers. The present analysis investigates this issue by largely ignoring methodological differences between the different neuroscientific approaches to language lateralization, as well as discrepancies in how dextral and adextral participants were recruited or defined. Here we evaluate the tendency for dextrals to be more left hemisphere dominant than adextrals, using random effects meta analyses. In spite of several limitations, including sample size (in the adextrals in particular), missing details on proportions of groups who show directional effects in many experiments, and so on, the different paradigms all point to proportionally increased left hemispheric dominance in the dextrals. These results are analyzed in light of the theoretical importance of these subtle differences for understanding the cognitive neuroscience of language, as well as the unusual asymmetry in most adextrals.

The higher prevalence of non-right handers among patients with restless leg syndrome

Restless leg syndrome (RLS) is a common disorder described as an urge to move the legs. Dopamine, the main neuro-transmitter in the pathophysiology of RLS, is likely related to the development of brain laterality and human handedness. We aimed to compare the prevalence of RLS in right and non-right handers. A checklist including Edinburgh questioner for handedness, questions for RLS diagnosis and basic characteristics was filled out by a sample of population. The exclusion criteria included prolonged use of dopaminergic or psychologic drugs and having diseases with similar symptoms to RLS. The frequency of non-right handers in RLS patients was compared with the controls by Chi square test. P value less than 0.05 was considered significant. 164 persons were divided into RLS patients (69) and non-RLS controls (95). There was no significant difference between demographic characteristics. The prevalence of non-right handers in RLS patients was significantly more than non-RLS controls (P: 0.03). Our finding regarding the higher prevalence of non-right handers in RLS patients needs more justifications based on neuroscientists' guides. RLS as a disease in which dopaminergic system involves is highly assumed to be linked with handedness. This is just a hypothesis that impaired modulation of immune system in left handers may be accompanied with lower dopamine levels in RLS.

Negative affectivity and EEG asymmetry interact to predict emotional interference on attention in early school-aged children

Negative affectivity (NA) is a broad construct that has been associated with the development of psychopathologies, such as anxiety, and with exaggerated attention to threatening stimuli. EEG asymmetry reflects biological individual differences in emotional reactivity that may underlie the association between NA and attention to threat. The present study included a sample of 31 five-seven year olds (M age in months=74.39, SD=6.57) to test the hypothesis that greater NA, combined with greater right anterior and posterior asymmetries, predicts increased attention interference following threat stimuli. Children completed an executive attention task which presented task-irrelevant threat (angry) and non-threat (neutral) faces prior to each trial. EEG asymmetry was measured at baseline for anterior, anterior-temporal and posterior scalp regions and child NA was measured via maternal report. As predicted, children showing greater NA and greater right anterior-temporal asymmetry showed more attention interference following angry faces. Additionally, two trend-level effects emerged: children showing greater NA and greater left anterior-temporal asymmetry showed less attention interference following angry faces, and children showing greater NA and greater left posterior asymmetry showed less attention interference, but only following neutral faces. Discussion focuses on the utility of using EEG asymmetry in the study of temperament, attentional biases, and the biological processes by which temperament confers risk for psychopathology.

An fMRI study of nonverbally gifted reading disabled adults: has deficit compensation effected gifted potential?

Neuroscience has advanced our understanding of the neurological basis of reading disability (RD). Yet, no functional imaging work has been reported on the twice-exceptional dyslexic: individuals exhibiting both non-verbal-giftedness and RD. We compared groups of reading-disabled (RD), non-verbally-gifted (G), non-verbally-gifted-RD (GRD), and control (C) adults on validated word-rhyming and spatial visualization fMRI tasks, and standardized psychometric tests, to ascertain if the neurological functioning of GRD subjects was similar to that of typical RD or G subjects, or perhaps some unique RD subtype. Results demonstrate that GRD adults resemble non-gifted RD adults in performance on paper-and-pencil reading, math and spatial tests, and in patterns of functional activation during rhyming and spatial processing. Data are consistent with what may be a shared etiology of RD and giftedness in GRD individuals that yields a lifespan interaction with reading compensation effects, modifying how their adult brain processes text and spatial stimuli.

Familial sinistrals avoid exact numbers

We report data from an internet questionnaire of sixty number trivia. Participants were asked for the number of cups in their house, the number of cities they know and 58 other quantities. We compare the answers of familial sinistrals – individuals who are left-handed themselves or have a left-handed close blood-relative – with those of pure familial dextrals – right-handed individuals who reported only having right-handed close blood-relatives. We show that familial sinistrals use rounder numbers than pure familial dextrals in the survey responses. Round numbers in the decimal system are those that are multiples of powers of 10 or of half or a quarter of a power of 10. Roundness is a gradient concept, e.g. 100 is rounder than 50 or 200. We show that very round number like 100 and 1000 are used with 25% greater likelihood by familial sinistrals than by pure familial dextrals, while pure familial dextrals are more likely to use less round numbers such as 25, 60, and 200. We then use Sigurd’s (1988, Language in Society) index of the roundness of a number and report that familial sinistrals’ responses are significantly rounder on average than those of pure familial dextrals. To explain the difference, we propose that the cognitive effort of using exact numbers is greater for the familial sinistral group because their language and number systems tend to be more distributed over both hemispheres of the brain. Our data support the view that exact and approximate quantities are processed by two separate cognitive systems. Specifically, our behavioral data corroborates the view that the evolutionarily older, approximate number system is present in both hemispheres of the brain, while the exact number system tends to be localized in only one hemisphere.

Behavioral genetic variation, adaptation and maladaptation: an evolutionary perspective

Evolutionary psychology seeks to understand the adaptive, evolved nature of humans by considering the forces of natural selection that gave rise to it. Individual humans also exhibit maladaptation, however, and some of the variation in maladaptive conditions is heritable. An evolutionary perspective can shed light on these phenomena too. Recent work suggests that developmental imprecision importantly affects the fitness of organisms and some of the genetic influences have been identified. Both theory and evidence that developmental imprecision underlies human cognitive maladaptation has begun to accumulate, although the manner in which the developing brain is affected remains largely unknown.

Handedness is modulated by sex and self-perception

The distribution of handedness is different for men and women. Less pronounced right- or left-handedness in men is well established and often attributed to direct effects of genetic factors. Many studies observing this sex difference assessed handedness via questionnaire. It may therefore be influenced by a sex-specific bias in self-perception. Permanent inadequate self-perceptions are key characteristics of hypochondriasis. The study therefore tested 1017 participants (614 females) on two standard questionnaires to assess handedness and hypochondriasis: the Edinburgh Inventory and the Whiteley Index. Effects of sex, hypochondriac traits and the direction of handedness (left-handers; right-handers) on the degree of handedness (DH; the strength of lateralisation) were tested with multivariate linear regression. In confirmation of previous results, the DH is lower (less pronounced) in right-handed males than right-handed females, but is similar across sexes in left-handers. Regression analyses showed that for right-handers, male sex and higher hypochondriac traits are independent predictors of lower DH. For left-handers, main effects of sex and hypochondriac traits are not significant whereas a significant interaction of these two factors indicates that in left-handed men higher hypochondriac traits are associated with a differentially stronger shift towards lower DH compared to left-handed women. In conclusion, the DH is modulated by sex-specific effects of self-perception for left-handers but not right-handers. The implications of this finding on current theories of the inheritance of handedness are discussed. The assessment of hypochondriac traits might be useful to control response bias in questionnaire-based studies of human handedness.

Hand preference in humans is associated with testosterone levels and androgen receptor gene polymorphism

Exposure of the central nervous system to androgens during the early developmental period has been proposed to play a role in the establishment of hand preference in males. Existing data, however, are inconclusive. In the present investigation, handedness was assessed in a large sample of left-, mixed-, and right-handed men (N=180) using a standardized handedness inventory. Saliva sampling was used to assay levels of bioavailable testosterone and DNA genotyping was carried out to quantify AR-CAG repeat length, a genetic marker of the capacity of the androgen receptor to respond to testosterone. Strongly left-handed males were found to have lower levels of bioavailable testosterone than right-handed males, while males with mixed handedness exhibited a weaker androgen receptor, but no significant difference from right-handers in circulating testosterone levels. These findings support the view that testosterone could play a role in the development of hand preference in males. Furthermore, because the AR gene lies on the X chromosome, it provides a potential theoretical bridge to genetic theories of handedness that postulate the existence of an X-linked locus important in the establishment of hand preference.