Hand preference and hand skill in families with schizophrenia

Exploring cerebral laterality of writing and the relationship to handedness: a functional transcranial Doppler ultrasound investigation

Cerebral lateralization of oral language has been investigated in a plethora of studies and it is well established that the left hemisphere is dominant for production tasks in the majority of individuals. However, few studies have focused on written language and even fewer have sampled left-handers. Writing comprises language and motor components, both of which contribute to cerebral activation, yet previous research has not disentangled. The aim of this study was to disentangle the language and motor components of writing lateralization. This was achieved through the comparison of cerebral activation during (i) written word generation and (ii) letter copying, as assessed by functional Transcranial Doppler (fTCD) ultrasound. We further assessed cerebral laterality of oral language. The sample was balanced for handedness. We preregistered the hypotheses that (i) cerebral lateralization of the linguistic component of writing would be weaker in left-handers compared to right-handers and (ii) oral language and the linguistic component of written language would not be correlated in terms of cerebral lateralization. No compelling evidence for either of our hypotheses was found. Findings highlight the complexity of the processes subserving written and oral language as well as the methodological challenges to isolate the linguistic component of writing.

Large-scale analysis of structural brain asymmetries in schizophrenia via the ENIGMA consortium

Left-right asymmetry is an important organizing feature of the healthy brain that may be altered in schizophrenia, but most studies have used relatively small samples and heterogeneous approaches, resulting in equivocal findings. We carried out the largest case-control study of structural brain asymmetries in schizophrenia, with MRI data from 5,080 affected individuals and 6,015 controls across 46 datasets, using a single image analysis protocol. Asymmetry indexes were calculated for global and regional cortical thickness, surface area, and subcortical volume measures. Differences of asymmetry were calculated between affected individuals and controls per dataset, and effect sizes were meta-analyzed across datasets. Small average case-control differences were observed for thickness asymmetries of the rostral anterior cingulate and the middle temporal gyrus, both driven by thinner left-hemispheric cortices in schizophrenia. Analyses of these asymmetries with respect to the use of antipsychotic medication and other clinical variables did not show any significant associations. Assessment of age- and sex-specific effects revealed a stronger average leftward asymmetry of pallidum volume between older cases and controls. Case-control differences in a multivariate context were assessed in a subset of the data (N = 2,029), which revealed that 7% of the variance across all structural asymmetries was explained by case-control status. Subtle case-control differences of brain macrostructural asymmetry may reflect differences at the molecular, cytoarchitectonic, or circuit levels that have functional relevance for the disorder. Reduced left middle temporal cortical thickness is consistent with altered left-hemisphere language network organization in schizophrenia.

Evolution of cerebral asymmetry

The human brain is often characterized in terms of a duality, with the left and right brains serving complementary functions, and even individuals are sometimes classified as either "left-brained" or "right-brained." Recent evidence from brain imaging shows that hemispheric asymmetry is multidimensional, comprised of independent lateralized circuits. Cerebral asymmetries, which include handedness, probably arise in phylogenesis through the fissioning of ancestral systems that divided and lateralized with increasing demand for specialization. They also vary between individuals, with some showing absent or reversed asymmetries. It is unlikely that this variation is controlled by a single gene, as sometimes assumed, but depends rather on complex interplay among several, perhaps many, genes. Hemispheric asymmetry has often been regarded as a unique mark of being human, but it has also become evident that behavioral and cerebral asymmetries are not confined to humans, and are widespread among animal species. They nevertheless exist against a fundamental background of bilateral symmetry, suggesting a tradeoff between the two. Individual differences in asymmetry, moreover, are themselves adaptive, contributing to the cognitive and behavioral specializations necessary for societies to operate efficiently.

Human subcortical brain asymmetries in 15,847 people worldwide reveal effects of age and sex

The two hemispheres of the human brain differ functionally and structurally. Despite over a century of research, the extent to which brain asymmetry is influenced by sex, handedness, age, and genetic factors is still controversial. Here we present the largest ever analysis of subcortical brain asymmetries, in a harmonized multi-site study using meta-analysis methods. Volumetric asymmetry of seven subcortical structures was assessed in 15,847 MRI scans from 52 datasets worldwide. There were sex differences in the asymmetry of the globus pallidus and putamen. Heritability estimates, derived from 1170 subjects belonging to 71 extended pedigrees, revealed that additive genetic factors influenced the asymmetry of these two structures and that of the hippocampus and thalamus. Handedness had no detectable effect on subcortical asymmetries, even in this unprecedented sample size, but the asymmetry of the putamen varied with age. Genetic drivers of asymmetry in the hippocampus, thalamus and basal ganglia may affect variability in human cognition, including susceptibility to psychiatric disorders.

The Many Sides of Hemispheric Asymmetry: A Selective Review and Outlook

Hemispheric asymmetry is commonly viewed as a dual system, unique to humans, with the two sides of the human brain in complementary roles. To the contrary, modern research shows that cerebral and behavioral asymmetries are widespread in the animal kingdom, and that the concept of duality is an oversimplification. The brain has many networks serving different functions; these are differentially lateralized, and involve many genes. Unlike the asymmetries of the internal organs, brain asymmetry is variable, with a significant minority of the population showing reversed asymmetries or the absence of asymmetry. This variability may underlie the divisions of labor and the specializations that sustain social life. (JINS, 2017, 23, 710-718).

The imprinted gene LRRTM1 mediates schizotypy and handedness in a nonclinical population

Imprinted genes have been posited to have important roles in human brain development and cognition, but their effects in nonclinical populations have yet to be investigated. Single-nucleotide polymorphisms (SNPs) of the imprinted gene LRRTM1 have previously been associated with schizophrenia risk and with handedness in individuals with dyslexia. We tested the hypothesis that genetic variation (SNPs) and epigenetic variation (methylation) in this gene are associated with schizotypy and handedness in a nonclinical population. Risk alleles of the three schizophrenia-linked SNPs were associated with significantly and substantially higher levels of total schizotypy. Variation in SNP genotypes was not associated with handedness, but levels of methylation in a block of CpG sites in the putative LRRTM1 promoter region were associated with more-mixed handedness. These findings provide evidence of continuity between schizophrenia and schizotypy with regard to the psychological effects of allelic variation in this imprinted gene, and show that epigenetic variation in an imprinted gene mediates the development and expression of human handedness.

Left brain, right brain: facts and fantasies

Handedness and brain asymmetry are widely regarded as unique to humans, and associated with complementary functions such as a left-brain specialization for language and logic and a right-brain specialization for creativity and intuition. In fact, asymmetries are widespread among animals, and support the gradual evolution of asymmetrical functions such as language and tool use. Handedness and brain asymmetry are inborn and under partial genetic control, although the gene or genes responsible are not well established. Cognitive and emotional difficulties are sometimes associated with departures from the "norm" of right-handedness and left-brain language dominance, more often with the absence of these asymmetries than their reversal.

The cross-cultural nature of the relationship between schizotypy and mixed-handedness

Positive schizotypy is associated with non-right-handedness, which includes left- and mixed-handedness. However, because the underlying mechanisms might be different, it is important to examine whether both left- and mixed-handedness are associated with a high incidence of schizotypy. During 2009-2010, we used both the Perceptual Aberration Scale and Schizotypal Personality Questionnaire to assess 1315 undergraduate students in Taiwan for schizotypy and the Annett handedness questionnaire to assess handedness. Among the three-way classifications based on Annett's grouping, the fully left-handed group appeared to have the lowest score of positive schizotypy; next was the fully right-handed group and then the mixed-handed. Among the three-way classifications driven from cluster analysis, mixed-handers showed highest score of positive schizotypy. When handedness was treated continuously, both direction (e.g., Hand Preference Index) and consistency (e.g., Either hand use score) indicators were significantly correlated with schizotypy. The results of regression analyses showed that the quadratic handedness measure were negatively associated with schizotypy. The results remained similar after correcting for social pressure on left-handedness. In conclusion, the relationship between schizotypy and mixed-handedness appears to be cross-cultural. The dichotomous classification of handedness, right- vs. non-right-handedness, appears to be insufficient. Additional studies on the distinct mechanisms of mixed- and left-handedness are warranted.

Do shared etiological factors contribute to the relationship between sexual orientation and depression?

BACKGROUND

Gays, lesbians and bisexuals (i.e. non-heterosexuals) have been found to be at much greater risk for many psychiatric symptoms and disorders, including depression. This may be due in part to prejudice and discrimination experienced by non-heterosexuals, but studies controlling for minority stress, or performed in very socially liberal countries, suggest that other mechanisms must also play a role. Here we test the viability of common cause (shared genetic or environmental etiology) explanations of elevated depression rates in non-heterosexuals.

METHOD

A community-based sample of adult twins (n=9884 individuals) completed surveys investigating the genetics of psychiatric disorder, and were also asked about their sexual orientation. Large subsets of the sample were asked about adverse childhood experiences such as sexual abuse, physical abuse and risky family environment, and also about number of older brothers, paternal and maternal age, and number of close friends. Data were analyzed using the classical twin design.

RESULTS

Non-heterosexual males and females had higher rates of lifetime depression than their heterosexual counterparts. Genetic factors accounted for 31% and 44% of variation in sexual orientation and depression respectively. Bivariate analysis revealed that genetic factors accounted for a majority (60%) of the correlation between sexual orientation and depression. In addition, childhood sexual abuse and risky family environment were significant predictors of both sexual orientation and depression, further contributing to their correlation.

CONCLUSIONS

Non-heterosexual men and women had elevated rates of lifetime depression, partly due to shared etiological factors, although causality cannot be definitively resolved.

Sexual orientation and psychiatric vulnerability: a twin study of neuroticism and psychoticism

Recent evidence indicates that homosexuals and bisexuals are, on average, at greater risk for psychiatric problems than heterosexuals. It is assumed with some supporting evidence that prejudice often experienced by nonheterosexuals makes them more vulnerable to psychiatric disorder, but there has been no investigation of alternative explanations. Here we used Eysenck's Neuroticism and Psychoticism scales as markers for psychiatric vulnerability and compared heterosexuals with nonheterosexuals in a community-based sample of identical and nonidentical twins aged between 19 and 52 years (N = 4904). Firstly, we tested whether apparent sexual orientation differences in psychiatric vulnerability simply mirrored sex differences-for our traits, this would predict nonheterosexual males having elevated Neuroticism scores as females do, and nonheterosexual females having elevated Psychoticism scores as males do. Our results contradicted this idea, with nonheterosexual men and women scoring significantly higher on Neuroticism and Psychoticism than their heterosexual counterparts, suggesting an overall elevation of psychiatric risk in nonheterosexuals. Secondly, we used our genetically informative sample to assess the viability of explanations invoking a common cause of both nonheterosexuality and psychiatric vulnerability. We found significant genetic correlation between sexual orientation and both Neuroticism and Psychoticism, but no corresponding environmental correlations, suggesting that if there is a common cause of both nonheterosexuality and psychiatric vulnerability it is likely to have a genetic basis rather than an environmental basis.

Handedness, heritability, neurocognition and brain asymmetry in schizophrenia

Higher rates of non-right-handedness (i.e. left- and mixed-handedness) have been reported in schizophrenia and have been a centrepiece for theories of anomalous lateralization in this disorder. We investigated whether non-right-handedness is (i) more prevalent in patients as compared with unaffected siblings and healthy unrelated control participants; (ii) familial; (iii) associated with disproportionately poorer neurocognition; and (iv) associated with grey matter volume asymmetries. We examined 1445 participants (375 patients with schizophrenia, 502 unaffected siblings and 568 unrelated controls) using the Edinburgh Handedness Inventory, a battery of neuropsychological tasks and structural magnetic resonance imaging data. Patients displayed a leftward shift in Edinburgh Handedness Inventory laterality quotient scores as compared with both their unaffected siblings and unrelated controls, but this finding disappeared when sex was added to the model. Moreover, there was no evidence of increased familial risk for non-right-handedness. Non-right-handedness was not associated with disproportionate neurocognitive disadvantage or with grey matter volume asymmetries in the frontal pole, lateral occipital pole or temporal pole. Non-right-handedness was associated with a significant reduction in left asymmetry in the superior temporal gyrus in both patients and controls. Our data neither provide strong support for 'atypical' handedness as a schizophrenia risk-associated heritable phenotype nor that it is associated with poorer neurocognition or anomalous cerebral asymmetries.

Increased ratio of 2nd to 4th digit (2D:4D) in schizophrenia

Sex differences in the onset, epidemiology, clinical presentation and neuropathology of schizophrenia suggest that sexual dimorphism in brain development may be relevant to pathogenesis. Sex hormones, in particular testosterone, are considered to be crucial in brain development, but few investigations have examined the potential role of prenatal testosterone in schizophrenia. In this study, we examined a retrospective marker of prenatal testosterone release - 2D:4D finger length ratio (2D:4D), the relative length of 2nd to 4th digit, in 64 Asian patients with schizophrenia and 64 sex-matched controls. No significant difference in mean finger lengths was present, however 2D:4D ratio was significantly different between patients and controls. The effect was primarily seen in males consistent with a 'less masculinised' pattern and hypotheses suggesting that schizophrenia may be associated with an abnormality in prenatal circulating testosterone.

Psychosis and autism as diametrical disorders of the social brain

Autistic-spectrum conditions and psychotic-spectrum conditions (mainly schizophrenia, bipolar disorder, and major depression) represent two major suites of disorders of human cognition, affect, and behavior that involve altered development and function of the social brain. We describe evidence that a large set of phenotypic traits exhibit diametrically opposite phenotypes in autistic-spectrum versus psychotic-spectrum conditions, with a focus on schizophrenia. This suite of traits is inter-correlated, in that autism involves a general pattern of constrained overgrowth, whereas schizophrenia involves undergrowth. These disorders also exhibit diametric patterns for traits related to social brain development, including aspects of gaze, agency, social cognition, local versus global processing, language, and behavior. Social cognition is thus underdeveloped in autistic-spectrum conditions and hyper-developed on the psychotic spectrum.;>We propose and evaluate a novel hypothesis that may help to explain these diametric phenotypes: that the development of these two sets of conditions is mediated in part by alterations of genomic imprinting. Evidence regarding the genetic, physiological, neurological, and psychological underpinnings of psychotic-spectrum conditions supports the hypothesis that the etiologies of these conditions involve biases towards increased relative effects from imprinted genes with maternal expression, which engender a general pattern of undergrowth. By contrast, autistic-spectrum conditions appear to involve increased relative bias towards effects of paternally expressed genes, which mediate overgrowth. This hypothesis provides a simple yet comprehensive theory, grounded in evolutionary biology and genetics, for understanding the causes and phenotypes of autistic-spectrum and psychotic-spectrum conditions.

Magical ideation is related to questionnaire but not behavioural measures of handedness

Magical ideation has repeatedly been shown to be related to handedness, with mixed-handers exhibiting higher levels of magical thinking. However, most previous research has assessed hand preference with a questionnaire measure, leaving open the possibility that the correlation reflects some aspect of questionnaire-taking behaviour and not an underlying neuropsychological relationship. The present study addressed this issue by administering the Magical Ideation Scale (Eckblad & Chapman, 1983), the Waterloo Handedness Questionnaire-Revised (Elias, Bryden, & Bulman-Fleming, 1998), and a manual dot-filling task (Tapley & Bryden, 1985) as a behavioural measure of handedness to an undergraduate student sample. The expected relationship between magical ideation and handedness as assessed by the questionnaire was observed. However, magical ideation was not related to the behavioural measure of handedness. Results cast doubt on a neuropsychological interpretation of the relationship between handedness and magical ideation in sub-clinical populations.

LRRTM1 on chromosome 2p12 is a maternally suppressed gene that is associated paternally with handedness and schizophrenia

Left-right asymmetrical brain function underlies much of human cognition, behavior and emotion. Abnormalities of cerebral asymmetry are associated with schizophrenia and other neuropsychiatric disorders. The molecular, developmental and evolutionary origins of human brain asymmetry are unknown. We found significant association of a haplotype upstream of the gene LRRTM1 (Leucine-rich repeat transmembrane neuronal 1) with a quantitative measure of human handedness in a set of dyslexic siblings, when the haplotype was inherited paternally (P=0.00002). While we were unable to find this effect in an epidemiological set of twin-based sibships, we did find that the same haplotype is overtransmitted paternally to individuals with schizophrenia/schizoaffective disorder in a study of 1002 affected families (P=0.0014). We then found direct confirmatory evidence that LRRTM1 is an imprinted gene in humans that shows a variable pattern of maternal downregulation. We also showed that LRRTM1 is expressed during the development of specific forebrain structures, and thus could influence neuronal differentiation and connectivity. This is the first potential genetic influence on human handedness to be identified, and the first putative genetic effect on variability in human brain asymmetry. LRRTM1 is a candidate gene for involvement in several common neurodevelopmental disorders, and may have played a role in human cognitive and behavioral evolution.

Mixed-handedness is associated with the reporting of psychotic-like beliefs in a non-clinical Italian sample

Atypical handedness has been repeatedly reported in schizophrenia, with quantitative review of evidence showing an increase of non-right-handedness in patients diagnosed with schizophrenia. Mixed-handedness is also higher among non-clinical people scoring high on questionnaires aimed at measuring psychosis-proneness. However, the greatest part of information on non-clinical samples came from samples collected in North America or in the UK: differences by countries in the socio-cultural pressure to use the right hand could influence the results. In this study 604 Italian non-clinical participants (248 males, 41.1%; 356 females, 58.9%; mean age=34.5+/-11.9) completed the Annett Hand Preference Questionnaire (HPQ), the General Health Questionnaire (GHQ), and the Peters et al. Delusions Inventory (PDI). In the sample, 527 subjects (87.3%) were classified on the HPQ as right-handed, 53 (8.8%) were classified as mixed-handed, and 24 (4.0%) were classified as left-handed. Mixed-handed scored statistically higher on the PDI than the right-handed and left-handed, but right-handed and left-handed did not differ from each other on a statistical ground. The difference by handedness was specific for PDI, since scores on the GHQ-12 did not differ by handedness group. The links between mixed-handedness and psychosis-proneness in non-clinical samples are a reliable finding, deserving further investigation as a model for the risk of schizophrenia.

Heritability and linkage analysis of hand, foot, and eye preference in Mexican Americans

Functional lateralities are of interest due to their relationship with cerebral lateralisation and language development. However, genes influencing sidedness remain elusive. We measured direction and consistency of hand, foot, and eye preference in 584 Mexican-Americans from families participating in the San Antonio Family Diabetes/Gallbladder Study. Using maximum-likelihood-based variance components methods, we estimated weak (.11 <or= h2<or=.17) but significant heritability for foot preference, eye preference, several hand preferences (writing, drawing, throwing, using scissors, using spoon, striking match), and a composite hand preference trait. Self-reported handedness was significantly heritable (h2=.57), whereas hand preference for opening a box or using a toothbrush or knife was not. Many trait pairs had significant genetic correlations, and all had significant environmental correlations. Using genome-wide multipoint linkage screens using 382 highly informative autosomal STR markers, we identified suggestive linkage signals for drawing (LOD 2.10) and writing (LOD 2.00) hand preference on chromosome 12q21-23, in the region flanked by markers D12S1300 and PAH. A suggestive signal (LOD 2.46) for eye preference occurred on chromosome 22pter, near marker D22S420. No obvious candidate genes occur in these regions. Our results indicate that genes are an important component of side preferences, and suggest chromosomal regions for further investigation.

Is mixed-handedness a marker of treatment response in posttraumatic stress disorder?: a pilot study

Recent studies suggest that mixed-handedness is a risk factor for posttraumatic stress disorder (PTSD). This study examined whether mixed-handed veterans with combat-related PTSD respond more poorly to psychosocial treatment. Consistency of hand preference was assessed in 150 Vietnam combat veterans with PTSD using the Edinburgh Handedness Inventory (R. C. Oldfield, 1971). Growth modeling analyses using Mplus (L. K. Muthén & B. Muthén, 2002) identified that PTSD veterans with mixed-handedness reported significantly less treatment improvement on the PTSD Checklist (F. W. Weathers, B. T. Litz, D. S. Herman, J. A. Huska, & T. M. Keane, 1993) than did veterans with consistent handedness. These data suggest that mixed-handedness is associated with poorer PTSD treatment response. Several possible explanations for this finding are discussed.

Verbal creativity and schizotypal personality in relation to prefrontal hemispheric laterality: a behavioral and near-infrared optical imaging study

Although anecdotal and correlational results have suggested a reliable relationship between creativity and psychosis, few studies have examined this relationship using empirical methods. In addition, little is known about the neural substrates of creative thinking. We investigated the creative thinking process in relation to schizotypal personality, schizophrenia and prefrontal hemispheric laterality using behavioral and near-infrared optical spectroscopy (NIRS) methods. Schizophrenic, psychometrically ascertained schizotypal, and healthy control subjects (all right-handed) participated in a novel "alternate uses" task designed to assess divergent thinking (DT) ability. The DT task required subjects to generate "uses" for conventional and ambiguous objects. Prefrontal activity was measured using NIRS while subjects were engaged in DT vs. a cognitive control task in a subset of the subjects. Behavioral data indicated that schizotypes had enhanced DT ability compared with schizophrenic and control subjects, who showed similar performance overall. NIRS data showed that DT was associated with bilateral prefrontal cortex (PFC) activation, but the right PFC particularly contributed to the enhanced creative thinking in psychometric schizotypes compared with the other two groups. Thus, creative thinking seems to robustly recruit bilateral PFC, but it is the right PFC that is preferentially activated in schizotypes in relation to their enhanced DT.

Handedness in children of schizophrenic parents: data from three high-risk studies

This is the first report of data analyses from a consortium of longitudinal genetic-risk studies on offspring of schizophrenic parents (CLOSSER) who were followed from birth or mid-childhood to their early 20's or considerably older ages. Three of the CLOSSER studies provide data to enable us to address long-persisting questions in the schizophrenia literature concerning possible atypicality of hand dominance associated with the illness. Handedness, used as a proxy for cerebral lateralization, is a topic of considerable importance because of its potential to reveal mechanisms in the underlying pathophysiology of schizophrenia. We examine agreement among the CLOSSER studies with respect to possible deviance in handedness in subjects with schizophrenic parents (high-risk individuals) and specifically in those who have gone on to develop adult schizophrenia, compared with other subjects of these studies. Possible developmental delay in age at lateralization is also considered.

Handedness in schizophrenia: a quantitative review of evidence

OBJECTIVE

The prevalence of various anomalous handedness subtypes in schizophrenia patients remains ambiguous. Although current literature favours the notion that the shift in lateral preferences seen is because of an increase of mixed-handedness, several studies suggest that exclusive left handedness is more prevalent than in the general population.

METHOD

Over 40 studies with reported prevalence data on various handedness subtypes in a schizophrenia population were evaluated by meta-analysis. Combined odds ratios for the three common handedness subtypes (left, mixed, and right) were separately calculated.

RESULTS

Each of the three atypical hand dominance patterns were significantly greater in schizophrenia patients than in control subjects, showing that the leftward shift in handedness distribution is not entirely because of an increase in mixed-handedness alone.

CONCLUSION

An increase of exclusive left-handedness is at variance with the prevailing assertion that the handedness shift in schizophrenia patients is because of a diffuse and bilateral hemispheric insult.

Strong mixed-handedness in schizophrenia

There is still considerable discussion of whether schizophrenia is a lateralized brain disorder. In fact, schizophrenic patients appear to exhibit a shift away from dexterity, as confirmed by the majority of the 23 publications dealing with this question (14 positive, seven null, two paradoxical). However, quite a few of these positive studies have distinguished between left-handedness and mixed-handedness (MH), thus lacking specificity. Whereas prior studies failed to specify schizophrenic MH, we could observe a significant relationship between strong MH and schizophrenia in male patients in a relatively small group due to sex differentiation and accurate application of Annett's hand preference questionnaire.

Is lateral bias anomalous in early-onset schizophrenia? Selected comparisons with normal populations

The aim of this study was to investigate lateral bias in patients with early-onset schizophrenia. Hand, eye, and foot preferences and relative hand skill were examined in early-onset patients (n=44) and matched controls (n=39), and were compared with population estimates. Patients demonstrated a significant excess in mixed handedness (20.5% vs. 8.5%) relative to population estimates and reduced relative hand skill on a pegboard task compared with controls. Left eye preference was significantly less common in schizophrenic patients relative to population estimates. Crossed eye-hand and eye-foot preferences were not significantly increased in the patient group as a whole but were present, respectively, in four of nine and five of nine mixed-handed patients but in none of five mixed-handed controls. These findings are consistent with the view that lateralisation is anomalous in schizophrenia early in the course of illness.