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.

Hand Preference in Stuttering: Meta-Analyses.

Reduced hemispheric asymmetries, as well as their behavioral manifestation in the form of atypical handedness (i.e., non-right, left-, or mixed-handedness), are linked to neurodevelopmental disorders, such as autism spectrum disorder, and several psychiatric disorders, such as schizophrenia. One neurodevelopmental disorder that is associated with reduced hemispheric asymmetries, but for which findings on behavioral laterality are conflicting, is stuttering. Here, we report a series of meta-analyses of studies that report handedness (assessed as hand preference) levels in individuals who stutter (otherwise healthy) compared to controls. For this purpose, articles were identified via a search in PubMed, Scopus, and PsycInfo (13 June 2023). On the basis of k = 52 identified studies totaling n = 2590 individuals who stutter and n = 17,148 controls, five random effects meta-analyses were conducted: four using the odds ratio [left-handers (forced choice); left-handers (extreme); mixed-handers; non-right-handers vs. total)] and one using the standardized difference in means as the effect size. We did not find evidence of a left (extreme)- or mixed-handedness difference or a difference in mean handedness scores, but evidence did emerge, when it came to left-handedness (forced-choice) and (inconclusively for) non-right-handedness. Risk-of-bias analysis was not deemed necessary in the context of these meta-analyses. Differences in hand skill or strength of handedness could not be assessed as no pertinent studies were located. Severity of stuttering could not be used s a moderator, as too few studies broke down their data according to severity. Our findings do not allow for firm conclusions to be drawn on whether stuttering is associated with reduced hemispheric asymmetries, at least when it comes to their behavioral manifestation.

A meta-analysis of the line bisection task in children.

Meta-analyses have shown subtle, group-level asymmetries of spatial attention in adults favouring the left hemispace (pseudoneglect). However, no meta-analysis has synthesized data on children. We performed a random-effects meta-analysis of spatial biases in children aged ≤16 years. Databases (PsycINFO, Web of Science & Scopus) and pre-print servers (bioRxiv, medRxiv & PsyArXiv) were searched for studies involving typically developing children with a mean age of ≤16, who were tested using line bisection. Thirty-three datasets, from 31 studies, involving 2101 children, were included. No bias was identified overall, but there was a small leftward bias in a subgroup where all children were aged ≤16. Moderator analysis found symmetrical neglect, with right-handed actions resulting in right-biased bisections, and left-handed actions in left-biased bisections. Bisections were more leftward in studies with a higher percentage of boys relative to girls. Mean age, hand preference, and control group status did not moderate biases, and there was no difference between children aged ≤7 and ≥7 years, although the number of studies in each moderator analysis was small. There was no evidence of small study bias. We conclude that pseudoneglect may be present in children but is dependent on individual characteristics (sex) and/or task demands (hand used).Registration: Open Science Framework (https://osf.io/n68fz/).

Cerebral laterality of writing in right- and left-handers: A functional transcranial Doppler ultrasound study.

The cerebral lateralization of written language has received very limited research attention in comparison to the wealth of studies on the cerebral lateralization of oral language. The purpose of the present study was to further our understanding of written language lateralization, by elucidating the relative contribution of language and motor functions. We compared written word generation with a task that has equivalent visuomotor demands but does not include language: the repeated drawing of symbols. We assessed cerebral laterality using functional transcranial Doppler ultrasound (fTCD), a non-invasive, perfusion-sensitive neuroimaging technique in 23 left- and 31 right-handed participants. Findings suggest that the linguistic aspect of written word generation recruited more left-hemispheric areas during writing, in right-handers compared to left-handers. This difference could be explained by greater variability in cerebral laterality patterns within left-handers or the possibility that the areas subserving language in left-handers are broader than in right-handers. Another explanation is that the attentional demands of the more novel symbol copying task (compared to writing) contributed more right-hemispheric activation in right-handers, but this could not be captured in left-handers due to ceiling effects. Future work could investigate such attentional demands using both simple and complex stimuli in the copying condition.

A Meta-Analysis of Line Bisection and Landmark Task Performance in Older Adults.

Young adults exhibit a small asymmetry of visuospatial attention that favours the left side of space relative to the right (pseudoneglect). However, it remains unclear whether this leftward bias is maintained, eliminated or shifted rightward in older age. Here we present two meta-analyses that aimed to identify whether adults aged ≥50 years old display a group-level spatial attention bias, as indexed by the line bisection and the landmark tasks. A total of 69 datasets from 65 studies, involving 1654 participants, were analysed. In the meta-analysis of the line bisection task (n = 63), no bias was identified for studies where the mean age was ≥50, but there was a clear leftward bias in a subset where all individual participants were aged ≥50. There was no moderating effect of the participant's age or sex, line length, line position, nor the presence of left or right cues. There was a small publication bias in favour of reporting rightward biases. Of note, biases were slightly more leftward in studies where participants had been recruited as part of a stand-alone older group, compared to studies where participants were recruited as controls for a clinical study. Similarly, no spatial bias was observed in the meta-analysis of the landmark task, although the number of studies included was small (n = 6). Overall, these results indicate that over 50s maintain a group-level leftward bias on the line bisection task, but more studies are needed to determine whether this bias can be modulated by stimulus- or state-dependent factors.

Handedness in ADHD: Meta-Analyses.

Meta-analyses have shown that several neurodevelopmental and psychiatric disorders, such as autism spectrum disorder and schizophrenia, are associated with a higher prevalence of atypical (left-, non-right-, or mixed-) handedness. One neurodevelopmental disorder for which this association is unclear is attention deficit hyperactivity disorder (ADHD). Here, some empirical studies have found evidence for a higher prevalence of atypical handedness in individuals with ADHD compared to neurotypical individuals. However, other studies failed to establish such an association. Therefore, meta-analytic integration is critical to estimate whether or not there is an association between handedness and ADHD. We report the results of three meta-analyses (left-, mixed-, and non-right-handedness) comparing handedness in individuals with ADHD to controls (typically developing individuals). The results show evidence of a trend towards elevated levels of atypical handedness when it comes to differences in left- and mixed-handedness (p = 0.09 and p = 0.07, respectively), but do show clear evidence of elevated levels of non-right-handedness between individuals with ADHD and controls (p = 0.02). These findings are discussed in the context of the hypothesis that ADHD is a disorder in which mostly right-hemispheric brain networks are affected. Since right-handedness represents a dominance of the left motor cortex for fine motor behavior, such as writing, as well as a left-hemispheric dominance for language functions, and about 90% of individuals are right-handers, this hypothesis might explain why there is not stronger evidence for an association of left-handedness with ADHD. We suggest that the mechanisms involved in the pathogenesis of ADHD might show an overlap with the mechanisms involved in handedness strength, but not handedness direction.

Investigating the feasibility of MePlusMe, an online intervention to support mental health, well-being, and study skills in higher education students.

INTRODUCTION: While there are several web-based mental health interventions, few target higher education (HE) students. Importantly, more research is needed to establish their effectiveness. Here, we provide a pragmatic evaluation of an online intervention (MePlusMe) specifically designed to improve the mental health, well-being, and study skills of HE students. METHODS: In accordance with the published protocol for a feasibility study, we recruited a convenience sample of 137 HE students to participate in an eight-week intervention, with 26 participants retained at week 8. Validated measures of mood (depression and anxiety), well-being, and self-efficacy were collected at baseline, 2, 4, and 8 weeks, alongside two feedback forms assessing design and functionality (baseline) and engagement (week 4 and 8). RESULTS: We observed significant reductions in levels of anxiety and depression as well as increases in well-being, but no changes in self-efficacy. Participants rated the system design and functionality positively and qualitative findings indicated high levels of satisfaction with MePlusMe. DISCUSSION: Findings support both the acceptability and the effectiveness of MePlusMe. Nonetheless, modest retention rates limit the precision and generalisability of these findings. Further investigation should ascertain optimal duration of engagement, most acceptable means of outcome assessment, and further detail about obstacles to utilisation.

Hand preference and Mathematical Learning Difficulties: New data from Greece, the United Kingdom, and Germany and two meta-analyses of the literature.

Increased rates of atypical handedness are observed in neurotypical individuals who are low-performing in mathematical tasks as well as in individuals with special educational needs, such as dyslexia. This is the first investigation of handedness in individuals with Mathematical Learning Difficulties (MLD). We report three new studies (N = 134; N = 1,893; N = 153) and two sets of meta-analyses (22 studies; N = 3,667). No difference in atypical hand preference between MLD and Typically Achieving (TA) individuals was found when handedness was assessed with self-report questionnaires, but weak evidence of a difference was found when writing hand was the handedness criterion in Study 1 (p = .049). Similarly, when combining data meta-analytically, no hand preference differences were detected. We suggest that: (i) potential handedness effects require larger samples, (ii) direction of hand preference is not a sensitive enough measure of handedness in this context, or that (iii) increased rates of atypical hand preference are not associated with MLD. The latter scenario would suggest that handedness is specifically linked to language-related conditions rather than conditions related to cognitive abilities at large. Future studies need to consider hand skill and degree of hand preference in MLD.

Universal Patterns in Color-Emotion Associations Are Further Shaped by Linguistic and Geographic Proximity.

Many of us "see red," "feel blue," or "turn green with envy." Are such color-emotion associations fundamental to our shared cognitive architecture, or are they cultural creations learned through our languages and traditions? To answer these questions, we tested emotional associations of colors in 4,598 participants from 30 nations speaking 22 native languages. Participants associated 20 emotion concepts with 12 color terms. Pattern-similarity analyses revealed universal color-emotion associations (average similarity coefficient r = .88). However, local differences were also apparent. A machine-learning algorithm revealed that nation predicted color-emotion associations above and beyond those observed universally. Similarity was greater when nations were linguistically or geographically close. This study highlights robust universal color-emotion associations, further modulated by linguistic and geographic factors. These results pose further theoretical and empirical questions about the affective properties of color and may inform practice in applied domains, such as well-being and design.

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.

Paw preferences in cats and dogs: Meta-analysis.

Predator-prey relationships have been suggested to be one of the primary evolutionary factors driving the development of functional hemispheric asymmetries. However, lateralization in many predator species is not well understood and existing studies often are statistically underpowered due to small sample sizes and they moreover show conflicting results. Here, we statistically integrated findings on paw preferences in cats and dogs, two predator species within the Carnivora order that are commonly kept as pets in many societies around the globe. For both species, there were significantly more lateralized than non-lateralized animals. We found that 78% of cats and 68% of dogs showed either left- or right-sided paw preference. Unlike humans, neither dogs nor cats showed a rightward paw preference on the population level. For cats, but not dogs, we found a significant sex difference, with female animals having greater odds of being right-lateralized compared to male animals.

Elevated Levels of Atypical Handedness in Autism: Meta-Analyses.

An elevated prevalence of atypical handedness (left-, mixed-, or non-right-handedness) has been repeatedly reported in individuals with Autism Spectrum Disorder (ASD) compared to typically developing individuals. However, the exact magnitude of this difference as well as the presence of possible moderating factors remains unknown. Here, we present three sets of meta-analyses of studies that assessed the handedness prevalence among individuals with ASD, totaling 1199 individuals (n = 723 individuals with ASD and n = 476 typically developing individuals). Meta-analysis set 1 found that individuals with ASD are 3.48, 2.49, and 2.34 times more likely to be non-right-handed, left-handed, and mixed-handed compared to typically developing individuals, respectively. Meta-analysis set 2 found a 45.4%, 18.3%, and 36.1% prevalence of non-right-handedness, left-handedness, and mixed-handedness, respectively, amongst individuals with ASD. The classification of handedness, the instrument used to measure handedness, and the main purpose of the study were found to moderate the findings of meta-analysis set 2. Meta-analysis set 3 revealed a trend towards weaker handedness for individuals with ASD. The elevated levels of atypical handedness in individuals with ASD could be attributed to atypicalities in cerebral structure and lateralization for language in individuals with ASD.

Salivary testosterone levels are unrelated to handedness or cerebral lateralization for language.

Behavioural and cerebral lateralization are thought to be controlled, at least in part, by prenatal testosterone (T) levels, explaining why sex differences are found in both laterality traits. The present study investigated hormonal effects on laterality using adult salivary T levels, to explore the adequacy of competing theories: the Geschwind, Behan and Galaburda, the callosal, and the sexual differentiation hypotheses. Sixty participants (15 right-handers and 15 left-handers of each sex) participated. Behavioural lateralization was studied by means of hand preference tests (i.e., the Edinburgh Handedness Inventory and the Quantification of Hand Preference test) and a hand skill test (i.e., the Peg-Moving test) whereas cerebral lateralization for language was studied using the Consonant-Vowel Dichotic Listening test and the Visual Half-Field Lexical Decision test. Salivary T and cortisol (C) concentrations were measured by luminescence immunoassay. Canonical correlations did not reveal significant relationships between T levels and measures of hand preference, hand skill, or language laterality. Thus, our findings add to the growing literature showing no relationship between T concentrations with behavioural or cerebral lateralization. It is claimed that prenatal T is not a major determinant of individual variability in either behavioural or cerebral lateralization.

Clinical implications of brain asymmetries.

No two human brains are alike, and with the rise of precision medicine in neurology, we are seeing an increased emphasis on understanding the individual variability in brain structure and function that renders every brain unique. Functional and structural brain asymmetries are a fundamental principle of brain organization, and recent research suggests substantial individual variability in these asymmetries that needs to be considered in clinical practice. In this Review, we provide an overview of brain asymmetries, variations in such asymmetries and their relevance in the clinical context. We review recent findings on brain asymmetries in neuropsychiatric and neurodevelopmental disorders, as well as in specific learning disabilities, with an emphasis on large-scale database studies and meta-analyses. We also highlight the relevance of asymmetries for disease symptom onset in neurodegenerative diseases and their implications for lateralized treatments, including brain stimulation. We conclude that alterations in brain asymmetry are not sufficiently specific to act as diagnostic biomarkers but can serve as meaningful symptom or treatment response biomarkers in certain contexts. On the basis of these insights, we provide several recommendations for neurological clinical practice.

A comparative analysis of colour-emotion associations in 16-88-year-old adults from 31 countries.

As people age, they tend to spend more time indoors, and the colours in their surroundings may significantly impact their mood and overall well-being. However, there is a lack of empirical evidence to provide informed guidance on colour choices, irrespective of age group. To work towards informed choices, we investigated whether the associations between colours and emotions observed in younger individuals also apply to older adults. We recruited 7393 participants, aged between 16 and 88 years and coming from 31 countries. Each participant associated 12 colour terms with 20 emotion concepts and rated the intensity of each associated emotion. Different age groups exhibited highly similar patterns of colour-emotion associations (average similarity coefficient of .97), with subtle yet meaningful age-related differences. Adolescents associated the greatest number but the least positively biased emotions with colours. Older participants associated a smaller number but more intense and more positive emotions with all colour terms, displaying a positivity effect. Age also predicted arousal and power biases, varying by colour. Findings suggest parallels in colour-emotion associations between younger and older adults, with subtle but significant age-related variations. Future studies should next assess whether colour-emotion associations reflect what people actually feel when exposed to colour.

Measuring hand preference: a comparison among different response formats using a selected sample.

Hand preference (HP) is a major behavioural variable for inferring individual differences in neurological organisation. Yet, despite the extensive use of HP measures for both research and clinical purposes, there is little research on the properties of the structural features of HP questionnaires, the most common method of HP measurement. We study here the effects of different response formats of HP questionnaires on participants' responses. A total of 200 volunteers (100 left-handers, 50 male; 100 right-handers, 50 male) completed two versions of a composite HP questionnaire containing the items of the Annett, Edinburgh, Healy, and Waterloo instruments, one with a binary response format and the other with a 5-point graded response format. The tendency towards extreme responses and the mapping between a graded either response and a binary left/right response were investigated. It was found that both patterns were significantly influenced by participant handedness, but not by sex. Finally, in terms of the overall ordering of participants by HP measures, considerable consistency was found across questionnaire content and response format.

Handedness in post-traumatic stress disorder: A meta-analysis.

The main objective of this meta-analysis was to investigate handedness in post-traumatic stress disorder on a meta-analytical level. For this purpose, articles were identified via a search in PubMed, PsychInfo, PubPsych, ResearchGate, and Google Scholar. Studies reporting findings relating to handedness in PTSD patients and healthy controls were considered eligible. In total, k = 14 studies with an overall N of 2939 (747 PTSD patients and 2192 controls) were included in the study. Random-effects meta-analyses, as well as robust Bayes meta-analyses (RoBMA), were conducted for three comparisons: (a) non-right-handedness, (b) left-handedness, and (c) mixed-handedness. Results showed significantly higher frequencies of non-right-handedness (odds ratio = 1.81) and mixed-handedness (odds ratio = 2.42) in PTSD patients compared to controls. No differences were found for left-handedness. This specific effect of mixed-handedness is in line with findings for other disorders, such as schizophrenia. Future studies should investigate common neurodevelopmental origins for the relationship between mixed-handedness and psychopathology and aim at investigating both handedness direction and handedness strength.

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.

Handedness and midsagittal corpus callosum morphology: a meta-analytic evaluation.

Following a series of seminal studies in the 1980s, left or mixed hand preference is widely thought to be associated with a larger corpus callosum than right handedness, influencing the interpretation of findings and various theories related to interhemispheric processing, brain lateralisation, and hand preference. Recent reviews, however, find inconsistencies in the literature and cast doubt on the existence of such an association. The present study was conducted to clarify the relationship between hand preference and callosal morphology in a series of meta-analyses. For this purpose, articles were identified via a search in PubMed and Web Of Science databases. Studies reporting findings relating to handedness (assessed as hand preference) and corpus-callosum morphology in healthy participants were considered eligible. On the basis of a total of k = 24 identified studies and databases, random-effects meta-analyses were conducted considering four different group comparisons: (a) dominantly right- (dRH) and left-hand preference (dLH), (b) consistent right (cRH) and non-cRH preference, (c) cRH with mixed-hand preference (MH), and (d) cRH with consistent left-hand hand preference (cLH). For none of these meta-analyses did we find a significant effect of hand preference, and narrow confidence intervals suggest that the existence of population effects larger than 1% explained variance could be excluded. For example, considering the comparison of dRH and dLH (k = 14 studies; 1910 dRH and 646 dLH participants) the mean effect size was Hedge's g = 0.016 (95% confidence interval: - 0.12 to 0.15; explained variance: < 0.001%). Thus, the common practice of assuming an increase in callosal connectivity based on mixed or left hand preference is likely invalid.

Handedness in twins: meta-analyses.

BACKGROUND: In the general population, 10.6% of people favor their left hand over the right for motor tasks. Previous research suggests higher prevalence of atypical (left-, mixed-, or non-right-) handedness in (i) twins compared to singletons, and in (ii) monozygotic compared to dizygotic twins. Moreover, (iii) studies have shown a higher rate of handedness concordance in monozygotic compared to dizygotic twins, in line with genetic factors playing a role for handedness. METHODS: By means of a systematic review, we identified 59 studies from previous literature and performed three sets of random effects meta-analyses on (i) twin-to-singleton Odds Ratios (21 studies, n = 189,422 individuals) and (ii) monozygotic-to-dizygotic twin Odds Ratios (48 studies, n = 63,295 individuals), both times for prevalence of left-, mixed-, and non-right-handedness. For monozygotic and dizygotic twin pairs we compared (iii) handedness concordance Odds Ratios (44 studies, n = 36,217 twin pairs). We also tested for potential effects of moderating variables, such as sex, age, the method used to assess handedness, and the twins' zygosity. RESULTS: We found (i) evidence for higher prevalence of left- (Odds Ratio = 1.40, 95% Confidence Interval = [1.26, 1.57]) and non-right- (Odds Ratio = 1.36, 95% Confidence Interval = [1.22, 1.52]), but not mixed-handedness (Odds Ratio = 1.08, 95% Confidence Interval = [0.52, 2.27]) among twins compared to singletons. We further showed a decrease in Odds Ratios in more recent studies (post-1975: Odds Ratio = 1.30, 95% Confidence Interval = [1.17, 1.45]) compared to earlier studies (pre-1975: Odds Ratio = 1.90, 95% Confidence Interval = [1.59-2.27]). While there was (ii) no difference between monozygotic and dizygotic twins regarding prevalence of left- (Odds Ratio = 0.98, 95% Confidence Interval = [0.89, 1.07]), mixed- (Odds Ratio = 0.96, 95% Confidence Interval = [0.46, 1.99]), or non-right-handedness (Odds Ratio = 1.01, 95% Confidence Interval = [0.91, 1.12]), we found that (iii) handedness concordance was elevated among monozygotic compared to dizygotic twin pairs (Odds Ratio = 1.11, 95% Confidence Interval = [1.06, 1.18]). By means of moderator analyses, we did not find evidence for effects of potentially confounding variables. CONCLUSION: We provide the largest and most comprehensive meta-analysis on handedness in twins. Although a raw, unadjusted analysis found a higher prevalence of left- and non-right-, but not mixed-handedness among twins compared to singletons, left-handedness was substantially more prevalent in earlier than in more recent studies. The single large, recent study which included birth weight, Apgar score and gestational age as covariates found no twin-singleton difference in handedness rate, but these covariates could not be included in the present meta-analysis. Together, the secular shift and the influence of covariates probably make it unsafe to conclude that twinning has a genuine relationship to handedness.