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

Left-handedness in otolaryngology, who is right?

Objectives

This study aimed to ascertain the prevalence of left-handedness (LH) among otolaryngology-head and neck surgery (ORLHN) practitioners, investigate dexterity's impact on LH trainees, and identify common patterns in their training to improve the training experience.

Methods

A web-based survey was distributed anonymously via email to members of the Saudi Otorhinolaryngology Society. The survey targeted ORLHN attending consultants, board-certified registrars, and current residents. It consisted of three sections: the first focused on the experience of attending consultants in training LH individuals, the second investigated common maneuvers employed by rhinologists, and the third explored the experiences and impacts reported by LH trainees.

Results

The study included 174 participants, and found a 13.2% LH prevalence among them. Rhinologists showed disparities, with 50% advising trainees to stand on the left side of the bed and use their left hand for the scope, whereas the other half asked otherwise. Additionally, 94.4% of the participants had not encountered any courses specifically tailored for LH trainees. Among LH trainees, 57% and 41% reported difficulties in learning and performing side-specific procedures such as functional endoscopic sinus surgery and endoscopic septoplasty, respectively, often attempting to switch to their nondominant hand, and feeling disadvantaged due to their laterality.

Conclusions

Left-handedness presents challenges for both LH trainees and their trainers in surgical specialties, particularly in ORLHN, in which specific positioning and instruments are crucial to gain access to the desired surgical field. Despite these challenges, there is insufficient support for LH individuals. We recommend encouraging LH trainees to openly disclose and discuss their left-handedness, provide them with mentors, establish standardized operating room setups and techniques, supply appropriate instruments, and demonstrate flexibility in accommodating their needs.

Level of evidence

Level 5.

Is it possible to identify physical-motor profiles of preschool children on their association with selected biosocial factors?

Biosocial factors play a crucial role in the physical-motor development (PMD) of children during the preschool age. The present study aims to identify physical-motor profiles throughout preschool age (3-6 years) and explore associations between profiles and selected biosocial factors such as age, sex, prematurity, weight, height, BMI, and participation in extracurricular physical activities. Data from 412 typically developing children (46.6% girls and 53.4% boys), aged 35-71 months (M = 51.21, SD = 10.47) was collected using the Psychomotor Activities Checklist and specifically the scale of Psycho-Motor Aspects. Cluster analysis made it possible to define four different childhood PMD profiles. High PMD; High PMD except left laterality; medium-low PMD; and low PMD. High PMD profile includes older children, with anthropometric measurements closer to the WHO recommendations, fewer preterm children, and greater participation in extracurricular physical activities. Low PMD profile includes younger children, with weight slightly above and height slightly below the WHO recommendations and low participation in extracurricular physical activities. This study allows us to identify specific trends that may be decisive for the motor development of children throughout preschool age, highlighting selected biological variables and participation in extracurricular physical activities.

No link between handedness and spatial navigation: evidence from over 400 000 participants in 41 countries

There is an active debate concerning the association of handedness and spatial ability. Past studies used small sample sizes. Determining the effect of handedness on spatial ability requires a large, cross-cultural sample of participants and a navigation task with real-world validity. Here, we overcome these challenges via the mobile app Sea Hero Quest. We analysed the navigation performance from 422 772 participants from 41 countries and found no reliable evidence for any difference in spatial ability between left- and right-handers across all countries. A small but growing gap in performance appears for participants over 64 years old, with left-handers outperforming right-handers. Further analysis, however, suggests that this gap is most likely due to selection bias. Overall, our study clarifies the factors associated with spatial ability and shows that left-handedness is not associated with either a benefit or a deficit in spatial ability.

Carving the Biodevelopment of Same-Sex Sexual Orientation at Its Joints

Sexual orientation is a core aspect of human experience and understanding its development is fundamental to psychology as a scientific discipline. Biological perspectives have played an important role in uncovering the processes that contribute to sexual orientation development. Research in this field has relied on a variety of populations, including community, clinical, and cross-cultural samples, and has commonly focused on female gynephilia (i.e., female sexual attraction to adult females) and male androphilia (i.e., male sexual attraction to adult males). Genetic, hormonal, and immunological processes all appear to influence sexual orientation. Consistent with biological perspectives, there are sexual orientation differences in brain development and evidence indicates that similar biological influences apply across cultures. An outstanding question in the field is whether the hypothesized biological influences are all part of the same process or represent different developmental pathways leading to same-sex sexual orientation. Some studies indicate that same-sex sexually oriented people can be divided into subgroups who likely experienced different biological influences. Consideration of gender expression in addition to sexual orientation might help delineate such subgroups. Thus, future research on the possible existence of such subgroups could prove to be valuable for uncovering the biological development of sexual orientation. Recommendations for such future research are discussed.

Is Histamine and Not Acetylcholine the Missing Link between ADHD and Allergies? Speer Allergic Tension Fatigue Syndrome Re-Visited

Speer allergic tension-fatigue syndrome (SATFS) is a classic allergy syndrome characterized by allergy-like symptoms, muscle tension, headaches, chronic fatigue, and other particular behaviors that were initially described in the fifties. The particular behaviors displayed include symptoms such as hyperkinesis, hyperesthesia (i.e., insomnia), restlessness, and distractibility, among others. Interestingly, these symptoms are very similar to descriptions of attention deficit hyperactivity disorder (ADHD), the most prevalent neurodevelopmental disorder worldwide, which is characterized by inattention, hyperactivity, and impulsivity. The clinical description of SATFS precedes the nomination of ADHD in 1960 by Stella Chess. In this conceptual paper, we stress that there is a gap in the research on the relationship between ADHD and allergic pathologies. The hypotheses of this conceptual paper are (1) SATFS is probably one of the first and best historical descriptions of ADHD alongside a common comorbidity (allergy) displayed by these patients; (2) SATFS (ADHD) is a systemic disease that includes both somatic and behavioral manifestations that may influence each other in a bidirectional manner; (3) The role of neuroinflammation and histamine is key for understanding the pathophysiology of ADHD and its frequent somatic comorbidities; (4) The deficiency of the diamine oxidase (DAO) enzyme, which metabolizes histamine extracellularly, may play a role in the pathophysiology of ADHD. Decreased DAO activity may lead to an accumulation of histamine, which could contribute to core ADHD symptoms and comorbid disorders. Further empirical studies are needed to confirm our hypotheses.

Language and reading impairments are associated with increased prevalence of non-right-handedness

Handedness has been studied for association with language-related disorders because of its link with language hemispheric dominance. No clear pattern has emerged, possibly because of small samples, publication bias, and heterogeneous criteria across studies. Non-right-handedness (NRH) frequency was assessed in N = 2503 cases with reading and/or language impairment and N = 4316 sex-matched controls identified from 10 distinct cohorts (age range 6-19 years old; European ethnicity) using a priori set criteria. A meta-analysis (Ncases  = 1994) showed elevated NRH % in individuals with language/reading impairment compared with controls (OR = 1.21, CI = 1.06-1.39, p = .01). The association between reading/language impairments and NRH could result from shared pathways underlying brain lateralization, handedness, and cognitive functions.

Handedness and 23 Early Life Characteristics in 37,495 Dutch Twins

In studies of singletons, a range of early-life characteristics have been reported to be associated with handedness, but some of these associations have failed to replicate. We examined associations between 23 early life characteristics with handedness in a large sample of 37,495 5-year-old twins. We considered three definitions of handedness: left-handedness (LH), mixed-handedness (MH), and non-right-handedness (NRH). Our main aim was to test whether the associations with sex, birth weight, gestational age, and season of birth - as reported in singletons - replicate in twins, and to examine twin-specific variables, including zygosity, chorionicity, birth order, and intertwin delivery time. Compared to previously published data from adults born as singletons (7.23%), the prevalence of NRH was higher in both twins (16.19%) and their parents (15.09%). In the twins, LH and NRH were associated with parents' LH. Male sex and lower gestational age were associated with NRH, and LH was associated with not being breastfed. MH was related to neurodevelopmental delays and higher externalizing problems later in childhood. Other previously reported associations were not replicated, and no twin-specific characteristics were related to handedness. These results emphasize the importance of considering multiple definitions of handedness and indicate a small number of replicated associations across studies.

The Effects of Hand Preference on Measures of Psychological Well-Being in a Sample of Older Adults in the Kingdom of Saudi Arabia

BACKGROUND

Generally, being left-handed has been linked to poorer mental health and quality of life. However, given that few studies have investigated these links in Saudi Arabia and that the prevalence of mental illness in the general population is rising, it is important to explore whether left-handedness can be considered a risk factor in a sizable, general population.

AIM

To investigate whether left-handers experience psychological well-being or good quality of life.

METHODS

A cross-sectional study among adults in Saudi Arabia was conducted from March 6, 2022 to February 27, 2023.

RESULTS

The study included (N = 2862) respondents who met the inclusion criteria, with an average age of 28.95 years. Left-handed individuals made up 31.7%, whereas right-handed individuals made up 60.3%, and ambidextrous individuals made up 7.9% of the population. Using the Mental Health Quality of Life questionnaire (MHQoL-7D) scoring manual, the quality of life for both left-and right-handers was evaluated. Those who were right-handed had a higher quality of life than those who were left-handed. Multivariate Analysis of Variance (MANOVA) was conducted, and the findings showed that neither the left-handed nor the right-handed group significantly differed in their levels of poor quality of life or psychological well-being.

CONCLUSION

Using the left or the right hand had no effect on one's quality of life or degree of well-being. Further studies with a larger sample size are needed to examine this result in more detail.

Remote working during the COVID-19 pandemic: Computer-related musculoskeletal symptoms in university staff

BACKGROUND

The COVID-19 pandemic resulted in mandatory remote working for workers in many sectors, including education.

OBJECTIVE

This study aimed to investigate the physical characteristics of workspaces, computer use, and prevalence, associated factors, and reported impact of computer-related musculoskeletal symptoms (MSS) among university staff during the COVID-19 pandemic.

METHODS

A cross-sectional study of staff in a university in Ireland was conducted in March 2021. An anonymous online survey of computer use, work practices and 3-month prevalence and the reported impact of computer-related MSS (modified Nordic Musculoskeletal Questionnaire) was conducted. Data analysis involved descriptive statistics and relationships were tested using chi-squared analysis.

RESULTS

The analysis included 1045 responses. The majority (63%) worked solely from home, used a laptop more frequently than a desktop computer, and worked a greater number of hours. Almost half (48%) did not have a dedicated home workspace. More respondents reported their university workspace (72%) was more comfortable than their home workspace (51.2%) (p < 0.0001). Prevalence of computer-related MSS was 83% : neck (62%), shoulder (57%), lower back (47%). Laptop-related MSS was reported more frequently (82%) than desktop-related MSS (65%) (p < 0.05). Computer-related MSS was associated with workspace, equipment at home, laptop use, female gender, and righthandedness (p < 0.05). A reduction in non-work-related activities (35%), work activities (18%) and seeking medical attention (24%) was reported.

CONCLUSION

The prevalence of computer-related MSS was high and associated with remote working. Further studies that aim to mitigate the risks of computer-related MSS in those working remotely or in hybrid models are required.

Behavioral laterality is correlated with problem-solving performance in a songbird

Cerebral lateralization, which is often reflected in an individual's behavioral laterality (e.g., handedness and footedness), may bring animals certain benefits such as enhanced cognitive performance. Although the lateralization-cognition relationship has been widely studied in humans and other animals, current evidence supporting their relationship is ambiguous and warrants additional insights from more studies. Moreover, the lateralization-cognition relationship in non-human animals has been mostly studied in human-reared populations, and investigations of wild populations are particularly scarce. Here, we test the footedness of wild-caught male yellow-bellied tits (Pardaliparus venustulus) and investigate its association with their performance in learning to solve a toothpick-pulling problem and a drawer-opening problem. The tested birds showed an overall trend to gradually spent less time solving the problems, implying that they learned to solve the problems. Left- and right-footed individuals showed no significant differences in the latency to explore the experimental apparatuses and in the proportions that completed and did not complete the tasks. However, the left-footed individuals learned faster than the right-footed individuals in the drawer-opening experiment, indicating a potential cognitive advantage associated with left-footedness. These results contribute to the understanding of the behavioral differences between differently footed individuals and, in particular, the relationship between lateralization and cognitive ability in wild animals.

High intra-task and low inter-task correlations of motor skills in humans creates an individualized behavioural pattern

Our motor system allows us to generate an enormous breadth of voluntary actions, but it remains unclear whether and how much motor skill translates across tasks. For example, if an individual is good at gross motor control, are they also good at fine motor control? Previous research about the generalization across motor skills has been equivocal. Here, we compare human performance across five different motor skills. High correlation between task measures would suggest a certain level of underlying sensorimotor ability that dictates performance across all task types. Low correlation would suggest specificity in abilities across tasks. Performance on a reaching task, an object-hitting task, a bimanual coordination task, a rapid motion task and a target tracking task, was examined twice in a cohort of 25 healthy individuals. Across the cohort, we found relatively high correlations for different spatial and temporal parameters within a given task (16-53% of possible parameter pairs were significantly correlated, with significant r values ranging from 0.53 to 0.97) but relatively low correlations across different tasks (2.7-4.4% of possible parameter pairs were significantly correlated, with significant r values ranging from 0.53-0.71). We performed a cluster analysis across all individuals using 76 performance measures across all tasks for the two repeat testing sessions and demonstrated that repeat tests were commonly grouped together (16 of 25 pairs were grouped next to each other). These results highlight that individuals have different abilities across motor tasks, and that these patterns are consistent across time points.

Machine learning of large-scale multimodal brain imaging data reveals neural correlates of hand preference

Lateralization is a fundamental characteristic of many behaviors and the organization of the brain, and atypical lateralization has been suggested to be linked to various brain-related disorders such as autism and schizophrenia. Right-handedness is one of the most prominent markers of human behavioural lateralization, yet its neurobiological basis remains to be determined. Here, we present a large-scale analysis of handedness, as measured by self-reported direction of hand preference, and its variability related to brain structural and functional organization in the UK Biobank (N = 36,024). A multivariate machine learning approach with multi-modalities of brain imaging data was adopted, to reveal how well brain imaging features could predict individual's handedness (i.e., right-handedness vs. non-right-handedness) and further identify the top brain signatures that contributed to the prediction. Overall, the results showed a good prediction performance, with an area under the receiver operating characteristic curve (AUROC) score of up to 0.72, driven largely by resting-state functional measures. Virtual lesion analysis and large-scale decoding analysis suggested that the brain networks with the highest importance in the prediction showed functional relevance to hand movement and several higher-level cognitive functions including language, arithmetic, and social interaction. Genetic analyses of contributions of common DNA polymorphisms to the imaging-derived handedness prediction score showed a significant heritability (h²=7.55%, p <0.001) that was similar to and slightly higher than that for the behavioural measure itself (h²=6.74%, p <0.001). The genetic correlation between the two was high (r_g=0.71), suggesting that the imaging-derived score could be used as a surrogate in genetic studies where the behavioural measure is not available. This large-scale study using multimodal brain imaging and multivariate machine learning has shed new light on the neural correlates of human handedness.

Discovery of 42 genome-wide significant loci associated with dyslexia

Reading and writing are crucial life skills but roughly one in ten children are affected by dyslexia, which can persist into adulthood. Family studies of dyslexia suggest heritability up to 70%, yet few convincing genetic markers have been found. Here we performed a genome-wide association study of 51,800 adults self-reporting a dyslexia diagnosis and 1,087,070 controls and identified 42 independent genome-wide significant loci: 15 in genes linked to cognitive ability/educational attainment, and 27 new and potentially more specific to dyslexia. We validated 23 loci (13 new) in independent cohorts of Chinese and European ancestry. Genetic etiology of dyslexia was similar between sexes, and genetic covariance with many traits was found, including ambidexterity, but not neuroanatomical measures of language-related circuitry. Dyslexia polygenic scores explained up to 6% of variance in reading traits, and might in future contribute to earlier identification and remediation of dyslexia.

The influence of vestibular system and fetal presentation on handedness, cognitive and motor development: A comparison between cephalic and breech presentation

Genetics are undoubtedly implicated in the ontogenesis of laterality. Nonetheless, environmental factors, such as the intrauterine environment, may also play a role in the development of functional and behavioral lateralization. The aim of this study was to test the Left-Otolithic Dominance Theory (LODT; Previc, 1991) by investigating a hypothetical developmental pattern where it is assumed that a breech presentation, which is putatively associated with a dysfunctional and weakly lateralized vestibular system, can lead to weak handedness and atypical development associated with language and motor difficulties. We used the ALSPAC cohort of children from 7 to 10 years of age to conduct our investigation. Our results failed to show an association between the vestibular system and fetal presentation, nor any influence of the latter on hand preference, hand performance, or language and motor development. Bayesian statistical analyses supported these findings. Contrary to our LODT-derived hypotheses, this study offers evidence that fetal presentation does not influence the vestibular system's lateralization and seems to be a poor indicator for handedness. Nonetheless, we found that another non-genetic factor, prematurity, could lead to atypical development of handedness. This article is protected by copyright. All rights reserved.

Look beyond the Mirror: Laparoscopic Cholecystectomy in Situs Inversus Totalis—A Systematic Review and Meta-Analysis (and Report of New Technique)

Background: Laparoscopic cholecystectomy in situs inversus totalis (SIT) is a technically and physically demanding procedure for surgeons and there is still a lack of consensus regarding the best technical approach in such cases. We conducted a systematic review and meta-analysis to evaluate port placement, the dominant hand of the surgeon, preoperative imaging, morbidity, and mortality. Methods: We searched MEDLINE, SCOPUS, Web of Science, and the Cochrane Library for studies of patients with SIT that underwent laparoscopic cholecystectomy. Of 387 identified records, 101 met our inclusion criteria, all of them case reports or case series of maximum of 6 patients. Results: Out of the 121 patients included in the analysis, 94 were operated on using a “mirrored American” technique, 12 using the “Mirrored French”, 9 employed single-port techniques, and 6 described novel port placements. Even though most surgeries were conducted by a right-handed surgeon (93 cases), surgeries performed by the seven left-handed surgeons yielded shorter intervention times (p = 0.024). Preoperative imaging (CT, MRI, MRCP, ERCP) also correlated with a lower duration of surgery (p = 0.038. Length of stay was associated with the type of disease, but not with other studied endpoints. Morbidity was less than 1%, and conversion rates and mortality were nil. Conclusions: Cholecystectomy in SIT is a safe but challenging procedure and surgeons should prepare in advance for the unfamiliar aspects of completing such a task. While preoperative imaging and a left-handed surgeon are beneficial in terms of surgery length, when these are not available surgeons should focus on achieving the most comfortable setting based on their experience and tailor their approach to the patient at hand. Further studies are needed in order to properly describe and evaluate intraoperative findings as well as surgeon-dependent factors that could improve future recommendations.

Lateralized Changes in Language Associated Auditory and Somatosensory Cortices in Autism

Lateralized specialization of the two cerebral hemispheres is a fundamental structural hallmark of the human brain and underlies many cognitive functions and behavioral abilities. In typical developing individuals the influence of handedness on performance of various sensory modalities and the cortical processing has been well recognized. Increasing evidence suggests that several neurodevelopmental and psychiatric disorders such as bipolar disorder, schizophrenia, and autism spectrum disorders (ASD) are associated with abnormal patterns of cerebral lateralization. Individuals with ASD exhibit abnormal structural and functional lateralization of circuits subserving motor, auditory, somatosensory, visual face processing, and language-related functions. Furthermore, a high prevalence of atypical handedness has been reported in ASD individuals. While the hemispheric dominance is also related to functions other than handedness, there is a clear relationship between handedness and language-related cortical dominance. This minireview summarizes these recent findings on asymmetry in somatosensory and auditory cortical structures associated with language processing in ASD. I will also discuss the importance of cortical dominance and interhemispheric disruption of balance between excitatory and inhibitory synapses as pathophysiological mechanisms in ASD.

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.

The effects of sex and handedness on masturbation laterality and other lateralized motor behaviours

Masturbation is a common human behaviour. Compared to other unimanual behaviours it has unique properties, including increased sexual and emotional arousal, and privacy. Self-reported hand preference for masturbation was examined in 104 left-handed and 103 right-handed women, and 100 left-handed and 99 right-handed men. Handedness (modified Edinburgh Handedness Inventory, EHI), footedness, eyedness, and cheek kissing preferences were also measured. Seventy nine percent used their dominant hand (always/usually) for masturbation, but left-handers (71.5%) were less consistently lateralized to use their dominant hand than right-handers (86.5%). Hand preference for masturbation correlated more strongly with handedness (EHI), than with footedness, eyedness, or cheek preference. There was no difference in masturbation frequency between left- and right-handers, but men masturbated more frequently than women, and more women (75%) than men (33%) masturbated with sex aids. For kissing the preferred cheek of an emotionally close person from the viewer's perspective, left-handers showed a left-cheek preference, and right-handers a weaker right-cheek preference. The results suggest that hemispheric asymmetries in emotion do not influence hand preference for masturbation but may promote a leftward shift in cheek kissing. In all, masturbation is lateralized in a similar way to other manual motor behaviours in left-handed and right-handed men and women.

Assessment of morphological differences of the proximal tibia in healthy knees: analysis of the 3-dimensional mathematical model

Background

High tibial osteotomy and many orthopedic surgical procedures around the knee joint requires precise preoperative planning. In-depth knowledge of the tibial plateau morphology is necessary to limit intraoperative complications like lateral hinge fracture. No studies were exploring the differences in proximal tibia surface geometry, in regards to gender and laterality, using a mathematical model. The aim of our study was to assess morphological differences in healthy knees using a three-dimensional mathematical model.

Methods

Eighty-seven computed tomography examinations collected from 52 patients were selected for the study. The inclusion criteria were: age between 20 and 40 years, knee joint without visible deformities, no history of significant trauma to index knee, no history of systemic and chronic disorders. The average age of the included patients was 32.5±8.9 years old. For the calculation and comparisons, 45 right knee joints (18 females and 27 males) and 42 left knee joints (17 females and 25 males) were used.

Results

The male tibial plateau was much larger than the female one, for the right (P=0.001) and left knees (P=0.001). Male knees showed much bigger variability in two-dimensional tibial plateau dimensions especially for the left knees (P=0.001), and there was also a marked difference in variability between sides in males. Three-dimensional variability was significant for medial condyles for both genders. Male knees had a statistically bigger (P=0.04) tibial plateau surface area for all measured condyles.

Conclusions

The proximal tibial plateau showed in the designed mathematical models high variability in the two-dimensional and three-dimensional analysis. The males' knees presented great variability between sides and condyles. This finding must be considered during preoperative planning.

Large-Scale Phenomic and Genomic Analysis of Brain Asymmetrical Skew

The human cerebral hemispheres show a left-right asymmetrical torque pattern, which has been claimed to be absent in chimpanzees. The functional significance and developmental mechanisms are unknown. Here, we carried out the largest-ever analysis of global brain shape asymmetry in magnetic resonance imaging data. Three population datasets were used, UK Biobank (N = 39 678), Human Connectome Project (N = 1113), and BIL&GIN (N = 453). At the population level, there was an anterior and dorsal skew of the right hemisphere, relative to the left. Both skews were associated independently with handedness, and various regional gray and white matter metrics oppositely in the two hemispheres, as well as other variables related to cognitive functions, sociodemographic factors, and physical and mental health. The two skews showed single nucleotide polymorphisms-based heritabilities of 4-13%, but also substantial polygenicity in causal mixture model analysis, and no individually significant loci were found in genome-wide association studies for either skew. There was evidence for a significant genetic correlation between horizontal brain skew and autism, which requires future replication. These results provide the first large-scale description of population-average brain skews and their inter-individual variations, their replicable associations with handedness, and insights into biological and other factors which associate with human brain asymmetry.

Do you know your best side? Awareness of lateral posing asymmetries

People tend to show the left cheek to broadly express emotions while they tend to show the right cheek to hide emotions because emotions were expressed more on the left than on the right side of the face. The present study investigated the level of awareness on the left- and right-cheek poses using the method of structural knowledge attributions. When asked to broadly express emotions for a family portrait, right-handed participants were more likely to show the left cheek than the right. On the other hand, when asked to conceal emotions to show a calm and reassuring attitude as a scientist, they were more likely to show the right cheek. After the posing session, participants selected the conscious level of their knowledge about posing from five categories: Random, intuition, familiarity, recollection, and rules. Most participants rated their knowledge as unconscious (i.e., either as random, intuition, or familiarity). The choice of the conscious level did not differ across posing orientations and posing instructions. These results suggest that although people do not have an acute awareness of their lateral posing preference, they reliably show one side of their faces to express or hide emotions.

Exploring Co-creative Drawing Workflows

This article presents the outcomes from a mixed-methods study of drawing practitioners (e.g., professional illustrators, fine artists, and art students) that was conducted in Autumn 2018 as a preliminary investigation for the development of a physical human-AI co-creative drawing system. The aim of the study was to discover possible roles that technology could play in observing, modeling, and possibly assisting an artist with their drawing. The study had three components: a paper survey of artists' drawing practises, technology usage and attitudes, video recorded drawing exercises and a follow-up semi-structured interview which included a co-design discussion on how AI might contribute to their drawing workflow. Key themes identified from the interviews were (1) drawing with physical mediums is a traditional and primary way of creation; (2) artists' views on AI varied, where co-creative AI is preferable to didactic AI; and (3) artists have a critical and skeptical view on the automation of creative work with AI. Participants' input provided the basis for the design and technical specifications of a co-creative drawing prototype, for which details are presented in this article. In addition, lessons learned from conducting the user study are presented with a reflection on future studies with drawing practitioners.

Asymmetry of Muscle Mass Distribution and Grip Strength in Professional Handball Players

Handball is among the disciplines that impose a significant degree of asymmetry on the body movement. The aim of the study is to assess the influence of physical effort on the occurrence of asymmetry in body musculature and in isometric strength of handball players. The study examined 36 professional handball players. Players' height and body mass were measured as to calculate their body mass indexes (BMIs). Segmental bioelectrical impedance analysis (SBIA) was used to assess: the percentage of fat mass, total muscle mass (MM), musculature of the right and left side of the body, and body segments (trunk, upper and lower limbs). Moreover, grip strength was also measured. The assessment confirmed the existence of discrepancies in the right and left sides of players' bodies for the majority of the parameters. Cross-asymmetry and significant bilateral discrepancies in trunk musculature were also observed. Morphological asymmetry may impact performance in sports since it can cause unfavorable functional changes, which in turn increase the risk of injury and conditions caused by overexertion. Therefore, we believe it is important to emphasize the importance of individualized symmetrization during sports practice and consistent monitoring of the asymmetries occurring in different body parts; this should both improve one's sports results and minimize the risk of injury.

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.

Direct Reproduction and Sexual Orientation and Gender Diversity in Thailand

Human same-sex sexual attraction is considered to be an evolutionary paradox. This paradox rests on same-sex attracted individuals having lowered direct reproduction, indicating reduced direct fitness of genes that influence same-sex attraction. Yet, relatively few empirical studies have examined the relation between same-sex sexual attraction and direct reproduction. The present study examined direct reproduction (i.e., number of children produced) in a diverse Thai sample (N = 1623) of heterosexual men and women, gay and bisexual men, and lesbian and bisexual women, as well as unique Thai gender categories: sao praphet song (i.e., feminine androphilic third-gender males), toms (i.e., masculine gynephilic third-gender females), and dees (i.e., feminine females who are sexually attracted to toms). In males, heterosexual men were more likely to have produced children than other groups, especially as they aged, and none of the gay men or sao praphet song reported having children. In females, there was some degree of reproduction in each of the groups considered. On average, heterosexual and bisexual women had similar numbers of children, whereas heterosexual women had significantly more children than lesbian women, toms, and dees. Number of children was significantly positively associated with age among heterosexual women, bisexual women, toms, and dees. With age, the discrepancies in average number of children produced between heterosexual women and each of lesbian women and toms became significantly more pronounced. Discussion focuses on how these findings, in conjunction with those of prior studies, inform our understanding of evolutionary selection pressures related to human same-sex sexuality.

Left-Handedness Among Orthopaedic Surgeons and Trainees

Background:

The impact of left-handedness on orthopaedic surgeons and trainees has not been well described. We investigated the prevalence and perceived impact of left-handedness among orthopaedic surgeons and trainees.

Methods:

We distributed a survey regarding handedness to active members of the American Orthopaedic Association and the Council of Orthopaedic Residency Directors affiliates, including department chairs, program directors, and residency and fellowship program coordinators. Program coordinators were asked to distribute the survey to their current residents and fellows.

Results:

Of 510 survey respondents, 78 (15%) were identified as left hand dominant (LHD). Regarding scalpel/cautery use, 64% of LHD respondents reported using their left hand primarily and 10% reported using their right hand primarily; 26% of LHD respondents described themselves as ambidextrous in scalpel/cautery use, compared with 4.7% of right hand dominant (RHD) respondents (p < 0.001). Regarding suturing, 53% of LHD respondents reported using their left hand primarily and 38% reported using their right hand primarily; 9.0% of LHD respondents described themselves as ambidextrous when suturing, compared with 1.9% of RHD respondents (p = 0.012). Only 5.1% of LHD respondents reported having received laterality-specific psychomotor training, whereas 17% perceived a need for such training during residency; RHD respondents reported similar rates. Ambidexterity in scalpel/cautery use or suturing among LHD respondents was not associated with the perception that their left-handedness was advantageous. LHD attending surgeons were more likely than LHD trainees to perceive their handedness as advantageous (p = 0.007).

Conclusions:

Fifteen percent of orthopaedic surgeons and trainees who responded to our survey were LHD. LHD respondents reported significantly higher rates of ambidexterity in both scalpel/cautery use and suturing compared with RHD respondents. Ambidexterity was not associated with a self-perception that left-handedness was advantageous. LHD-attending surgeons were significantly more likely than LHD residents/fellows to perceive their left-handedness as advantageous. There may be benefits to pairing LHD residents with LHD faculty surgeons early in their training to provide mentorship and insight regarding performing surgical procedures left handed.

Level of Evidence:

Level IV.

Motor competence is not enough: Handedness does not facilitate visual anticipation of same-handed action outcome

Visual understanding of others performing an action depends on both an observer's visual and motor experience with that action. With regard to visual anticipation of lateralized action outcome in one-on-one confrontative situations, however, the particular role of motor experience is poorly understood. Here, we considered handedness to test the laterality-specific contribution of visual and motor experience to action outcome anticipation. In two experiments, 55 left- and 114 right-handed handball players predicted the outcome (Exp. 1: throw direction; Exp. 2: type of throw) of videos showing left- and right-handed penalty-throws viewed from a goalkeeper's perspective. Analyses reveal that left- and right-handed participants performed similarly and had more difficulties anticipating the outcome direction, but not type of throw, of left- compared to right-handed penalties. Thus, albeit left- and right-handers differ in their lateralized motor experience, this does not seem to be sufficient to facilitate visual anticipation of same-handed action outcome. Instead, findings lend further support to the specificity of perceptual learning and visual experience arising from both left- and right-handers' predominant exposure to more common right-handed movements.

Implicit Motives, Laterality, Sports Participation and Competition in Gymnasts

The implicit motivational needs for power, achievement, and affiliation are relevant for sports performance. Due to their hypothesized association with functions of the right hemisphere (McClelland, 1986), they may influence lateralized perceptual and motor processes. And due to their interactions with motive-specific incentives, they may influence performance conditional on the presence of suitable incentives. This preregistered study, conducted mostly online, examines motivational needs using a standard picture-story exercise (PSE) and their associations with indicators of perceptual and motor laterality and sports performance in gymnasts (N = 67). Further it explores how implicit motives interact with suitable motivational incentives in the prediction of sports performance. Results partly confirm a link between indicators of cerebral rightward laterality and implicit motives: the implicit affiliation and achievement motives are positively associated with an indicator of emotional-perceptional laterality (chimeric-faces task), but not with an indicator of motor laterality (turning bias). Moreover, the implicit achievement motive was positively correlated with training hours. The implicit affiliation motive was negatively associated with the highest attained competition level. The presence of achievement incentives (perceived control, failure) and affiliation incentives (training together or alone) did not interact with corresponding motives to predict sports performance.

Prevalence and heritability of handedness in a Hong Kong Chinese twin and singleton sample

BACKGROUND

Left-handedness prevalence has been consistently reported at around 10% with heritability estimates at around 25%. Higher left-handedness prevalence has been reported in males and in twins. Lower prevalence has been reported in Asia, but it remains unclear whether this is due to biological or cultural factors. Most studies are based on samples with European ethnicities and using the preferred hand for writing as key assessment. Here, we investigated handedness in a sample of Chinese school children in Hong Kong, including 426 singletons and 205 pairs of twins, using both the Edinburgh Handedness Inventory and Pegboard Task.

RESULTS

Based on a binary definition of writing hand, we found a higher prevalence of left-handedness (8%) than what was previously reported in Asian datasets. We found no evidence of increased left-handedness in twins, but our results were in line with previous findings showing that males have a higher tendency to be left-handed than females. Heritability was similar for both hand preference (21%) and laterality indexes (22%). However, these two handedness measures present only a moderate correlation (.42) and appear to be underpinned by different genetic factors.

CONCLUSION

In summary, we report new reference data for an ethnic group usually underrepresented in the literature. Our heritability analysis supports the idea that different measures will capture different components of handedness and, as a consequence, datasets assessed with heterogeneous criteria are not easily combined or compared.

A thousand studies for the price of one: Accelerating psychological science with Pushkin

Half of the world's population has internet access. In principle, researchers are no longer limited to subjects they can recruit into the laboratory. Any study that can be run on a computer or mobile device can be run with nearly any demographic anywhere in the world, and in large numbers. This has allowed scientists to effectively run hundreds of experiments at once. Despite their transformative power, such studies remain rare for practical reasons: the need for sophisticated software, the difficulty of recruiting so many subjects, and a lack of research paradigms that make effective use of their large amounts of data, due to such realities as that they require sophisticated software in order to run effectively. We present Pushkin: an open-source platform for designing and conducting massive experiments over the internet. Pushkin allows for a wide range of behavioral paradigms, through integration with the intuitive and flexible jsPsych experiment engine. It also addresses the basic technical challenges associated with massive, worldwide studies, including auto-scaling, extensibility, machine-assisted experimental design, multisession studies, and data security.

Baseline cortisol levels and social behavior differ as a function of handedness in marmosets (Callithrix jacchus)

Population hand preferences are rare in nonhuman primates, but individual hand preferences are consistent over a lifetime and considered to reflect an individual's preference to use a particular hemisphere when engaged in a specific task. Previous findings in marmosets have indicated that left-handed individuals tend to be more fearful than their right-handed counterparts. Based on these findings, we tested the hypotheses that left-handed marmosets are (a) more reactive to a social stressor and (b) are slower than right-handed marmosets in acquiring a reversal learning task. We examined the hand preference of 27 male and female marmosets (ages of 4-7 years old) previously tested in a social separation task and a reversal learning task. Hand preference was determined via a simple reaching task. In the social separation task, monkeys were separated from their partner and the colony for a single 7-hr session. Urinary cortisol levels and behavior were assessed at baseline, during the separation and 24 hr postseparation. Hand preferences were equally distributed between left (n = 10), right-handed (n = 10), and ambidextrous (n = 7) individuals. The separation phase was associated with an increase in cortisol levels and behavioral changes that were similar across handedness groups. However, cortisol levels at baseline were positively correlated with right-handedness, and this relationship was stronger in females than in males. In addition, the occurrence of social behaviors (pre- and postseparation) was positively correlated with right-handedness in both sexes. Baseline cortisol levels did not correlate significantly with social behavior. Acquisition of the reversals was poorer in females than males but did not differ as a function of handedness. We conclude that (a) both stress reactivity and cognitive flexibility are similar across handedness groups and (b) left-handers exhibit less social behavior and have lower basal cortisol levels than ambidextrous and right-handed subjects. The underlying causes for these differences remain to be established.

A sinister subject: Quantifying handedness-based recruitment biases in current neuroimaging research

Approximately ten per cent of humans are left-handed or ambidextrous (adextral). It has been suggested that, despite their sizable representation at the whole-population level, this demographic is largely avoided by researchers within the neuroimaging community. To date, however, no formal effort has been made to quantify the extent to which adextrals are excluded from neuroimaging-based research. Here, we aimed to address this question in a review of over 1,000 recent articles published in high-impact, peer-reviewed, neuroimaging-focused journals. Specifically, we sought to ascertain whether, and the extent to which adextrals are underrepresented in neuroimaging study samples, and to delineate potential trends in this bias. Handedness data were available for over 30,000 research subjects; only around 3%-4% of these individuals were adextral-considerably less than the 10% benchmark one would expect if neuroimaging samples were truly representative of the general population. This observation was generally consistent across different areas of research, but was modulated by the demographic characteristics of neuroimaging participants. The epistemological and ethical implications of these findings are discussed.

Avocado-related knife injuries: Describing an epidemic of hand injury

INTRODUCTION

Recent media reports have described knife injuries sustained while preparing avocados; however, this rise has not been reported in the literature. The purpose of this study is to describe, quantify, and trend emergency department (ED) encounters associated with avocado-related knife injuries.

METHODS

The National Electronic Injury Surveillance System (NEISS) was queried for avocado-related knife injuries from 1998 to 2017. Patient demographic and injury data was collected and analyzed to describe trends in incidence, patient demographics, and injury patterns associated with an ED encounter for an avocado-related knife injury.

RESULTS

There were an estimated 50,413 (95% Confidence Interval: 46,333-54,492) avocado-related knife injuries from 1998 to 2017. The incidence of avocado-related knife injuries increased over this time period (1998-2002 = 3143; 2013-2017 = 27,059). This increase correlated closely with a rise in avocado consumption in the U.S. (Pearson's Correlation: 0.934, p < 0.001) Women comprised 80.1% of injuries. The most common demographic injured were 23 to 39-year old females (32.7%), while the least common was males under the age of 17 (0.9%). Most ED presentations occurred on Saturdays (15.9%) or Sundays (19.9%) and the majority occurred during the months of April through July (45.6%). Injuries were much more common on the left (and likely non-dominant) hand.

CONCLUSION

Avocado-related knife injuries are a preventable cause of hand injury. The incidence has risen significantly in recent years, possibly due to an increased consumption of avocados in the United States. Education on safe avocado preparation techniques and public safety initiatives, such as warning labels, could help prevent serious injuries in the future.

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.

Hand and foot preference in two cultures

Adult participants from India and France were requested to respond to hand and foot preference questionnaires. The items of the questionnaires assessed the choice of the preferred hand and foot on a scale that ranged from extreme left preference through no preference to extreme right preference. Results showed that both groups were more right lateralized for hand actions, whereas foot preferences were less right lateralized and spread across extreme right preference to no preference on the laterality index continuum for men and women. As compared to requiring large numbers for consistency in hand preferences across geographical regions, trends in the lateralization of hand and foot preferences may be consistently obtained with smaller samples. The study reveals the existing difference in lateral preferences between the upper and lower limbs that is sustained regardless of culture or geographical location and indicates the need for further investigation to know why the lower limbs are less lateralized than the upper limbs.

A large-scale population study of early life factors influencing left-handedness

Hand preference is a conspicuous variation in human behaviour, with a worldwide proportion of around 90% of people preferring to use the right hand for many tasks, and 10% the left hand. We used the large cohort of the UK biobank (~500,000 participants) to study possible relations between early life factors and adult hand preference. The probability of being left-handed was affected by the year and location of birth, likely due to cultural effects. In addition, hand preference was affected by birthweight, being part of a multiple birth, season of birth, breastfeeding, and sex, with each effect remaining significant after accounting for all others. Analysis of genome-wide genotype data showed that left-handedness was very weakly heritable, but shared no genetic basis with birthweight. Although on average left-handers and right-handers differed for a number of early life factors, all together these factors had only a minimal predictive value for individual hand preference.

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

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

Subtle left-right asymmetry of gene expression profiles in embryonic and foetal human brains

Left-right laterality is an important aspect of human -and in fact all vertebrate- brain organization for which the genetic basis is poorly understood. Using RNA sequencing data we contrasted gene expression in left- and right-sided samples from several structures of the anterior central nervous systems of post mortem human embryos and foetuses. While few individual genes stood out as significantly lateralized, most structures showed evidence of laterality of their overall transcriptomic profiles. These left-right differences showed overlap with age-dependent changes in expression, indicating lateralized maturation rates, but not consistently in left-right orientation over all structures. Brain asymmetry may therefore originate in multiple locations, or if there is a single origin, it is earlier than 5 weeks post conception, with structure-specific lateralized processes already underway by this age. This pattern is broadly consistent with the weak correlations reported between various aspects of adult brain laterality, such as language dominance and handedness.

The association of diameter and depth of internal jugular and subclavian veins with hand dominancy

Background

The central veins’ catheterization, required in critically ill patients, is more successful in larger veins. Some researchers hypothesized that hand preference might be associated with larger ipsi/contra central veins.

Objective

To determine the diameter and depth of internal jugular and subclavian veins on both sides and its association with left- or right-handedness.

Methods

This cross-sectional study, was conducted on patients referring for elective breast or thyroid check-up to Shahid Faghihi Hospital ultrasound unit, Shiraz, Iran, from September 2014 to May 2015. Inclusion criteria consisted of adult normotensive patients with American Society of Anesthesiology (ASA) class I without underlying diseases. The patients’ demographics were recorded and the diameter and depth of the internal jugular and subclavian veins were measured by ultrasound. The results of measurements were compared between patients’ hand preference by SPSS version 19, using paired-samples t-test and independent-samples t-test.

Results

Of 65 patients, 86% were women and 19 were left-handed (29%) with the only significant difference between the right and left subclavian diameter in right-handed individuals (p=0.007) and no significant difference between the left and right internal jugular vein diameter and depth and subclavian vein depth between the left- and right-handed patients. The subclavian diameter of the right and left side was also not different in left-handed patients.

Conclusion

The right or left central veins are not superior to each other with respect to diameter and depth in right- or left-handed patients.

The androgen model of suicide completion

Suicide is a devastating public health issue that imposes severe psychological, social, and economic burdens not only for the individuals but also for their relatives, friends, clinicians, and the general public. Among the different suicidal behaviors, suicide completion is the worst and the most relevant outcome. The knowledge of biological etiopathological mechanisms involved in suicide completion is limited. Hitherto, no objective markers, either alone or in combination, can reliably predict who will complete a suicide. However, such parameters are strongly needed to establish and optimize prediction and prevention. We introduce here a novel ideation-to-completion framework in suicide research and discuss the problems of studies aiming at identifying and validating clinically useful markers. The male gender is a specific risk factor for suicide, which suggests that androgen effects are implicated in the transition from suicidal ideation to suicide completion. We present multiple lines of direct and indirect evidence showing that both an increased prenatal androgen load (with subsequent permanent neuroadaptations) and increased adult androgen activity are involved in suicide completion. We also review data arguing that modifiable maternal behavioral traits during pregnancy contribute to the offspring's prenatal androgen load and increase the risk for suicide completion later in life. We conclude that in utero androgen exposure and adult androgen levels facilitate suicide completion in an synergistic manner. The androgen model of suicide completion provides the basis for the development of novel predictive and preventive strategies in the future.