A sweeping new meta-analysis has revealed that individuals with mental or neurodevelopmental disorders are about 1.5 times more likely to exhibit non-right-handedness — meaning left-handedness or mixed-handedness — than the general population, sharpening the focus on how biological factors may intersect with mental health. Published in the prestigious journal Psychological Bulletin, the study synthesizes an unprecedented dataset drawn from over 202,000 people and provides fresh insights into the subtle ways brain development may be linked to mental health risk (psypost.org).
For Thais, most of whom are right-handed in line with global averages, this research highlights the curious overlap between brain lateralization, as reflected in handedness, and conditions such as schizophrenia, autism spectrum disorder, and intellectual disability. Understanding this link could eventually help destigmatize non-right-handedness and inform both education and mental health policy, especially as Thailand ramps up efforts to address mental health challenges facing its youth.
Handedness, or which hand a person prefers for tasks like writing or eating, is determined by a mix of genetic and environmental factors. It emerges early, even before birth, and has long been recognized as a proxy for the brain’s asymmetric development, especially in regions connected to language and motor functions (Wikipedia – Handedness). Previous research has suggested that disruptions in typical brain asymmetry might underlie both some unconventional hand use and elevated risk for developmental or psychiatric disorders, but until now the data had not been consolidated on a broad scale.
The latest synthesis was led by Dr. Julian Packheiser and colleagues, who undertook a “second-order meta-analysis.” In plain language, this means they combined results across 10 previous meta-analyses—each itself a review of many individual studies—then updated the evidence by including 33 newly published datasets. All told, their work spanned 402 datasets, compiling findings from over 202,000 participants around the world. Their study not only included information on hand dominance but closely tracked age, sex, clinical diagnosis, and even how handedness was measured in each research group.
Key findings are striking: across the mental health and neurodevelopmental conditions studied, people diagnosed with these disorders were about 50% more likely to be left-handed or mixed-handed compared to those with no such diagnoses. Mixed-handedness, where a person does not consistently prefer one hand over the other, showed the strongest association. The link was especially strong for schizophrenia, autism spectrum disorder, and intellectual disability, all of which had notably higher proportions of non-right-handed individuals. By comparison, more common conditions like depression and difficulties with math learning (dyscalculia) showed no significant differences relative to healthy peers.
Disorders rooted in neurodevelopment, such as attention-deficit hyperactivity disorder (ADHD), autism, dyslexia, intellectual disability, and childhood-onset stuttering, had the highest rates of non-right-handedness. This supports the idea that variations in early brain development—especially those impacting regions important for language—may underlie both unusual hand preferences and greater vulnerability to certain mental health issues.
The study’s authors also found that conditions linked to language difficulties, such as dyslexia and autism, had particularly strong associations with non-right-handedness. This fits with the well-established observation that the left side of the brain, which controls the right hand, is typically dominant for language. “Our findings support the hypothesis that atypical patterns of brain lateralization, which often manifest as non-right-handedness, could reflect deeper differences in neurodevelopment connected to both language and mental health risk,” explained a lead researcher from the study (psypost.org).
What significance might these findings hold for Thailand? In a society where left-handedness is sometimes discouraged in childhood—reflecting both practical barriers (for example, the layout of school desks or cultural traditions) and lingering social perceptions—this research could help normalize differences in handedness. Thai educators and mental health professionals may benefit from using information about handedness as one of several early indicators pointing to a need for developmental support. For instance, school counselors might be better equipped to address the diverse educational needs of children who display both atypical hand preference and early signs of learning or communication challenges.
Historically, Thailand has mirrored global patterns in the social construction of handedness, with strong stigmas around left-handedness—at times even encouraging children to switch hands. Yet this new research suggests that instead of pushing conformity, early recognition of non-right-handedness might offer a window into a child’s neurodevelopment and help guide more personalized support, especially for those at risk of neurodevelopmental or psychiatric conditions (Wikipedia – Left-handedness).
This study does not suggest that left-handedness or mixed-handedness causes mental health disorders, or vice versa. Rather, both may spring from common neurodevelopmental roots, likely set in motion early in life, which subtly alter the balance of brain function between hemispheres. Experts caution against using these findings to label or stigmatize left-handed individuals. Instead, the research illuminates the complexity of brain development and may help destigmatize difference in Thai society.
The findings could pave the way for more sensitive screenings and support in Thai schools, where early recognition of non-right-handedness might become part of a set of markers to help spot students who could benefit from further evaluation or support for learning differences. Likewise, raising public awareness that variations in handedness are a normal part of brain diversity might reduce stigma for both non-right-handed individuals and those living with neurodevelopmental conditions.
As mental health becomes an increasingly visible concern for Thailand’s youth—especially following the stresses of the COVID-19 pandemic and rising rates of reported learning difficulties—studies like this provide scientific grounding for efforts to make Thai classrooms, workplaces, and health systems more inclusive of brain-based diversity. Future Thai research may explore whether environmental responses, such as forcing left-handed children to use their right hand, could add stress or inadvertently affect brain development.
The authors note that a key limitation of the study was that they largely relied on binary definitions of handedness—right, left, or mixed—rather than capturing the full spectrum of hand preference. Future research could benefit from continuous measures, offering an even more nuanced view.
In light of these findings, practical recommendations for Thai parents, teachers, and policymakers include embracing a more flexible attitude toward handedness, promoting acceptance of brain diversity, and supporting early mental health screenings that include questions about developmental markers such as handedness. Most importantly, left-handed students should not be forced to conform; instead, their individual developmental needs, both neurotypical and atypical, deserve recognition. By fostering a climate of acceptance, Thailand can ensure that all children—regardless of which hand they use—have the best opportunity for growth and inclusion.
Further information and resources on handedness and mental health can be found via the Department of Mental Health Thailand and international research platforms such as PubMed.