Study Links Left-Handedness to Increased Risk of Certain Neurological Disorders

Recent research suggests that left-handed individuals may face a higher risk of developing specific neurological disorders. This new study, published in the journal Psychological Bulletin, explores the correlation between handedness and various psychiatric conditions, although researchers also note potential limitations in their findings.

Approximately 10% of the global population is left-handed. However, the study reveals that individuals diagnosed with autism are 3.5 times more likely to exhibit left-handed traits, according to a comprehensive analysis conducted by an international team involving over 200,000 participants.

Link Between Handedness and Mental Health

The research indicates that not only left-handedness but also mixed-handedness is more frequently observed among those with diagnoses like schizophrenia, autism, and intellectual disability. Mixed-handedness is characterized by individuals using their left hand for some tasks while employing their right hand for others, distinguishing it from true ambidexterity, where both hands are used equally.

Dr. Julian Packheiser, lead author and researcher at the Institute of Cognitive Neuroscience at Ruhr University Bochum, affirms that the significant takeaway from this study is that deviations from the typical right-handedness may associate particularly with psychiatric and psychological conditions affecting the language system, such as dyslexia or schizophrenia.

However, the study does not conclude that all neurological conditions have a demonstrated link to an individual’s dominant hand. For instance, disorders like depression and dyscalculia, a specific learning disability in math, did not show any significant differences in hand preference when compared to control groups.

Atypical Handedness and Long-Term Effects

Moreover, researchers found a possible association between atypical handedness and long-term linguistic challenges like stuttering and dyslexia. Dr. Earnest Lee Murray, a neurologist with West Tennessee Medical Group, who was not part of the study, elaborates that typical brain function establishes a dominant side where speech and language processing usually occurs.

In individuals who are left-handed or ambidextrous, language functions can be distributed across both brain hemispheres, leading to diverse neurodevelopmental patterns. This understanding may explain further why left-handedness correlates with certain neurological disorders.

Investigating Clinical Populations

The research team also focused on clinical populations diagnosed with specific health conditions, comparing them to control groups. The hypothesis posited that both left- and mixed-handedness might relate to disorders whose symptoms primarily involve language. Given that both language and handedness have identifiable, one-sided brain locations, the researchers suggest potential overlaps in their developmental pathways.

As the study progressed, it became evident that the emergence of a disorder’s symptoms earlier in life correlated with an increased incidence of left- and mixed-handedness among participants.

The study’s authors believe that since hand dominance tends to establish early in life, typically before birth, the traits might indicate underlying neurodevelopmental distinctions. Thumb-sucking behaviors observed in the womb, particularly around 10 weeks of gestation, could play a crucial role in determining future hand preference.

Implications for Understanding Brain Organization

Understanding these connections could lead to advances in neurorehabilitation techniques for patients suffering from conditions linked to one side of the brain, such as strokes or traumatic brain injuries, Dr. Murray notes. His insights underline the importance of this research in unraveling the complexities of brain organization and its developmental trajectory.

Despite the intriguing findings, experts urge caution. Jonathan Alpert, a Manhattan-based psychotherapist and author, acknowledges the study’s interesting implications but highlights its limitations. He stresses that correlation does not imply causation and that being left-handed does not inherently mean an individual will develop autism or schizophrenia.

Alpert emphasizes that handedness is just one variable among many that could influence neurological characteristics. He advocates for more research to thoroughly investigate the potential relationships between handedness and mental health outcomes.

Understanding Study Limitations

Dr. Packheiser concurs, stating that the current findings should be interpreted purely as correlational. There is no causal evidence available that suggests the development of psychiatric disorders linked to language or neurodevelopmental issues causes a change in handedness or vice versa.

Consequently, parents should not be alarmed if their child displays a preference for their left hand. Understanding the rise in mental disorders across populations, however, is crucial for fostering a deeper comprehension of these complex issues.

Overall, this study opens the door for further exploration into the associations between handedness and neurological health, offering valuable insights that could pave the way for future research and improved clinical practices.