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A recent study from Germany suggests a notable link between left-handedness and certain mental disorders. Conducted by researchers at Ruhr University Bochum and the Medical School Hamburg, the study analyzed data from over 200,000 individuals. It found that people with disorders like schizophrenia, autism, and intellectual disabilities are more likely to be left-handed compared to the general population. The findings, published in the Psychological Bulletin, indicate that while about 10% of people worldwide are left-handed, autism cases are 3.5 times more likely to exhibit non-right-handedness.
The researchers combined data from ten previous meta-analyses, representing 402 datasets, to identify patterns across different diagnoses. They found that mixed-handedness, where individuals use different hands for various tasks, showed even higher rates in clinical populations than left-handedness alone. According to Dr. Julian Packheiser, "Language, like handedness, has a very one-sided location in the brain, so it stands to reason that the development of both and their disorders could be linked."
The study highlights that hand preferences begin forming early, with prenatal thumb sucking at ten weeks gestation being a strong predictor of hand preference later in life. Interestingly, not all psychiatric conditions showed elevated left-handedness rates. Disorders like depression and dyscalculia showed no significant differences in handedness compared to control groups.
While the findings provide insight into brain development, the researchers caution against using handedness as a diagnostic tool. Many left-handed individuals never develop mental health conditions, and many people with these conditions are right-handed. This research offers a window into how our brains develop and organize themselves, suggesting that disruptions in these processes may affect both handedness and mental health.