Researchers at the University of Melbourne in Australia tested whether left-handed children have more difficulty than righties on a variety of skills. They measured physical health, mental health, and cognitive development. These researchers, led by David W. Johnston, found no correlation between left-handedness and mental or physical health, but did find a strong connection between cognitive development and handedness. Lefties scored lower than righties on tests of memory, vocabulary, mathematics and comprehension. Boys seemed more likely than girls to show a left-handedness disadvantage. Like the Kentucky scientists, these Australian researchers also concluded that handedness is related to differences in brain functioning.
Handedness Affects Mood Disorders As Well?
Jadon Webb and his fellow scientists, who found a high correlation between left-handedness and psychosis, found that patients with mood disorders, such as depression or bipolar disorder, were not more likely to be lefties. This is consistent with the earlier findings of researchers, who have presented conflicting data about rates about non-right-handedness in people with bipolar disorder.
However, research led by Cecilia Nowakowska, MD, did find that bipolar disorder is 50% more likely to appear in non-righties than in the general population. Despite her findings, Dr. Nowakowska maintains that further investigations are needed to assess whether bipolar disorder, hemispheric asymmetry, and non-right handedness are correlated.
What’s in it for the Lefties?
Writing with one’s left hand is not a sure-fire sign of psychosis looming in one’s future. The constellation of symptoms of Schizophrenia and Schizoaffective Disorder, such as hallucinations, delusions and paranoid beliefs, correlates with left-handedness, but left-handedness does not directly lead to psychosis! According to Dr. Webb, this finding is simply a biomarker which can help doctors identify mental disorders earlier. One day, it might even help doctors to effectively customize treatment for psychosis to each individual patient.
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Johnston, David W, et. al. Handedness, health and cognitive development: evidence from children in the NLSY. (2010). IZA Discussion Papers, No. 4774. Accessed November 10, 2013.
Knecht, S., et.al. Handedness and Hemispheric Language Dominance in Healthy Humans. (2000). Brain. 123 (12): 2512-2518.
Lyle, KB., et. al. Is Handedness Related to Anxiety? New Answers to an Old Question. (2013). Laterality. 18(5):520-35. Accessed November 10, 2013.
Nowakowska, C. , et. al. Increased Rate of Non-Right Handedness in Patients with Bipolar Disorder. (2008). Journal of Clinical Psychiatry. 69(5): 866-867.
Webb, Jadon R., et. al. Left-Handedness Among a Community Sample of Psychiatric Outpatients Suffering From Mood and Psychotic Disorders. (2013). Sage Open. doi: 10.1177. Accessed November 10, 2013.
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