The study looked at nearly 8,000 children, 87 of whom were mixed-handed, and found that mixed-handed seven and eight-year old children were twice as likely as their right-handed peers to have difficulties with language and to perform poorly in school. Using questionnaires, the researchers assessed the children when they reached seven to eight years of age and again at 15 to 16 years of age.
When they reached 15 or 16, mixed-handed adolescents were also at twice the risk of having symptoms of attention deficit/hyperactivity disorder (ADHD). They were also likely to have more severe symptoms of ADHD than their right-handed counterparts. It is estimated that ADHD affects between three to nine percent of school-aged children and young people.
The adolescents also reported having greater difficulties with language than those who were left- or right-handed. This is in line with earlier studies that have linked mixed-handedness with dyslexia.
Handedness is linked to the hemispheres in the brain. Previous research has shown that where a person's natural preference is for using their right hand, the left hemisphere of their brain is more dominant. Some researchers have suggested that mixed-handedness indicates that the pattern of dominance is not that which is typically seen in most people, that means it is less clear that one hemisphere is dominant over the other. One study has suggested that ADHD is linked to having a weaker function in the right hemisphere of the brain, which could help explain why some of the mixed-handed students in today's study had symptoms of ADHD.
Alina Rodriguez, the lead researcher on the study, said: "Mixed-handedness is intriguing – we do not know why some people prefer to make use of both hands when most people use only one. Our study is interesting because it suggests that some children who are mixed handed experience greater difficulties in school than their left- and right-handed friends. We think that there are differences in the brain that might explain these difficulties, but there needs to be more research.”
MEDICA.de; Source: Imperial College London