Mixed-handedness tied to learning problems, ADHD

NEW YORK (Reuters Health) - Children who don't show a hand preference are more likely than their righty or lefty peers to perform poorly in school, a new study in the journal Pediatrics shows.

And these ambidextrous kids also show more signs of psychiatric disturbance and more symptoms of attention-deficit hyperactivity disorder (ADHD) at 8 and 16 years of age, Dr. Alina Rodriguez of Uppsala University in Sweden and University College London and her colleagues found.

Non-right-handedness has long been linked to behavior and learning problems, Rodriguez told Reuters Health. New research increasingly indicates that it's mixed-handedness, not left-handedness, that is responsible for the association, she added.

Rodriguez and her team recently showed that mixed-handed 5-year-olds had more language problems and ADHD symptoms than children who preferred using their right or left hand. In the current study, they looked at data reported by the parents and teachers of 7,871 Finnish children when the children were 7 or 8 years old and again when they were 16 years old.

Just 1 percent of the group were mixed-handed, which is similar to the prevalence seen in studies of adults; 9 percent were left-handed, and the rest were right handed.

At age 8, the mixed-handed children were more than twice as likely as their classmates to have poorer overall speaking ability and to perform poorly at school.

Mixed-handedness also emerged as a strong predictor of later behavior problems, the researchers found. For example, children who had no reading or writing problems at age 8 were nearly three times as likely to perform poorly in school at 16 if they were mixed-handed.

Kids who had behavior problems as 8-year-olds and were mixed-handed were 14 times as likely to have behavior problems at 16 compared to those who were well-behaved at 8 and were either right- or left-handed. These children were also nearly 17 times as likely to have overall behavioral scores suggesting psychiatric disturbance.

The two sides or hemispheres of the brain are normally quite different from one another in both structure and function, Rodriguez and her team note, while abnormally symmetrical brain hemispheres have been tied to brain and behavior problems.

It's likely that this kind of "atypical lateralization" is related to both mixed-handedness and behavior and learning problems, according to Rodriguez.

The fact that many renowned geniuses were mixed-handed -- like Albert Einstein and Leonardo da Vinci -- suggests that lack of hand preference may offer some advantages in brain development, she added.

"If a child is mixed handed I wouldn't worry if there are no other problems whatsoever," Rodriguez said. But if there are "red flags" like ADHD in the family or behavioral and learning problems, "I think it's worth having extra evaluation for the child."

SOURCE: Pediatrics, February 2010.