The mixed bag of mixed handedness

I use my left hand for almost everything: writing, eating, and (if I were athletic) throwing—I am strongly left-handed. But some people—who are referred to as mixed-handed—don’t strongly favor one hand; they may use one hand for writing, another for throwing, and so on.

As reported this month in Scientific American, a study of 8,000 Finnish children determined that those without a dominant hand were more likely to have attention and language difficulties than children with left- or right-hand dominance. This indicates that when one hemisphere of the brain is not dominant, the two hemispheres may work together differently. Language is generally controlled by the left hemisphere, and attention the right; mixed-handed children with these difficulties might be getting too many signals from the right hemisphere and not enough from the left.

Alina Rodriguez of Uppsala University, the study’s lead researcher, is quick to point out that mixed-handedness is just one risk factor for a language or attention problem. In an earlier study, she suggested that mixed-handedness—and learning difficulties—can be caused in part by prenatal stress.

But mixed-handedness may also have benefits. Stephen Christman of the University of Toledo in Ohio has found that mixed-handed people tend to have earlier first memories than strongly right-handed people. The corpus collosum—the bundle of nerve fibers linking the brain’s hemispheres—tends to be larger in mixed-handed people. He posits that this leads to better memory recall, as episodic memory is encoded in the left hemisphere and retrieved in the right.

Cristman has also authored a study finding that mixed-handers are more gullible and more easily persuaded than people with dominant hands.

But fear not, mixed-handed people: there is a Facebook group just for you where you can discuss all the joys and difficulties of non-dominance.

— Johanna Goldberg

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