Lefties take note. A new Wall Street Journal report referencing several scientific studies connects left-hand dominance with neural disorders like ADHD and schizophrenia. But don't be too concerned just yet. Here, a few of the more "interesting" findings:
A link with schizophrenia?
Left-handedness "appears" to carry with it a greater risk for "a number of psychiatric and developmental disorders," says Shirley S. Wang at the Wall Street Journal. While lefties constitute just 10 percent of the overall population, a disproportionate 20 percent of people with schizophrenia are left-hand dominant, though the exact reasons remain unclear.
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And what about ADHD?
A 2008 Swedish study found that "left- or mixed- handedness in children" was linked to a "greater risk of difficulty with language as well as ADHD symptoms." Caveat: A separate 2010 study that analyzed 8,000 Finnish children concluded that "mixed-handedness rather than left-handedness was linked to ADHD symptoms."
What's causing the brain disorders?
The connection between handedness and neural function may have something to do with how a person is wired. Thanks to a concept called "brain lateralization," a person's brain typically has a dominant hemisphere, says Wang. Each hemisphere "performs primarily separate, specialized functions." Language processing, for instance, mainly takes place in the left hemisphere, which is typically dominant in right-handers. Recent studies suggest that "30 percent of lefties appear to exhibit a right-dominant or distributed pattern" in the brain, a cross-wiring which may make them "more prone to impaired learning or functioning, and at greater risk for brain disorders."
What determines which hemisphere becomes dominant?
Developmental issues in the womb are likely a factor. While "there is a 25 percent chance that genetics will play a part in defining a person's handedness," says Amy Windsor at Babble, several studies point to another determining factor: Developmental stress. "Older mothers and low birth weights are also more likely to produce left-handed children," notes Windsor. For example, in a Danish study, women who experienced "multiple traumas" while in their third trimester were three times as likely to produce mixed-handed children.
Should I be worried if my child is left-handed?
"This is interesting, but I wouldn't be too concerned," says Eric Berger at the Houston Chronicle. While the evidence suggests that left-handedness may be linked to learning disorders, there's lots of anecdotal evidence suggesting left-handedness is "a precursor to greatness" — six of the last 12 U.S. presidents, including Barack Obama and George H.W. Bush, have been left handed. And then there's "the salary a starting left-handed pitcher can claim in the major leagues."
Sources: Babble, Houston Chronicle, Wall Street Journal
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