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A switch in handedness changes the brain

July 17, 2007 By Kerri Smith This article courtesy of Nature News.

Forcing lefties to be righties results in more brain activity.

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'Southpaw', 'goofy', or just plain 'lefty' are some of the many names that left-handers have been called. In certain societies, the aversion can go so far that some left-handers are forced to write with their right hand, regardless of their natural tendencies.

Now, a study of such 'converted' left-handers has found that the way their brains are organized, and how hard particular regions work, changes as a result of this switch.

Some areas of the brain continue to look like those of a practising lefty, whereas other areas switch to the patterns of a righty, the research reveals. "The question now is, 'do converts suffer because of this extra attention that they exert?'," says Stefan Klöppel of University College London, who led the work. The answer to that is as yet unknown.

Mirror image

The hand used to write with is generally controlled by the opposite side of the brain — in right-handed people, movement-related areas on the left side of the brain are more active when they move the fingers of their right hand. But converting from being left-handed to right-handed doesn't simply move brain activity to the other half of the brain, Klöppel and his colleagues found.

The team tested right-handers, left-handers and converts (from left- to right-handedness) on a simple task, in which they pressed a button with one or the other hand in response to seeing particular symbols. Throughout the task their brain activity was monitored with a magnetic resonance imaging (MRI) scan.

One movement-related area of the brain was, as expected, most active in the right hemisphere for left-handers, and in the left hemisphere for right-handers — including natural lefties who converted to using their right hand. But activity in this region was greater in the converts, the researchers found. The more fully converted to right-handed writing that a lefty had become, the greater this activity.

But a second set of brain regions involved in planning movement stubbornly refuse to switch, and continue to act like those of left-handers in people who have switched to right-handedness. These stubborn regions were also more active in converts than in those who stuck with left-handedness. "They still look like left handers, but even more emphasised," says Klöppel, whose results are published in the Journal of Neuroscience1.

Hard workers?

There might be greater activity in their brains, but it would be a jump too far to conclude that converted lefties are adversely affected, says Clare Porac, a psychologist at Pennsylvania State University. "I wouldn't interpret that their brains are working harder," she says.

A lot of switched left-handers are adept at using both hands for many manual skills, she notes. This fits in well with the fact that there was activity on both sides of the brain in converted lefties.

Although it's less common in the United States and Europe to force people to become right-handed writers, the practice still goes on elsewhere. Porac has teamed up with Brazil-based researcher Lee Martin of the Federal University of Pará in Belém to study the characteristics of natural lefties who convert. In Brazil, switching is an active practice. But even though many people change their writing hand, the researchers have found, other behaviours remain firmly left-handed2.

The new study could reveal things about the brain beyond its involvement in handedness, says Klöppel. It shows how flexible the brain is in terms of which regions can do what, for example. "The key thing is that there are areas that can be influenced by training and areas that resist this," he says. "It's not only interesting in regard to handedness, but also in terms of plasticity."

Test your own handedness with the Edinburgh Handedness Inventory

References

  1. Klöppel, A. et al. J Neurosci 27, 7847-7853 (2007).
  2. Porac, C. & Martin, W. Laterality 12, 273-291 (2007).

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