Left hand, right brain - but which comes first?

Friday is International Left-Handers Day. It coincides with new research suggesting that handedness is decided in the womb, reports Louise Holden.

Until recently, it was widely believed that children did not settle on a dominant hand until they were two or three years old. However, a team from Belfast's Queen's University has been studying foetuses in the womb and after birth, and has concluded that the hand that is most active in 10-week-old foetuses is the hand they will favour for the rest of their lives.

The research, reported by New Scientist magazine, identified 60 foetuses who sucked their right thumb in the womb, and 15 who sucked their left thumb. When the babies were examined again between the ages of 10 and 12, the researchers found that all 60 of the right thumb suckers were now right-handed. Two-thirds of the left thumb suckers were left-handed, the rest apparently having switched their dominant hand.

At 10 weeks old foetuses are too young to have begun to suck their thumbs, but they do wave their hands about. The Belfast team found that the majority tend to wave their right arm more than their left. Lead researcher Prof Peter Hepper said that movements at 10 weeks are not under brain control. This would suggest that handedness may be determined by local spinal chord reflexes rather than by brain architecture.

If this turns out the be the case, it casts a different light on our understanding of the connection between brain architecture and handedness. The left side of the body is governed by the right side of the brain, and vice-versa. Until now, it was widely believed that left-handedness developed as a result of a better developed right-brain function. The right side of the brain is associated with creative mental activity - hence the idea that left-handers are more artistic than right-handers.

This new research suggests that the opposite effect might be at work. If handedness is established before the brain develops, then the development of the brain might well be influenced by handedness, rather than the other way around.

Up to 15 per cent of the world's population is thought to be left-handed, and the rate is higher among boys and twins. Historically, left-handedness was seen as a curse, and the negative connotations lingered until the 1950s in Ireland, with left-handed children being forced to write with their right hands in school. Some Irish parents are the products of those times and still have writing problems as a result.

Interfering with handedness at a young age has been known to have a negative effect on cerebral organisation. Children whose handedness is "corrected" can suffer from from stuttering, poor vision and reduced visual/spatial processing. Most end up with mixed handed aspects for the rest of their lives.

Luckily, left-handedness is now accepted as normal and Friday will see left-handers all over the world (but mainly in the US) celebrating their right-brain dominance. Famous left-handers who have become mascots for the movement include Marilyn Monroe, Leonardo da Vinci, Albert Einstein, Jimi Hendrix, Martina Navratilova, Nicole Kidman and The Simpsons' Ned Flanders.

A child's handedness is usually not distinguishable until three years old. However, there is a theory that you can tell which hand a child will favour by the direction of hair growth on the crown of his or her head. If the hair grows clockwise, it is said that the child will be right-handed; if it grows anti- clockwise, left-handed.

Right-handed parents of left-handed children (and vice-versa) can sometimes encounter difficulties when teaching their children basic skills based on dexterity, such as tying a shoelace. The trick is to position yourself opposite left-handed children while demonstrating, providing a mirror image for them to copy.

For more on International Left-Handers Day, go to www.left-handersday.com