World Day of the Zurdería: What causes the left-handed? – Telam

Every August 13, a list of artists, politicians and scientists appears in every newspaper in the world. What do they have in common? All are left-handed and since 1976, we commemorate the World Day of the Zurdería.

Between 10% and 15% of the world's population is left-handed, that is to say that they mainly use the left hand. Although they are no less numerous, left-handers are at a disadvantage in today's societies. So today we are trying to raise awareness of the disadvantages they face in a world designed for right-handed people. From the use of table chairs in colleges and universities, to the modifications of the musical instruments that they wish to play, to the turnstiles of the metro, left-handers are confronted daily with a myriad of deficiencies that make their lives a little more difficult. complicated Although some adaptations have been made in recent years, much remains to be done.

What causes someone to be left-handed?

The brain controls the body crosswise and, almost always, the left hemisphere is the dominant one. In 85% of the population, the left hemisphere, which controls the right hemisphere, proves to be the dominant, that is right-handed. For the remaining 15%, the dominant hemisphere is the right one and these people are left-handed. The probability of being left-handed is greater in men than in women, although the causes are unknown. Even the probability of being left-handed increases by 10% if one of the parents is up and up to 26% if both are. The asymmetry in manual use is already present in the fetus at a very young age. The causes? They are still varied and imprecise. They go from genetic, evolutionary, cultural and environmental explanations to hormonal reactions.

What about the rest of the functions?

In more than 96% of right-wingers, the domains of language processing coincide in the same cerebral hemisphere as manual dominance. In the remaining 4%, the language areas will be located in the right hemisphere, which is contrary to manual dominance. In left-handers, this organization is also different. In more than 60% of cases, the language is located in the left hemisphere, that is, contrary to manual dominance. The probability that the right hemisphere is also dominant for the language reaches 30%. In a certain percentage, this function belongs to both hemispheres, that is to say that it is shared between the two and therefore less vulnerable to its involvement in brain damage.

The choice of the 13th World Day of the Zurdería is not a coincidence. In Latin, the right-handed antonym is ominous. In Spanish, the disaster was ominous and that is why a word in Basque was taken: left / left, to strip it of this negative sense. As far as the southpaw is concerned, the misfortune is linked to the difficulties that left-handers have faced for millennia to adapt to a world of right-handers, forced to use their right hand.

(*) Specialist in clinical neuropsychology (UBA). Lic, phonoudiology (UBA). Director of the Language Neuroscience Research Laboratory of the Foundation of the Institute of Cognitive Neurology (INECO).