The mysteries of left- handed people Humans are asymmetric animals. Early in our embryonic development, the heart turns to the left. The liver develops on the right. The left and right lungs have distant structure. There are certain rare syndromes in which the usual asymmetry of organs is reversed. But when it comes to handedness, another basic human asymmetry, which reflects the structure and function of brain, the reversed pattern is relatively common but not easily understood. Over the centuries, left-handers have accused of criminality and dealing with the devil, and children have subjected to “ re-education.” In recent years the stigma vanished; four of American’s last seven presidents- ford. The elders Bush, Clinton – were left – handed. (Reagan is sometimes cited as ambidextrous.) But the riddle of what underlies handedness. Its proportions – roughly 90 percent of people are right handed and 10 percent left- handed – stay consistent over trime. “This is really still mysterious,” said Clyde Francks, a geneticist and the lead author of a 2007 study in which Oxford University researchers identified a genetic variant linked to left- handedness. Hand dominance is related to brain asymmetry. And, Dr. Francks, said “were really at the very beginning of understanding what makes the brain asymmetrical.” There seems to be general consensus that the human brain is profoundly asymmetric, and that understanding that asymmetry will show us much about who we are and how our brains work. Brain lateralization, the distribution of function into right and left hemispheres, is crucial for understanding language, thought memory and perhaps even creativity. For many years, handedness has been seen as a possible proxy, an external due to the balance in the brain between left and right. For right –handed people, language activity is predominantly on the right and left side. Many left-handers also have left –side language dominance, but a significant number have language either more evenly distributed in both hemispheres or else predominantly on the right side. Handedness runs in families. The 2007 paper by the group at Oxford identified a gene, LRRTM1, that they discovered in the course of studying children with dyslexia, and which turned out to be associated with the development of left- handedness. Dr. Francks, who is now at the Max Planck Institute for Psycholinguistic in the Netherlands, recalls that the discovery attracted a great deal of attention because this gene was also found disproportionately in people with schizophrenia, even though none of these connections are simple or well understood. The gene affects the ways neurons communicate with one another, but its mechanisms need to be studied. Because left-handedness has been seen as a key to the complex antomy of the brain, researchers continue to look links to other conditions, including immune disorders, leaning disabilities and dyslexia, reduced life expectancy and schizophrenia. The percentage of left- hander’s in the population seems to be relatively constant, at 10 percent. And this goes back to studies of cave paintings, looking at which hands hunters are using to hold their spears, and to analyses of ancient artifacts. So though there been prejudice against left- hander’s, and though there may be some development risks said Dr. Geschwind, “there clearly must be advantages as well. The reason it maintains that way, nobody knows what it is.
Posted on: Sat, 15 Jun 2013 15:57:30 +0000