[ti:Study Aims to Find Out Why Some People Are Left-handed]
[al:Science & Technology]
[ar:VOA]
[dt:2024-04-10]
[by:www.voase.cn]
[00:00.00]What do Lady Gaga, Barack Obama, and Bill Gates have in common - aside from their fame? They are all left-handed.
[00:10.74]But why are 10 percent of people left-handed while most are right-handed?
[00:17.93]Researchers are trying to find out.
[00:21.65]A recent study identified a genetic cause of left-handedness in some people. 
[00:28.50]Researchers found rare variants of a gene involved in controlling the shape of cells. 
[00:37.02]They found the variants to be 2.7 times more common in left-handed people.
[00:44.13]These genetic variants account for possibly 0.1 percent of left-handedness. 
[00:52.33]But the researchers said a gene, called TUBB4B, might play a part in the development of brain asymmetry.
[01:03.64]In most people, the two halves, or hemispheres, of the brain have slightly different structures and are dominant for different activities.
[01:16.37]"For example, most people have left-hemisphere dominance for language, and right-hemisphere dominance for tasks that require directing visual attention to a location in space," said Clyde Francks of the Max Planck Institute for Psycholinguistics in the Netherlands. Francks was the top writer of the study published recently in Nature Communications.
[01:45.28]Francks suggested that for most people, the left side of the brain controls the dominant right hand. 
[01:54.28]"The nerve fibers cross from left-to-right in the lower part of the brain," Francks said.
[02:02.05]He added, "In left-handers, the right hemisphere is in control of the dominant hand. 
[02:09.97]The question is: what causes the asymmetry of the brain to develop differently in left-handers?"
[02:18.68]TUBB4B controls a protein that gets formed into filaments called microtubules. 
[02:27.87]These microtubules give structure to the insides of cells.
[02:33.98]The changes in TUBB4B that are more common in left-handers suggest that microtubules are involved in setting up the brain's normal asymmetries, Francks said.
[02:48.79]The two brain hemispheres start to develop differently in the human embryo. Scientists do not know the mechanism that controls this.
[03:00.42]"Rare genetic variants in just a handful of people can pinpoint genes that give clues to developmental mechanisms of brain asymmetry in everyone," Francks added. TUBB4B is an example.
[03:19.32]The study's findings were based on genetic data from more than 350,000 middle-aged to older adults in Britain. 
[03:31.11]It was from the UK Biobank. About 11 percent of the people involved were left-handed.
[03:39.51]For most people, left- or right-handedness might come down to chance.
[03:46.04]Changes in the levels of some molecules during important times of brain development could influence it, Francks suggested.
[03:56.11]Historically, many cultures disapproved of left-handedness and forced people to become right-handed.
[04:05.58]In English, the word "right" also means "correct" or "proper." And the expression a "left-handed compliment" means that a comment might seem nice but is an insult.
[04:20.62]The levels of left-handedness differ around the world, with lower rates in Africa, Asia and the Middle East compared to Europe and North America, Francks said.
[04:33.98]"This likely reflects suppression of left-handedness in some cultures - making left-handed kids switch to right-handedness, which also used to happen in Europe and North America," Francks added.
[04:50.81]The new findings might have use in the field of mental health.
[04:55.36]People with schizophrenia are around twice as likely to be left-handed or ambidextrous. 
[05:02.49]People with autism are around three times as likely, Francks said.
[05:07.61]He observed that genes involved in developing the brain in early life might be involved in brain asymmetry and mental health.
[05:18.86]"Our study found suggestive evidence of this, and we have also seen it in previous studies where we looked at more common genetic variants in the population," Francks added.
[05:32.10]I'm John Russell.