Posts tagged hand preference
Articles and news from the latest research reports.
Babies Don’t Develop Handedness All At Once
Reaching for Froot Loops and grabbing Lego pieces to build a tower are different challenges for toddlers. Depending on what they’re trying to do, tots tend to develop handedness for different tasks at different ages, according to new research.
Most people are right-handed. Babies start using their right hand to reach for cereal nuggets by age 1. However, children take until age 4 to show such a preference when building Lego models. The findings, published in this month’s issue of Developmental Psychobiology, imply tendencies to use one hand more than the other emerge depending on the tasks kids confront, rather than their age.
Preference for the right or left hand is, in part, genetic. Prior studies have shown that some of these one-sided tendencies emerge early. Fetuses suck their right thumb more often than their left; newborns on their back turn to the right more frequently. Most children grow up to be right-handed—in part because of these innate, early leanings, scientists believe.
But the timing of when one hand emerges as the dominant one for most tasks remained unclear.
"As a parent and a scientist, I was surprised to find researchers thought 3-year-olds don’t display a hand preference," said neurobiologist Claudia Gonzalez of the University of Lethbridge in Alberta, Canada.
To study how handedness emerged between ages 1 to 5, Gonzalez and her colleagues assigned about 50 tiny participants to a familiar task: grabbing a colorful object or a tasty tidbit. Children ages 1 to 2 picked up Froot Loops or Cheerios to munch at snack time. Four- and 5-year-olds grasped Lego blocks to build a small model. Three-year-old subjects tackled both tasks.
Even the youngest children had strong right-handed leanings when reaching for food, the team found. Three-year-olds were right-handed eaters, but they were just as likely to use their left hand when playing with blocks. The 4- and 5-year-olds used their left hand to hold the base of their model steady, but they manipulated blocks into the correct positions with their other hand—a clear preference for right-handedness.
"There is a developmental milestone between the ages of 3 and 4 when something clicks," Gonzalez said. "Maybe they become more skilled, or they understand the task better."
Until that developmental “click,” this study shows hand preference isn’t constant across tasks – regardless of a child’s age.
The study “uses a very clever design to get at the question of how handedness varies across tasks,” said Klaus Libertus, an infant development researcher at the University of Pittsburgh. “We did not know handedness is connected to tasks in this way. I would have expected the 3-year-olds to show the same pattern on both tasks, especially since the demands were so similar.”
Developing a hand preference might also correlate with other functions that rely strongly on just one side of the brain, such as language and certain decision-making skills, Gonzalez noted. Preliminary data from children in her lab suggests that when handedness is evident earlier, these other functions also mature more quickly.
Finding the right task to study handedness at different ages will give researchers a firmer grasp on how young brains develop right - or left -handed tendencies, she said.
"You could say hand preference develops before 1, or you could say it doesn’t emerge until age 4—just depending on what task you are looking at," said Gonzalez.
(Source: livescience.com)
Genes for body symmetry may also control handedness
Lefties and righties can thank same DNA that puts hearts on left side for hand dominance
Left- or right-handedness may be determined by the genes that position people’s internal organs.
About 10 percent of people prefer using their left hand. That ratio is found in every population in the world and scientists have long suspected that genetics controls hand preference. But finding the genes has been no simple task, says Chris McManus, a neuropsychologist at University College London who studies handedness but was not involved in the new research.
“There’s no single gene for the direction of handedness. That’s clear,” McManus says. Dozens of genes are probably involved, he says, which means that one person’s left-handedness might be caused by a variant in one gene, while another lefty might carry variants in an entirely different gene.
To find handedness genes, William Brandler, a geneticist at the University of Oxford, and colleagues conducted a statistical sweep of DNA from 3,394 people. Statistical searches such as this are known as genome-wide association studies; scientists often do such studies to uncover genes that contribute to complex diseases or traits such as diabetes and height. The people in this study had taken tests involving moving pegs on a board. The difference in the amount of time they took with one hand versus the other reflected how strongly left- or right-handed they were.
A variant in a gene called PCSK6 was most tightly linked with strong hand preference, the researchers report in the Sept. 12 PLOS Genetics. The gene has been implicated in handedness before, including in a 2011 study by the same research group. PCSK6 is involved in the asymmetrical positioning of internal organs in organisms from snails to vertebrates.
Brandler, who happens to be a lefty, knew the gene wasn’t the only cause of hand preference, so he and his colleagues looked at other genetic variants that didn’t quite cross the threshold of statistical significance. Many of the genes the team uncovered had previously been shown in studies of mice to be necessary for correctly placing organs such as the heart and liver. Four of the genes when disrupted in mice can cause cilia-related diseases. Cilia are hairlike appendages on cells that act a bit like GPS units and direct many aspects of development of a wide range of species, including humans.
One of the cilia genes, GLI3, also helps build the corpus callosum, a bundle of nerves that connects the two hemispheres of the brain. Some studies have suggested that the structure is bigger in left-handers.
It’s still a mystery how these genes direct handedness, says Larissa Arning, a human geneticist at Ruhr University Bochum in Germany. In addition to genes that direct body plans, she says, the study suggests that many more yet-to-be-discovered genes probably play a role in handedness.
Brandler hopes the study will also help remove some of the stigma of being left-handed. Left-handedness isn’t a character flaw or a sign of being sinister, he says: “It’s an outcome of genetic variation.”
(Source: sciencenews.org)
Right-Handed Males, Left-Handed Females?
This is true for sugar gliders (Petaurus breviceps) and grey short-tailed opossums (Monodelphis domestica), say biologists from Saint Petersburg State University, Russia.
Their study, published in the open access journal BMC Evolutionary Biology, shows that handedness in marsupials is dependent on gender.
This preference of one hand over another has developed despite the absence of a corpus callosum, the part of the brain, which in placental mammals allows one half of the brain to communicate with the other.
Many animals show a distinct preference for using one hand (paw, hoof) over another. This is often related to posture – an animal is more likely to show manual laterality if it is upright, related to the difficulty of the task, more complex tasks show a handed preference, or even with age. As an example of all three: crawling human babies show less hand preference than toddlers.
Some species also show a distinct sex effect in handedness but among non-marsupial mammals this tendency is for left-handed males and right-handed females.
In contrast, the team from Russia shows that male quadruped marsupials, such as who walk on all fours, tend to be right-handed while the females are left-handed, especially as tasks became more difficult.
“Marsupials do not have a corpus callosum – which connects the two halves of the mammalian brain together. Reversed sex related handedness is an indication of how the marsupial brain has developed different ways of the two halves of the brain communicating in the absence of the corpus callosum,” explains senior author Dr Yegor Malashichev.