When British neurosurgeon Henry Marsh sat at his patient’s bedside after surgery, he knew the bad news he was about to deliver was his own mistake.
The man had a trapped nerve in his arm that required surgery, but after making a midline incision in his neck, Marsh punctured the nerve on the wrong side of his spine.
Preventable medical errors often have to do with surgery done on the wrong side: an injection in the eye that was not, for example, or a breast biopsy that was not.
These “never events” (a medical jargon term for serious and largely preventable patient safety accidents) highlight that while most of us learn left from right as children, not all of us do it well .
While for some people telling left from right is as easy as telling top from bottom, a significant minority (about 1 in 6 people, according to a recent study) have difficulty with the distinction.
Even for those who think they have no problems, the distractions like ambient noise or having to answer unrelated questions with what is being done can get in the way of making the right decision.
“Nobody has a hard time telling (that something is) back and forth, or up and down,” says Ineke van der Ham, an assistant professor of neuropsychology at Leiden University in the Netherlands.
But differentiating the left from the right is different. “It’s because of the symmetry, and because when you turn around, it’s the other way around, and that makes it very confusing.”
Multiple parties involved
Distinguishing between left and right is actually quite a complex process, requiring memory, language, visual and spatial processing, and mental rotation.
In fact, researchers are just beginning to get to the bottom of what exactly happens in our brains when we do it, and why it’s so much easier for some people than others.
“Some people can innately tell right from left, they can just do it without thinking,” says Gerard Gormley, a physician and professor at Queen’s University Belfast in Northern Ireland. “But others they have to go through a process“.
In an effort to understand what happens in medical errors involving the wrong side, Gormley and colleagues conducted research on the experience of medical students making left-right decisions and examined the process.
“First of all, you have to orient yourself from right to left,” he says.
When the answer doesn’t come instantly, participants described various techniques, from making an L with their thumb and forefinger to thinking about what hand does he useno to write or play the guitar. “For some people it’s a body tattoo or piercing,” says Gormley.
Then, when you figure out which side another person is left or right, the next step is to mentally turn to face the same direction as the other person. “If I’m facing you, my left hand will be facing your right hand,” says Gormley.
“That idea of mentally rotating an object adds an extra degree of complexity.”
Other research shows that people find it easier to judge whether an image shows a left or right hand by imagining their own hand or body spinning.
A percentage
Research published by Van der Ham and colleagues in 2020 found that around 15% of people rate themselves insufficient when it comes to identifying left and right.
Nearly half of the 400 study participants said they used a hand-related strategy to identify which is which.
The researchers used something called the Bergen Right-Left Discrimination Test to dig deeper into how these strategies work.
Participants looked at images of people drawn as stick figures. Some figures looked towards them and others did not and they had their arms in various positions, and they had to identify the hand that stood out as the left or the right.
“It sounds simple, but it’s a bit frustrating if you have to make 100 of these as quickly as possible,” Van der Ham says.
In the first experiment, the participants sat with their hands on a table in front of them.
“There was a very clear effect in the way this little stick figure was placed,” Van der Ham says.
“If you looked at the back of the head, so it was in line with you, people were much faster and more accurate.”
Similarly, when the stick person was facing the participant but had their hands crossed, so that their left hand was on the same side as the participant’s left hand, people tended to do better.
“That tells us that the body is really involved on this,” says Van der Ham.
Strategies
The next question was whether the participants were using signals from their body at the time of the test to identify left and right, or whether they were referring to a stored idea about their body.
To answer that, the researchers repeated their experiment, but this time they tested four different scenarios: Participants sat with their hands crossed or uncrossed on the table in front of them, and had their hands visible during the test or covered with a cloth. black. towel.
But the researchers found that none of those changes influenced the performance of the test. In other words, the participants did not need to see their hands to use their own bodies to tell right from left.
“We have not fully resolved the issuesays Van der Ham. “But we were able to identify our bodies as a key element in recognizing left from right, and we consulted our body representation as we have it in a more static way.”
In Van der Ham’s experiments, the increase in performance that resulted from being in line with the stick figure was most pronounced in people who said they use a hand-related strategy to differentiate left from right in their lives. daily, as well as in women in general.
The researchers also found that men tended to respond faster than women, but the data did not support previous studies showing that men perform better overall on tests of left-right discrimination.
It’s not clear exactly why people differ in their ability to tell left from right, although research indicates that the more asymmetrical someone’s body is (in terms of hand preference for writing, for example), the easier it is for them to write. turns out to differentiate left and right.
“If one side of your brain is slightly larger than the other, you tend to have better right-left differentiation,” Gormely says.
The firsts years
But it could also be something we learn in childhood, like other aspects of spatial cognition, Van der Ham says.
“If kids are in charge of finding the way, if you just let them walk in front of you a few feet and make the decisions, those are the kids who end up being better navigators,” she says.
Research by Alice Gomez and colleagues at the Lyon Neuroscience Research Center in France suggests that left-right discrimination is something children can quickly learn.
Gomez designed a two-week, teacher-led intervention program to increase children’s body representation and motor skills. children from five to seven years.
When their ability to locate the correct body part on themselves or a partner (their right knee, for example) was tested after the program, the number of left-right differentiation errors was nearly halved.
“It was very easy for us to increase the children’s abilities to be able to locate the (body part) based on name,” says Gomez.
One reason for this could be that the children were taught a strategy: to think of the hand they use to write, when they could not remember the right and the left.
The show’s focus on children’s own bodies is another possible explanation, especially since other research shows that an egocentric frame of reference is key when we make decisions from left to right.
In a typical classroom, children may label body parts on a diagram instead of their own bodies, because the latter is more time-consuming and more difficult for a teacher to assess, Gomez says. “It’s very rare that they have time to be self-centered,” she says.
the most challenging
While there are many everyday scenarios where it’s important to tell left from right, there are some situations where it’s absolutely vital.
Neurosurgeon Marsh was able to correct his trapped nerve surgery, but a surgeon removing the wrong kidney or amputating the wrong limb, for example, would have devastating consequences.
Medicine isn’t the only field where left-right mistakes can mean the difference between life and death: it’s possible that a helmsman turning the ship to the right instead of the left was a contributing factor. to the sinking of the Titanic.
But while some people have to work harder to distinguish left from right, everyone has the ability to err in left-right decisions, Gormley says.
The specialist hopes that a increased awareness of how easy it is to make such a mistake lead to less stigma for those who need to verify their decision.
“As healthcare professionals, we spend a lot of time labeling spatial orientations—proximal, distal, superior, inferior—but we don’t really pay attention to left or right,” he says.
“And actually, of all the spatial orientations, that’s the most challenging.”
a different brain
About one in 10 people is left-handed, and twin studies have shown that genetics play a part.
A study from the University of Oxford recently revealed four regions in DNA that seem to play a role in determining whether someone is left-handed or right-handed.
Those who were left-handed were found to have “mutations” in four genes that code for the body’s cytoskeleton, the complex scaffolding found inside cells to help organize them.
Scanning studies of people with these mutations showed that the white matter in their brains had a different structure.
The left and right sides of the left-handed people’s brains were also better connected than in right-handed people.
*This note was originally published in English on BBC Future
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