When you write a note, what hand do you use?
How about when you catch a ball or open a jar?
Pretty much everyone knows what it means to be right- or left-handed.
But why are so few people left-handed?
And what's going on in the brain?
Hey there!
I’m Alie Astrocyte.
Let’s talk about the neuroscience of handedness.
Like around 90% of the world’s population, I’m right-handed.
But if you’re left-handed, you’re not alone.
About 10% of the population, or around 700 million people, are just like you.
And a very small number of people are somewhere in between.
Either cross-handed, where their dominant hand varies based on the task, or truly ambidextrous,
where they can use either hand equally well for pretty much anything.
It’s pretty unclear how different people end up with different dominant hands, but
there does seem to be some sort of genetic component.
Left-handedness is more common in males.
And if both of your parents are left handed, there’s about a 26% chance that you’ll
be left handed, too.
And scientists have found connections between being left handed and differences in genes
having to do with left-right asymmetry.
What the heck is that?
Well, in general, we’re pretty symmetrical creatures.
But, there are a few things that have to be asymmetric.
Like our hearts and our guts.
So left-handedness could be a product of tiny changes in a bunch of these genes, but we’re
still not exactly sure what makes a person left-handed.
There’s also some evidence that handedness could be influenced by exposure to different
hormone levels in the womb, like androgen hormones, which may be why women who are left
handed have a higher risk for breast cancer.
What does this have to do with the brain?
Like our hearts and our guts, our brain is somewhat asymmetrical.
That means that some things are only on one side or the other.
Scientists know that there seems to be a connection between your handedness and lateralization.
That is, which side of your brain processes different tasks.
Now, I’m not talking about things like being “left brained” or “right brained”.
It’s a myth that being creative or analytical are connected to a “dominant” brain hemisphere.
But there are a few things that one side of your brain tends to control more than the
other.
Like language.
So, since I’m right-handed, it’s really likely that the left side of my brain takes
care of the majority of my language processing.
This is true for about 96% of people who are right-handed.
But on the flip side, someone who’s left-handed has a nearly 30% chance of having language
controlled mostly by the right hemisphere.
As I mentioned in our language video, for most people, the left hemisphere handles most
of the language tasks.
But people who are left handed are more likely to have a more mixed up arrangement, with
both sides of the brain becoming active during language processes.
A small fMRI study looking at brain activation during a memory task found some differences
related to handedness, too.
In a task where people had to remember and recall paired sets of words, participants who were
left-handed had more activation in their left hippocampus and amygdala than those who were
right handed.
It needs more work, but this is some of the first evidence that memory might also be lateralized
in the brain.
You may have heard that being left handed means you’re more likely to be a genius.
After all, lots of brilliant people are left handed.
Like Michelangelo, Hellen Keller, Bob Dylan, and Barack Obama.
There are even websites that claim that “20% of Mensa’s members are left handed”.
But...sorry, lefties.
That’s a myth.
Research hasn’t found any significant difference in intelligence between people who are left
or right handed.
If anything, there’s a slight benefit to being right handed.
But it’s really hard to even say much about the pros or cons of being left-handed because
it’s so understudied.
Unfortunately, people who are left handed are often excluded from scientific studies,
because handedness might add a confound to the research.
That is, an unknown effect of being left-handed could influence the outcome of the study.
So there are a lot of unanswered questions when it comes to handedness and the brain.
But it’s still a curious thing.
And there are researchers out there who are trying to figure it out.
It’s especially interesting because we don’t understand the role of lateralization in general.
Why are our brains asymmetrical?
And how does that influence our behavior and personalities?
Eventually, we might be able to figure it out.
And find out what other interesting traits are tied to handedness.
Thanks for watching this episode of Neuro Transmissions!
Until next time, I’m Alie Astrocyte.
Over and out!