For the first time, we’ve found genes and brain differences linked to left-handedness

For the first time, researchers have been able to highlight specific gene regions that appear to have some influence over left-handedness – and they’ve also found links to differences in brain structure in those who have these genetic variations, too.

It’s already been established that whether we’re right- or left-handed depends to some extent – around 25 percent – on the genetic code we’re born with, but until now scientists hadn’t been able to identify the specific areas on the genome responsible.

This new study of around 400,000 individual records in a national UK database goes a long way to doing just that: it found four genetic regions associated with handedness, and three of those were linked to proteins involved in the brain’s structure and development.

These proteins relate to the cytoskeleton, the scaffolding inside cells that’s responsible for their construction and function.

With the help of brain scans of around 10,000 of the participants, the researchers linked the genetic variations with white matter tracts running between language-processing regions. These white matter tracts contain the cytoskeleton of the brain.

“Many researchers have studied the biological basis of handedness, but using large datasets from UK Biobank has allowed us to shed considerably more light on the processes leading to left-handedness,” says physician Akira Wiberg.

“We discovered that, in left-handed participants, the language areas of the left and right sides of the brain communicate with each other in a more coordinated way.”

That means left handers might have an advantage when it comes to verbal tasks and language skills, Wiberg suggests, though the evidence for that isn’t conclusive.

Humans are pretty unique as far as the animal kingdom goes in having such an imbalance between those of us who are left-handed and those of us who are right-handed – it’s about a 10-90 percent split.

And we know from other animals that cytoskeletal differences – like the coil of a snail’s shell – can be influenced by genetics from very early on. The “hallmarks of the future development of handedness” might develop in the womb, the researchers say, though that’s only a possibility for now.

While it’s still too early to call this a conclusive link between these genes and whether we’re left or right-handed, what the research does do is highlight significant associations between the two that further studies can build on.

We’re finally beginning to make sense of the genetic coding that helps to influence which hand becomes dominant.

It might also help dispel any lingering opinions that being left-handed is somehow unlucky or inferior to being right-handed.

“Here we have demonstrated that left-handedness is a consequence of the developmental biology of the brain, in part driven by the complex interplay of many genes,” says one of the team, Dominic Furniss, a plastic surgeon who researches molecular genetics.

“It is part of the rich tapestry of what makes us human.”

The research has been published in Brain.

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