No, Brushing Your Teeth Left-Handed Won't Make You Smarter

There’s this idea floating around the web that using your non-dominant hand more often in everyday life will boost your brain power. The supposed lifehack is rooted in the idea of neuroplasticity, or your brain’s innate ability to restructure and rewire itself as you learn or get better at new things. If we could only train up the part of the brain responsible for our oft-neglected left hands, then surely some of that neural enhancement would spill over! Unfortunately, the science behind this idea doesn’t add up.

“I know of no evidence that using the off-hand does any more than increase the skill of that hand,” Michael Corballis, a University of Auckland psychologist specializing in brain asymmetry, tells Inverse by email. “It could be useful, I suppose, if you lose the use of the preferred hand.”

Handedness is determined genetically. While scientists don’t fully understand how people end up dominant in one hand, a prominent theory holds that one genetic variation promotes right-hand preference, while another variation is associated with a 50-50 chance of right-hand preference. There’s also a lot to be said about left-brain- or right-brain-dominance, with fascinating-though-often-overstated theories about left-brainers tending toward logic and language and right-brainers excelling in creativity and intuition. And, yes, that stuff connects to handedness, with the vast majority of right-handers being left-brain dominant, while only around 70 percent of left-handers are left-brain dominant. But, again, there’s no reason to think that using your off-hand more will change handedness or brain orientation.

“Maybe training your left hand to do things the right hand normally does gives a sense of achievement, as the lifehackers blogs seem to say,” Corballis says. “But as a general movement it’s been tried before and quickly fizzled.”

The call to counter handedness has come up time and again throughout history, even attracting visionaries from Plato to Lord Baden Powell, the founder of the Boy Scouts. They all believed that children were born ambidextrous and were corrupted into handedness along the way.

Trying to counter your natural hand preference could do more harm than good, however, especially while the brain is still developing. Children who were born left-handed but forced to develop and use their right hands could have increased rates of mental health problems, according to a 2016 study published in Psychiatry Research.

“There’s also some evidence that ambilaterality may have negative effects, such as confusion over left and right, which can affect things like reading,” Corballis writes. “It might even lead to stuttering, though these symptoms may be more common in people who are born ambidextrous.”

That doesn’t mean that working with your off hand won’t lead to some neurological benefits. One University of Greifswald study from April 2017, which optimistically referred to the hands as “trained” and “non-trained,” found that repeated exercises with the non-trained hand corresponded to increased communication among cells in the brain’s primary motor cortex, which means that the brain got better at controlling that hand with increased practice.

Other studies resulted in similar findings. For example, a research team from the University of Missouri published research in the journal Neuropsychologia in 2016 that found that people who drew with their non-dominant hand for ten days improved their drawing speed and accuracy. MRI brain scans demonstrated corresponding improvements in their brains’ connectivity. These strengthened neural connections allowed for greater performance with the non-dominant hand, and the improvements lasted for another six months after the study participants stopped practicing.

In short, brushing your teeth lefty every day won’t help you ace your math test, but it will help you become a pro at brushing your teeth with your left hand. And hey, that’s something too.