Why is it so hard to learn a new language? Scientists blame the brain

And the reason children actually have a biological advantage.

Monisha Ravisetti Former Science Writer
Monisha Ravisetti was a science writer at CNET. She covered climate change, space rockets, mathematical puzzles, dinosaur bones, black holes, supernovas, and sometimes, the drama of philosophical thought experiments. Previously, she was a science reporter with a startup publication called The Academic Times, and before that, was an immunology researcher at Weill Cornell Medical Center in New York. She graduated from New York University in 2018 with a B.A. in philosophy, physics and chemistry. When she's not at her desk, she's trying (and failing) to raise her online chess rating. Her favorite movies are Dunkirk and Marcel the Shell with Shoes On.
Monisha Ravisetti
3 min read

Matt Leonard, assistant professor of neurological surgery at UCSF, reviews data from electrocortical recordings made during work with epilepsy patients.  

Susan Merrell

The brain lives in a state of constant flux. It repeatedly adjusts itself to enhance our mental performance while juggling millions of incoming signals. While that adaptability keeps us cogent, however, scientists say it's precisely what makes it so difficult for adults to learn new languages.

Brain cell activity can be divided into two categories -- plasticity and stability. Plasticity refers to the brain's ability to change. As we gain new information, we form new connections between neurons. Stability is the opposite; it allows the brain to hold on to things we've already learned, to make those connections stick.

Younger children have a high level of "neural plasticity." Forming new neural connections is useful for kids because they need to learn tons of novel information and discern what's important enough to hold on to. But as we get older, the brain's ability to make new connections naturally decreases. Neural plasticity goes down.

"The brain starts to prioritize stability," explained Matt Leonard, assistant professor in the Department of Neurological Surgery at the University of California at San Francisco. "We basically want to hang on to the important stuff that we've spent the last decade or more learning." 

When learning a new language, humans rely on plasticity, according to new research published Monday in Proceedings of the National Academy of Sciences. That's why kids can often pick up multiple languages with little effort, while adults tend to struggle to get a few Duolingo lessons down. 

To understand how the brain might pick up a foreign lexicon, UCSF neuroscientists studied the brain activity of 10 English-speaking epileptic patients while the subjects learned Mandarin. These volunteers already had electrodes in their brain due to their condition and consented to extend the devices' data to the project, offering a unique opportunity for researchers to directly study the human brain as it learns.

Upon completing analysis of the subjects' brain data, Leonard and fellow researchers found that "knobs" of neurons -- within the region of the brain known as the speech cortex -- were active during the learning process. That means some neurons didn't participate.

"There are these different sorts of groups of neurons, some of which seem to be really willing to change with learning and others that are more resistant," Leonard said.

He notes the team selected Mandarin as the "new" language for the study because its sounds greatly contrast with the cadences of English. That makes it more challenging for English speakers to learn because it requires them to form a huge number of new neural connections.

Our brains are more likely to pick up familiar sounds, another reason surrounding ourselves with a language is often more effective than formal lessons. It all has to do with training our brains to recognize patterns and engage our neurons.

"The best way to learn a new language, whether you're a kid or an adult, is to be immersed in it," Leonard said, "to be around native speakers as much as possible."

He also stresses that during any learning process, there will be ups and downs. In fact, brain activity data of the study subjects indicated large variations in learning success.

"There might just be time periods where the stability neurons just kind of went out and they might just say, 'Look, we need to slow this down and not change things too much right now,'" Leonard explained.

But when things get tough, the key is to remain motivated. It might be in our best interest to keep our COVID-19 lockdown-motivated French lessons going, even if the only word we can say with any semblance of confidence a few months in is bonjour.

"If you're in the process of learning," Leonard said, "and you start to feel like, 'I'm like not getting this, I'm starting to lose what I'm supposed to be paying attention to,' and your motivation goes down, you're actually not going to do as well."