Am I too old to learn a new language?

When Adrian Black met his Italian partner 10 years ago, he was determined to learn her home language. Having successively picked up French a decade earlier when he lived in France, he felt the challenge was attainable.

"I was blown away by how hard it was to learn French, but I came back speaking it pretty well," says Black, who is now 50. But getting to grips with Italian has been a much tougher process, he explains: "I feel like French is deep down in my head somewhere, but with Italian it will take a lot more effort for me to get to that level. "I've noticed that my brain isn't as good as it was, and I'm pretty sure I don't retain stuff as well as I used to. It just doesn't all click as easily as it used to."

It's often said that you can't teach an old dog new tricks. Actually this proverb is, for the most part, not true. For much of the history of modern neuroscience, the adult brain was believed to be a fixed structure that, once damaged, could not be repaired. But research published since the 1960s has challenged this assumption, showing that it is actually a highly dynamic structure, which changes itself in response to new experiences, and adapts to injuries – a phenomenon referred to as neuroplasticity.

Collectively, this body of research suggests that one can never be too old to learn something new, but that the older they are, the harder it is for them to do so. This is because neuroplasticity generally decreases as a person gets older, meaning the brain becomes less able to change itself in response to experiences.

Some aspects of language learning become progressively more difficult with age, others may get easier. "Older people have larger vocabularies than younger ones, so the chances are your vocabulary will be as large as a native," says Albert Costa, a professor of neuroscience who studies bilingualism at the Universitat Pompeu Fabra in Barcelona. Picking up a new language's vocabulary is much easier for adults than learning the rules that govern its grammar or syntax. This is because new words can be easily mapped on to a learner's pre-existing knowledge. But older learners are less likely to have good pronunciation or accent, since the phonemes, or sounds, of a language are picked up naturally by children.

Learning a new language may not always be easy for adults, but there is research to suggest that doing so is beneficial for brain health. As we get older, most of us experience an age-related decline in mental functions such as attention and memory, and in some people the acceleration of this process leads to the development of Alzheimer's disease or some other form of dementia. A number of recent studies suggest that learning a foreign language can slow this inevitable age-related cognitive decline or perhaps even delay the onset of dementia.

In the largest study of its kind to date, researchers at Edinburgh University examined the medical records of 648 Alzheimer's patients in the Indian city of Hyderabad. They found that the bilinguals developed dementia later than monolinguals, by an average of four-and-a-half years.

We know that education can also delay the onset of dementia, but the researchers also took that into account. "A large part of the population in Hyderabad is bilingual but illiterate, so we compared educated bilinguals with bilinguals who never went to school," says lead researcher, Thomas Bak. The study found that dementia was delayed by an average of six years in uneducated bilinguals, compared to four years in educated bilinguals.

"Learning a language later on in life might be more beneficial than learning it earlier, because it takes more effort," Bak continues. "It has parallels with physical exercise – a stroll is good for your health, but not as beneficial as a run."

Learning – and using – a foreign language seems to improve what psychologists and neuroscientists call executive function, which refers to a hypothetical set of mental processes that enable us to vary our thoughts and behaviours from one moment to the next, depending on the task at hand.

"Using two languages seems to have consequences not only for executive functions, but also for other processes," says Costa. "It's like learning to juggle, the idea being that you have to juggle two balls every time you speak. Some of the work is controversial, so we need more data to have a definite answer."

Despite the difficulties, Black regards learning foreign languages as fun, and treats the endeavour like a puzzle that has to be solved. "I'm doing it partly to keep my brain active," he says. "When you have some success and can express yourself, it feels like you're using different parts of your brain that you weren't using before."

Indeed, research shows that bilingual children use the same brain regions for both languages if they are learned during childhood, whereas learning a second language later on in life recruits different regions from those involved in using one's mother tongue. And learning a foreign language, much like learning to play a musical instrument, does indeed appear to be a good way of exercising one's brain, and keeping it healthy, throughout life.