Why speaking a second language can make you brainier: Bilinguals have 'better memories and problem solving abilities' U.S. researchers believe bilingualism strengthens the brain's executive functions, such as its working memory And bilinguals subconsciously use and control both languages constantly They conducted two experiments to explore whether fluent bilinguals actively chose which language to think and speak in Scientists believe people who can switch between two languages seamlessly, have a higher level of mental flexibility than monolinguals People who can switch between two languages seamlessly have a higher level of mental flexibility than monolinguals, research suggests. Researchers believe bilingualism strengthens the brain's executive functions, such as its working memory and ability to multitask and problem solve. The psychologists think that as fluent bilinguals seem to use both languages at all times but rarely use words unintentionally, they have control of both languages simultaneously. Judith Kroll, professor of psychology, linguistics and women's studies at Penn State University, said: 'Not only is bilingualism not bad for you, it may be really good. 'When you're switching languages all the time it strengthens your mental muscle and your executive function becomes enhanced.' The study, published in Frontiers in Psychology, found fluent bilinguals have both languages 'active' at the same time, whether they are consciously using them or not. Pointing to bilingual people's ability to rarely say a word in the unintended language, the researchers believe they have the ability to control both languages to select the one they want to use without consciously thinking about it. Linguistic researchers at the university conducted two separate but related experiments to explore bilingualism. They studied 27 Spanish-English bilinguals reading 512 sentences in alternating languages who were instructed to read the text silently until they came to words written in red at which point they read them out loud as quickly and as accurately as possible. Bilinguals Bradley Cooper (who speaks French) and Mila Kunis (Russian) could have superior executive functions (such as the ability to multitask and problem solve) compared to monolinguals About half the words written in red were cognates - words that look and sound similar in both languages - and were processed more quickly than other words, according to Jason Gullifer, a graduate student in psychology who was involved with the study. He said the experiment suggests both languages are active at the same time. The participants took part in a similar study but this time read the sentences in one language at a time. The scientists said the results were similar to the first, suggesting the context does not influence word recognition. Mr Gullifer said: 'The context of the experiment didn't seem to matter. If you look at bilinguals there seems to be some kind of mechanistic control.