Maria Konnikova examines the research of Angela de Bruin:
De Bruin isn’t refuting the notion that there are advantages to being bilingual: some studies that she reviewed really did show an edge. But the advantage is neither global nor pervasive, as often reported.
Where learning another language does pay dividends:
One of the areas where the bilingual advantage appears to be most persistent isn’t related to a particular skill or task: it’s a general benefit that seems to help the aging brain. Adults who speak multiple languages seem to resist the effects of dementia far better than monolinguals do.
When Bialystok examined the records for a group of older adults who had been referred to a clinic in Toronto with memory or other cognitive complaints, she found that, of those who eventually developed dementia, the lifelong bilinguals showed symptoms more than four years later than the monolinguals. In a follow-up study, this time with a different set of patients who had developed Alzheimer’s, she and her colleagues found that, regardless of cognitive level, prior occupation, or education, bilinguals had been diagnosed 4.3 years later than monolinguals had. Bilingualism, in other words, seems to have a protective effect on cognitive decline. That would be consistent with a story of learning: we know that keeping cognitively nimble into old age is one of the best ways to protect yourself against dementia. (Hence the rise of the crossword puzzle.) When the brain keeps learning, as it seems to do for people who retain more than one language, it has more capacity to keep functioning at a higher level.