First Come, First Served
Languages learned before the age of 5 are represented differently in the brain than are later languages. For example, they trigger sensory associations more actively. Researchers can detect the native tongues among highly proficient bilinguals simply by monitoring neural activity as subjects read.
Lingual Life Extension
Learning a second language can help you out decades down the road. On average, lifelong bilinguals incur dementia four years later than others, adding to the evidence that lifestyle can be more neuroprotective than drugs.
What's It Called?
Don't worry if Johnny loses some English vocab on his trip to France. Research finds that it's not from atrophy of the old tongue; the new one is running interference. To better learn new labels for things, the brain suppresses previously learned terms.
Infants as young as 4 months can tell when a speaker switches languages just by watching the mouth—a marker of how important visual cues are to language learning. But by 8 months only babies raised in bilingual households have this ability; without continued exposure, some perceptual abilities wane.