Cases of language loss and recovery bring up an intriguing paradox. If two languages are stored in the brain, how can it be that a person can lose one of them, but not the other, and then gain one back without relearning it? The traditional models of how a language is represented in the brain suggest that languages can become inaccessible, even though they are not entirely lost. As the author demonstrates through fascinating cases, stress--whether due to foreign language immersion, sleep deprivation, or brain damage--can lead to the apparent loss of one language, but not the other. Arturo...