Bilinguals use two different language systems to mediate not only social communication, but also cognitive processes. Potential differences between bilinguals and monolinguals in task-solving strategies and patterns of cognitive decline during normal and abnormal aging have been suggested.
A research review of the area suggests that normal aging is associated with increased interference between the two languages and tendency to retreat to a single language. General cognitive functioning has been found to be higher in demented bilingual patients if communication is carried out in L1 rather than in L2. Recent research has reported that bilingualism can have a protective effect during aging, attenuating the normal cognitive decline associated with aging, and delaying the onset of dementia.
Regardless of the significant heterogeneity of bilingualism and the diversity of patterns in language use during life-span, current research suggests that bilingualism is associated with preserved cognitive test performance during aging, and potentially can have some protective effect in dementia.