The impact of bilingualism on cognitive functions across the lifespan and in brain diseases

The last decades have witnessed fundamental changes in our understanding of both brain and language. In neurosciences, the static localisationist view of a 1:1 correspondence between circumscribed brain areas and specific cognitive functions gave way to a dynamic interaction of multiple networks, in which the same function can be distributed among many areas and the same area can be part of different networks. In parallel, the concept of language as an autonomous, “informationally encapsulated” module has been superseded by the notion of widely distributed language-related brain networks, going well beyond the traditional language areas and interacting with other aspects of cognition.
These advances in the neuroscience of language have been of particular importance for our understanding of bilingualism. Firstly, we came to realise that different languages of a multilingual person cannot be reduced to static representations in isolated brain areas but are subject to parallel activation, inhibition, switching and monitoring within the same brain networks. Secondly, the tension between this parallel activation and a selective output necessary for successful communication constitutes a permanent training for frontal-executive functions. Accordingly, the cognitive effects of bilingualism transcend language itself, leading to a better performance on many executive tasks, particularly those requiring inhibition and switching. This mechanism offers an explanation for a number of recent empirical findings, in which bilinguals were show to be more resistant to cognitive ageing than monolinguals, develop dementia ca. 4 years later and show a significantly better cognitive recovery after stroke.