The Impact of Bilingualism on Cognitive Reserve as a Protectant Against Cognitive Decline

Cognitive decline exists on a spectrum, ranging from mild cognitive impairment to dementia. These two diagnoses encompass a group of symptoms rooted in the progressive decline of cognitive function, impairing aspects like memory, decision-making, language use, and locomotion. This review centers upon the premise of cognitive reserve, an intangible measure of the brain’s resilience and capacity to compensate for damage, and its relationship with the preservation of cognitive function later in life. Bilingualism constitutes one of many contributing factors to a higher cognitive reserve; however, this term fails to reflect the unique linguistic profile intrinsic to every individual—including whether a second language was acquired during childhood or later in life. Therefore, a distinction between “acquired” and “lifelong” bilingualism is made. Through the analysis of task-based and neuroimaging data, this review article elucidates the impact both forms of bilingualism have on cognitive reserve as a protectant against cognitive decline, revealing that resultant neuroprotective advantage is most salient when both languages are used regularly, in diverse environments, and in an active manner. These practices are observed in both acquired and lifelong bilinguals to varying degrees, which are contextualized and explored in detail within the review.