These four studies have used two main operationalisations of “cognitive resilience”: (1) The absence of dementia or mild cognitive impairment (MCI) in older age13,14 and (2) cognitive performance or trajectory in APOE ɛ4 carriers (e.g. cognitive performance in the highest tertile among APOE ɛ4 carriers)12,15. Here, APOE is linked to Cognitive impairment.