[Definition and prevalence of mild cognitive impairment]

Cognition is the ability that allows humans to carry out their lives without difficulty, resolving problems and situations, and to continue to learn and correctly process information from the environment for its subsequent retrieval and use. In persons with normal or physiological brain ageing, this ability is maintained throughout their lives. However, individuals with abnormal or pathological ageing could be affected by distinct degrees of impairment of higher brain functions. The term mild cognitive impairment (MCI) entered the lexicon in 1988 to describe a syndrome encompassing greater than expected cognitive impairment for the person's age and cultural environment. At that time, MCI was considered a degenerative process that preceded dementia. In the last 30 years, it has become clear that not all patients with MCI will progress to dementia. Therefore, the concept and definition of this syndrome have been constantly updated, and distinct subtypes of MCI have been established according to the affected cognitive domain. There is a need to define MCI more clearly and identify its subtypes in order to establish its impact on an ageing society, identify persons at risk of progressing to dementia, and implement early intervention strategies aimed at improving the mental health of the elderly population.