Background. Brain reserve is a property of the central nervous system related to complex mental activity which may mediate the course and clinical expression of brain injury. Since there is no instrument that comprehensively assesses complex mental activity through the lifespan, we developed and tested the Lifetime of Experiences Questionnaire (LEQ) in a prospective study of healthy ageing.

Method. The LEQ assesses educational, occupational and cognitive lifestyle activities at different stages through life. Test–retest, item analysis and Item Response Theory (IRT) were used to determine reliability. Dimensionality was evaluated using factor analysis. Validity was established through IRT analysis of test performance, correlation with an extant contemporaneous instrument (Cognitive Activities Scale; CAS) and prediction of global cognitive change over 18 months controlling for age, baseline cognition and hypertension.

Results. In a sample of healthy older individuals (n=79) the LEQ was found to be consistent, coherent and discriminate between individuals with high and low mental activity levels. Factor analysis revealed a dominant factor which loaded heavily on education, occupation and leisure activity. Total LEQ was significantly correlated with the CAS. Furthermore, individuals with higher LEQ scores showed less cognitive decline over 18 months, independent of covariates (r=0·37, p=0·003).

Conclusions. The LEQ is a reliable and valid instrument for assessing complex lifespan mental activity which is protective against cognitive decline. The LEQ is therefore proposed as a useful tool for estimating brain reserve in older individuals and further development is anticipated.