Cognitive abilities change with age. There are individual differences in the timing and trajectory of this change, and hence discovering factors that reduce, delay, or halt cognitive ageing is a research priority. Lifestyle factors, particularly those which are malleable across the life course, may be the most informative in the development of any possible cognitive intervention. Factors of interest include aspects of social, leisure, and physical activity; personality; social networks, support and relationships; diet and nutrition; occupational characteristics and exposures; health behaviours.

Efforts to identify lifestyle factors that are associated with cognitive ageing are complicated by a number of issues. A key concern is being able to distinguish between alternative explanations for a factor's association with cognitive ability. Does the factor lead to differential preservation, that is, does it actually predict subsequent cognitive change, or is the association the result of preserved differentiation, where individuals of a given cognitive ability level are more or less likely to have taken up the lifestyle in the first instance? It is important, though not straightforward, to differentiate between these alternatives given the implications for how the results can be interpreted, and thus used. For example, although leisure-time activities have been consistently associated with cognitive abilities, it remains unclear how much of this effect remains once prior cognitive ability can be accounted for.

Other issues to be addressed in terms of identifying lifestyle predictors of cognitive ageing include the length of followup required to detect cognitive change and possible effects of lifestyle factors, the overreliance on single markers of cognitive ability when this is the key outcome of interest, and whether there are different effects of lifestyle factors during distinct periods across the life course. Original research articles employing diverse methodologies and reviews which seek to examine any of these key issues, and others, are welcomed. No single study will be able to address them all, but the aim of the special issue is to stimulate discussion and further raise awareness of these issues. Potential topics include, but are not limited to:

• Examining multiple cognitive domains and how lifestyle factors might differentially affect these
• Examining the effects of lifestyle factors from across the life course (young adulthood and midlife) on cognitive changes across this same period or through old age
• Reports of intervention studies using the manipulation of any lifestyle factors
• Comparison of the effect sizes on cognitive ageing from different lifestyle factors
• Consideration of the differential preservation versus preserved differentiation debate and ways to address this empirically