Age differences in the nature and origin of individual differences in memory: a behavior genetic analysis.

Measures of memory performance and cognitive and lifestyle variables were obtained from 147 younger twin pairs (27 to 60 years) and 194 older twin pairs (60 to 94 years) as part of the Minnesota Twin Study of Adult Development and Aging. Correlational and behavior genetic analyses were combined to investigate age differences in 1) the relationship between memory performance and cognitive and lifestyle variables, 2) genetic and environmental influences on memory performance, and 3) genetic and environmental mediation of the relationship between memory and predictor variables. No age differences in heritability were found. Qualitative age differences in memory processes were suggested by age group differences in the correlations between memory and cognitive factors. Even though age differences in phenotypic correlations had been demonstrated, no age differences in the genetic and environmental mediation of the correlations were found. In other words, the magnitude of the correlation between memory and cognitive factors varied across age groups but the nature of the relationship did not.