Storage and executive components of working memory: integrating cognitive psychology and behavior genetics in the study of aging.

We combined experimental cognitive and behavior genetic methods to investigate storage and executive components of working memory in 663 middle-aged male twins. A single latent factor model indicated that digits forward (storage) and two-digit transformation (executive + storage) scores were influenced by the same genes. Additional executive demands in digit transformation appeared to increase the variance of individual genetic differences from 25% for digits forward to 48% and 53% for the digit transformation scores. Although it was not the best model, a two-factor model also provided a good fit to the data. This model suggested the possibility of a second set of genes specifically influencing the executive component. We discuss the findings in the context of research suggesting that new genetic influences come into play if demand continues to increase beyond a certain threshold, a threshold that may change with task difficulty and with age.