Genetic and environmental architecture of processing speed across midlife

Abstract

Objective: Processing Speed (PS) is an important domain in cognitive aging that is characterized by multiple related but nonidentical abilities. Few studies have directly investigated the relationships among PS measures, and none have used genetically informed methods. In this study, we examined the relationship between measures of PS at up to two time points during middle age.

Method: We examined data from 1,262 middle-aged men when the sample was at a mean age of 56 and a mean age 62 years. Participants completed 6 measures of PS from three different cognitive tests. We used a genetically informative, confirmatory factor analytic approach to evaluate the phenotypic and genetic relationships cross-sectionally at both single time points and across time.

Results: A higher-order common PS factor accounted for the covariance among three test-specific factors, and each test-specific factor accounted for the covariance between two observed measures. The general PS factor was explained primarily by genetic influences at both time points (a²_age56 = .75, a²_age62 = .64), and all test-specific factors were heritable (a² range: .45 to .65). Factor loadings from the test-specific factors to the general PS factor varied from λ = .46 to .82. The model was stable over time, although there were differing rates of phenotypic change among latent factors (.20 SD to .44 SD). Cross-time genetic correlations were near unity for all latent factors.

Conclusion: These results suggest that PS is highly heritable when considered at a latent variable level, and that there are different rates of change in tests of PS within this sample. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Figure 1:

Wave 1 Higher Order Factor model. Standardized variance components are presented; “A” indicates the heritability of the related factor, “C” indicates the common environmental influences, and “E’ indicates the unique environmental influences. As explained in the footnote above, the standardized variance components for the test-specific factors can be calculated via the hierarchal common pathways.

Figure 2:

Unrestricted longitudinal model. Standardized variance components are presented; “A” indicates the heritability of the related factor, ”C” indicates the common environmental influences, and “E’ indicates the unique environmental influences. As explained in the footnote above, the standardized variance components for the test-specific factors can be calculated via the hierarchal common pathways. Significant estimates are bolded. For readability, the figure does not include standardized variance components for the common environmental influences on the Trails factors (C_trl) or label the residual influences on the observed variables.