High-dimensional response growth curve modeling for longitudinal neuroimaging analysis

There is increasing interest in modeling high-dimensional longitudinal outcomes in applications such as developmental neuroimaging research. Growth curve model offers a useful tool to capture both the mean growth pattern across individuals, as well as the dynamic changes of outcomes over time within each individual. However, when the number of outcomes is large, it becomes challenging and often infeasible to tackle the large covariance matrix of the random effects involved in the model. A high-dimensional response growth curve model, with three novel components, is proposed: a low-rank factor model structure that substantially reduces the number of parameters in the large covariance matrix, a re-parameterization formulation coupled with a sparsity penalty that selects important fixed and random effect terms, and a computational trick that turns the inversion of a large matrix into the inversion of a stack of small matrices and thus considerably speeds up the computation. An efficient expectation-maximization-type estimation algorithm is developed, and the competitive performance of the proposed method is demonstrated through both simulations and a longitudinal study of brain structural connectivity in association with human immunodeficiency virus.