Large data sets are becoming more common in fMRI and, with the advent of faster
pulse sequences, memory efficient strategies for data reduction via principal component
analysis (PCA) turn out to be extremely useful, especially for widely used approaches like
group independent component analysis (ICA). In this commentary, we discuss results and
limitations from a recent paper on the topic and attempt to provide a more complete
perspective on available approaches as well as discussing various issues to consider
related to large group PCA for group ICA. We also provide an analysis of computation time,
memory use, and number of dataloads for a variety of approaches under multiple scenarios
of small and extremely large data sets.