There are a few limitations of present study, which need to be addressed in future layer-specific fMRI functional connectivity related research. First, different methods exist for identifying different cortical lamina from MRI data. The method we employed was to construct laminar profiles, which keeps a relatively fixed distance to the cortical boundaries (Fig. 1), the so-called equidistant laminae [18, 72, 73]. An alternate approach is the equipotentials method, wherein the equipotentials are computed between the inner white matter surface and pial surface with the Laplace equation, and then the cortical profiles can be constructed along the gradients [74]. However, the drawback with this approach is that the Laplacian equation may not match the anatomical layers observed from high-resolution MRI [75]. Recently a new model called equal-volume model for identifying cortical laminae was proposed by Waehnert et al. [75], and they claimed that it provides a better fit to observed cortical layering. In future, studies must compare the three different models for how well functional connectivity derived from layers constructed by them match the underlying anatomical predictions.
