Fig. 1. Scales of functional architecture accessible to fMRI in humans and to optical imaging in animal models.

Although continued technological development has decreased the spatial resolution of human fMRI to the submillimeter scale, further developments will be required to resolve units of cortical functional architecture such as cortical columns and layers over the entire brain. At the same time, invasive optical imaging techniques have expanded their spatial coverage to several millimeters, and in some cases an image plane covering a slice of the entire two cerebral hemispheres. Recent studies have shown that as these two complementary imaging modalities converge they can inform one another, yielding new insights into brain function. Further technological advances are required to continue to enhance the spatial resolution and neuronal specificity of human fMRI while retaining whole-brain coverage.