they are more sensitive to larger vessels [51]. However, a recent investigation of the spatial point spread function (PSF) for the BOLD response showed that the laminar PSF of the gradient-echo BOLD signal had a “flat-tail” characteristic across layers, with the tail running to the pial surface [52]. This indicates that lower layers contribute signal to any given layer in gradient-echo BOLD. While spin echo BOLD may provide better spatial laminar specificity, one may lose sensitivity to the BOLD effect when using spin echo. Investigations into the laminar specificity of BOLD as well as HRF variability across cortical layers have invariably used task-based paradigms and cannot be readily generalized to resting state given that neurovascular coupling likely operates under a different regime in resting state (see extension of Buxton’s balloon model to resting state conditions [53].
