studies at the laminar level, even with the loss of sensitivity in spin echo compared to gradient echo. Recently, an extension of the Friston–Buxton hemodynamic model, which accounts for blood draining effects by coupling local hemodynamics across layers in dynamic causal models of fMRI during visual activation, was reported [14]. However, priors about two parameters controlling blood draining effects (the delay τd between the lower and upper layers, and λd which represents the strength of the blood draining effect from the lower to the upper layers) need further experimental validation in human resting state studies. Investigations into the laminar specificity of BOLD 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]. Therefore, further modeling and experimental work is needed in this area, which could potentially lead us to a reliable and accurate laminar time series that will allow a more fine-grained investigation of resting state FC at the laminar level.
