The BOLD plot thickens: sign- and layer-dependent hemodynamic changes with activation.

In this issue of Neuron, Goense et al. (2012) report on high-resolution, layer-specific measurements of BOLD, cerebral blood volume, and cerebral blood flow in regions of positive and negative BOLD associated with a simple visual stimulus. The findings strongly suggest that the hemodynamic mechanisms behind negative signal changes are quite different from those behind positive signal changes.