The negative BOLD signal unmasked.

Many fMRI experiments show regions of cortex that seem to respond in antiphase with the primary stimulus. In this issue of Neuron, Shmuel et al. show that this "negative BOLD response" is spatially and temporally linked to reductions in blood flow. By combining BOLD and blood flow data to model the energy consumption in cortex, they conclude that the NBR is primarily due to active neuronal inhibition.