A key goal in functional neuroimaging is to track the neuronal correlates of mental activity based on signals related to local changes in metabolism and blood flow. Recent findings indicate that the dendritic processing of excitatory synaptic inputs correlates more closely than the generation of spikes with the brain imaging signals. The correlation is often non-linear and context-sensitive, and cannot be generalized for every condition or brain region. The vascular signals are mainly produced by rises in intracellular calcium in neurons and possibly astrocytes, which activate key enzymes that produce vasodilators to generate increments in flow and, in turn, the positive BOLD (blood-oxygen-level-dependent) signal. Our new knowledge of the cellular mechanisms of functional brain imaging signals place constraints on the interpretation of the data.
