Recent advances in 2-photon fluorescence lifetime imaging microscopy (2pFLIM) in combination with 2-
photon photochemistry have enabled the visualization of neuronal signaling during synaptic plasticity at the level of single
dendritic spines in light scattering tissue. Using these techniques, the activity of Ca2+/Calmodulin-dependent kinase II
(CaMKII) and Ras have been imaged in single spines during synaptic plasticity and associated spine enlargement. These
provide two contrasting examples of spatiotemporal regulation of spine signaling: Ras signaling is diffusive and spread
over ~10 μm along the dendrites, while CaMKII activation is restricted to the spine undergoing plasticity. In this review,
we will discuss the mechanisms and roles of the different spatiotemporal regulation of signaling in neurons, and the impact
of the spine structure upon these biochemical signaling processes.