To determine the relationship between synaptic structural changes and cortical function, we recently published a study where we imaged dendritic spines using two-photon in vivo microscopy while monitoring network activity in the visual cortex using intrinsic signal imaging. By manipulating cortical activity levels by dark-rearing mice and re-exposing them to light, we found a close inverse correspondence between dendritic spine structural dynamics and visually evoked cortical function on a timescale of days. Light exposure following dark-rearing slowly increased visually evoked cortical processing and stabilized dendritic spine structure, an effect partially mimicked by diazepam injections in dark reared mice suggesting that this slow recovery is mediated by inhibitory signaling. Surprisingly, very brief (2 h) periods of light exposure led to an NMDA-dependent rapid reorganization of cortical networks with an early emergence of visually-evoked cortical activation and enhanced spine dynamics. Here we further explore the relationship between spine morphology and visual function.