Voltage-sensitive dyes can be used to image cortical network function with millisecond temporal resolution and with a horizontal spatial resolution of approximately 50 µm. This imaging technique can be combined with whole-cell patch-clamp measurement of membrane potential followed by the anatomical analysis of neuronal morphology. Together, such experiments reveal the relationship of activity recorded in individual identified neurons with the spatiotemporally resolved ensemble dynamics of a cortical region. Application of these techniques to the rodent barrel cortex has advanced our understanding of the synaptic mechanisms underlying sensory responses to simple whisker stimuli.