A central tenet of cortical operations is that excitation and inhibition rise in tandem through out a column, and over the somatic and dendritic compartments of single neurons. The details of how excitation flows in a column, how inhibition arises in different lamina to balance excitation, and how excitation and inhibition interact along the dendrite of pyramidal neurons – especially in vivo -- are not known. Our specific aims are to measure activity in all lamina of cortex, to measure activity of interneurons in all layers, and to directly measure the effect of inputs, activity, and behavioral state on dendritic activation and somatic output of interneurons and layer V pyramidal neurons. We will deploy 2-photon imaging methods for measuring state dependent changes in activity in layers 1-6, of somatosensory forepaw and barrel cortex, from known classes of neurons, and from the soma and dendrites of layer V pyramidal neurons in awake behaving, and anesthetized animals. The guiding hypothesis of this proposal is that excitation will be matched by inhibition in all cortical lamina, and during all states. A second simple hypothesis that is that inputs to apical dendrites will be amplified in all layer V neurons that fire action potentials. We will test these hypothesis during spontaneous activity, sensory stimulation and behavior. These studies will provide fundamental insights into cortical function.