While odours appear to be rather simple sensory stimuli, it is as of yet unknown how the olfactory code operates: how is an olfactory image synthesized from the structural groups of the odour molecule that are recognized by the odorant receptors? Our lab is interested in the microcircuitry of the olfactory bulb that processes olfactory sensory information, in particular the role of granule cells. These inhibitory neurons represent the most numerous cell type in the bulb and interact with the principal neurons, the mitral cells, via dendrodendritic reciprocal synapses. We use two-photon laser scan microscopy in conjunction with whole-cell patch clamp recordings from individual neurons in acute brain slices to study calcium signals and correlated electrical activity in response to sensory-like input from mitral cells. These techniques allow us to optically detect synaptic activity at the level of individual synapses, that are located in large granule cell spines (see on the left).