In the mammalian olfactory bulb, granule cells (GCs) mediate self- and lateral inhibitory interactions between mitral/tufted cells via a dendrodendritic reciprocal synapse. Although axonless, GCs spike during odorant stimulation. Using two-photon imaging in acute rat brain slices and sensory-like stimulation, i.e. extracellular activation of a glomerulus, we observed a prolonged depolarization following the spike that is correlated to substantial Ca²⁺ influx throughout the dendrite (n = 34 cells). These effects are significantly different from what is observed when the GC spike is evoked by current injection. The plateau potential depends on NMDA receptor activation and the non-specific cation current I_can . A possible link to TRP channels is currently under investigation. In coincidentally activated spines, local and global Ca²⁺ signals summate (n = 10 spines), possibly endowing GCs with sub- and suprathreshold associative plasticity. The long-lasting signal may contribute to the asynchronous release from GCs that governs the slow timecourse of lateral inhibition between olfactory bulb mitral cells.