The mushroom bodies are key features of the brain circuitry for insect associative learning, especially when evoked by olfactory cues. Mushroom bodies are also notable for the close-packed parallel architecture of their many intrinsic neuronal elements, known as Kenyon cells. Here, we report that Kenyon cells of adult Drosophila exhibit synchronous oscillation of intracellular calcium concentration, with a mean period of approximately 4 min. Robust oscillation within a dissected brain persists for hours in insect saline and is strongly modulated in amplitude by the product(s) of the memory consolidation gene, amnesiac. It is also sensitive to pharmacological agents specific for several classes of ion channel and for acetylcholine and GABA receptors. A role in memory consolidation involving transcriptionally mediated synaptic strengthening is proposed.