Calcium release from intracellular stores has various actions in neurons, but its effects on network oscillation have not been well understood. The olfactory center (procerebrum, PC) of the terrestrial slug Limax valentianus shows a regular oscillation in the local field potential (LFP). Here we report that caffeine, which is an agonist for ryanodine receptors and triggers calcium release from intra-cellular stores, has strong modulatory effects on the PC. In isolated PC neurons, caffeine enhanced the cytoplasmic calcium concentration, and this was blocked by ryanodine. Caffeine elevated the frequency and amplitude of the LFP oscillation, which was also blocked by ryanodine. The time lag between the frequency and amplitude effects suggests distinct mechanisms for the modulation of these two parameters. These results suggest that calcium release from intracellular stores through ryanodine receptors activates network activity in the PC.