Plant-derived flavonoids have been demonstrated to enhance cognitive function in various organisms, including invertebrates. In the pond snail Lymnaea stagnalis, epicatechin facilitates memory formation through conditioned taste aversion (CTA) training. These snails were categorized into two groups: "good learner" and "poor learner", based on their feeding behaviour 24hours after CTA training. The "good learner" snails showed at least a 40% reduction in feeding behaviour compared to the pre-test levels, while the others were categorized as "poor learner". This study first investigated the effects of low doses of epicatechin on long-term memory (LTM) formation in snails. The results revealed significant memory retention only in 'good learner' snails treated with 1.5mg/L epicatechin, demonstrating their superior learning ability. Mianserin, a serotonin antagonist, blocked the enhancement of LTM formation, typically lasting over 72hours after epicatechin (15mg/L) treatment. Conversely, the mianserin-only group exhibited memory retention levels similar to those of the control group. These findings suggest that serotonergic cerebral giant cells (CGCs) are necessary for epicatechin to promote LTM formation following CTA training. To investigate the CGCs' spontaneous activity in snails exposed to epicatechin, a local field potential (LFP) measurement method was developed. This method recorded the activity of CGCs and their surrounding neurons. Administration of 1mM GABA to "poor learner" snails reduced LFP spike activity around the CGCs, while having no significant effect on LFP spike activity in "good learner" snails. These results suggest that serotonergic and GABAergic systems play crucial roles in epicatechin-mediated enhancement for CTA-LTM in snails.Figure1. intracellular and extracellular measurements.