The hippocampus plays a central role in learning and memory to process and associate multimodal sensory and episodic information [
1]. Previous studies showed that the
N-methyl-
d-aspartate receptors (NRs) that express broadly in the central nervous system are crucial for regulation of excitatory synaptic transmission, synaptic plasticity, and some forms of cognitive functions [
2]. NRs in dentate gyrus (DG) are involved in pattern separation [
3] and NRs in CA3 are involved in the reverberatory association of sensory inputs [
4] and pattern completion [
5]. NRs in CA1 are involved in the memory acquisition [
6], indicating that NRs in the hippocampus are essential for multiple brain functions. Within the DG-CA3-CA1 trisynaptic circuit of hippocampus, the CA3 forms extensive interconnections within CA3, that is called as a recurrent circuit [
7] where NRs are required for excitatory transmission and long-term potentiation (LTP) among CA3-CA3 synapses. Theoretical models have suggested that the CA3 recurrent circuit implemented with NR function is capable of preserving multiple information to generate a new associative memory [
8,
9]. This implies that the simultaneous and artificial reactivation of specific cell ensembles in CA3 corresponding to pre-stored distinct memories enables to induce the artificial association that is a new link between distinct memories and an acquisition of a new memory. To test this possibility, we have established the optogenetic technique to specifically manipulate CA3 ensemble corresponding to the behavioral event [
10,
11]. We showed that activation of CA3 ensemble recalls the memory [
11] and that synchronous activation of distinct cell populations in CA3, which correspond to distinct events links these initially independent events [
10]. These findings suggest that the CA3 recurrent circuit expressing NRs mediates artificial association of memory events stored in CA3 ensembles. However, it is still unclear whether CA3 NRs are crucial for the artificial association of memory events stored in the CA3 ensembles. In this study, we aim to clarify the role of CA3 NRs in the artificial association, which would provide an important insight into the hippocampal CA3 recurrent circuit in learning and memory.