Behavioral tagging is one form of interactions between two independent memories in which short-term memory (STM) is transformed into a long-term memory (LTM) when the STM-training and another novel experience occur at short time interval. Previous studies showed that behavioral tagging resembles synaptic tagging in the interactions between short-term and long-term events, their requirement for de novo protein synthesis, and time windows between two events (~hours), suggesting that synaptic tagging mechanism may underlie the behavioral tagging. As a first step to clarify the involvement of synaptic tagging, we examined dynamics of cell ensembles that were activated during the formation of behavioral tagging. We set up a novel behavioral tagging paradigm using two different hippocampus-dependent memory tasks, novel object recognition (NOR) as a STM paradigm and novel place experience as a LTM paradigm, where NOR-STM was transformed into LTM by exposing mice to a novel place at a short interval of ~1h in a protein synthesis-dependent manner. Arc catFISH analysis identified cellular ensembles that were active during the behavioral tagging training. The number of neurons activated at both NOR and novel experience, denoted here overlapping neurons, increased in the CA1 region when the behavioral tagging was successfully achieved. Interestingly, there was no increase in the number of overlapping neurons in the CA3 and the DG regions, suggesting that inputs from two different information, NOR and novel experience, converged at the same neurons in the CA1 region. Together, our results suggest that synaptic tagging mechanism may be involved in the behavioral tagging.

Financial supports
JSPS KAKENHI grant number: 23220009
CREST, JST