Hippocampal Functional Organization in Fear Memory

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It is well known that the entorhinal cortex (EC) is one of the main sources of inputs to the hippocampus necessary for the formation of episodic memory. However, how multimodal factors in episodic memory are processed in the EC is not well understood. In the present study, we investigated individual EC sub-regional contributions in episodic memory to determine a possible functional dissociation of EC sub-regions. We fear conditioned animals on a plus maze with two different types of stimuli - spatial or object, which is processed in MEC and LEC, while optogenetically inhibiting MEC/LEC. I finished behavioral experiments and statistically analyzed behavioral and histological data.In weak foot-shock condition (0.3mA), LEC inhibited animals (n=6) showed significantly lower avoidance toward shocked object than control animals (n=7; p < 0.005). Avoidance toward the shocked arm of MEC inhibited animals (n=8) was also comparatively lower than controls (n=7; p = 0.06). In strong foot-shock condition (1mA), LEC inhibited (n=6) as well as control (n=8) animals showed over 90% avoidance toward shock object, however, LEC inhibited animals avoided not only the shocked but also no-shocked object significantly longer than controls (p < 0.05). In place fear conditioning, MEC inhibited animals (n=7) tended to avoid the no-shocked arm, which is adjacent to the shocked arm, longer than control animals (n=4; p = 0.07). These results suggest that EC sub-regions process information about specific place/object as well as associate the information with fear memory.