The Mechanisms Of Hippocampal CA2-CA1 Rhythms Involved In Encoding And Retrieval Social Memory

Social behavior refers to the activities in which individuals engage in physical and mental exchanges in social environment.It includes social cognition activities and social memory.The hippocampus,a brain region related to cognition and memory,plays an equally important role in social interaction.Existing studies have revealed the important role of hippocampal CA2 area in social activities and social memory from the aspects of anatomy and neuron spiking activity.Research of neural circuit shows that in addition to the classic CA3-CA1 pathway,there is also a CA2-CA1 neural pathway in the hippocampus,which provides a physiological basis for the transmission and integration of social information in the two brain regions.The transmission and integration of information in the hippocampus depends on the synchronized electrical activity of neuronal clusters,and this electrophysiological activity is manifested at the mesoscopic level as periodic neural rhythms.There are mainly following types of rhythms in the hippocampus: theta(4-12 Hz),slow gamma(25-55 Hz),fast gamma(65-100 Hz),and Sharp-wave ripples(SWRs,0.01-3 Hz sharp waves superimposed on ripples of 150-300 Hz).Studies have shown that hippocampal CA2 area is involved in the generation of slow gamma rhythm and SWRs rhythm,and activating CA2 area neurons in a social environment can enhance slow gamma rhythm in CA1 area;SWRs in CA2 area contributes to the consolidation of social memory during slow wave sleep.This indicates that slow gamma in hippocampal CA2 area can participate in the encoding of social activities through the CA2-CA1 pathway;after the end of the social task,SWRs in the resting state and the slow gamma in the exercise state may participate in the retrieval of social memory.Therefore,the purpose of this study was to investigate the mechanisms by which neural rhythms in hippocampal CA2 area as well as CA2-CA1 pathway are involved in social behavior encoding and social memory retrieval.we analyzed the mechanisms of hippocampal CA2 area and CA2-CA1 pathway rhythms involved in the encoding of social activities and retrieval of social memories by recording the behaviors of rats in social experiments and the local field potential(LFP)in the hippocampus.The main results of this study are as follows.1.Slow gamma power in hippocampal CA2 in social activity states was significantly higher than that in non-social state.2.The unidirectional transmission of slow gamma rhythm in the hippocampal CA2-CA1 pathway is significant in the social activity state,and the Directional Index(DI)of information flow is higher than that in the non-social state.3.The rates of SWRs in hippocampal CA1 area increased significantly after the end of the social task in awake resting state.Compared with non-social conditions,when the rats returned to the original open field again after the social task,slow gamma power in hippocampal CA1 area increased significantly.Based on the above results,the main conclusions of this thesis are: 1.hippocampal CA2 slow gamma rhythms are involved in the encoding of social activities.2.hippocampal slow gamma rhythms transmit and integrate social information through the CA2-CA1 pathway.3.hippocampal CA1 slow gamma and SWRs are involved in the retrieval of social memory.In summary,this study investigates the mechanisms of hippocampal CA2-CA1 network involved in social function,providing new ideas for early detection and non-invasive detection of mental disorders characterized by social disorders,as well as providing theoretical basis and experimental support for the diagnosis and treatment of this type of disorders.