CS Memory-encoding Pathway LTP And Early Non-targeting LTP As Induced In The CA1 Hippocampus During Associative Learning

As a key brain area for learning and memory,the hippocampus is responsible for online acquisition,early storage and consolidation of memory.It is currently believed that the neural basis for the realization of learning and memory functions is the longterm potentiation of synaptic plasticity(long-term potentiation,LTP;long-term depression,LTD).Among them,LTP is the most popular and widely studied synaptic plasticity change model in the process of learning and memory.Previous research work mainly focused on the use of in vitro or extracellular electrophysiological recording methods to observe the changes in hippocampal synaptic plasticity after learning,and found that learning can induce changes in hippocampal neuron synaptic plasticity.A small number of studies have reported on synaptic plasticity activities in the learning process.The existing research results of this research group show that in the process of rewarding associative learning,the memory coding pathway(the CS coding pathway)produces LTP.The research work in this paper is further aimed at reward-associated learning,and explores the synaptic plasticity changes of hippocampal CA1 outside the memory coding pathway during the learning process,that is,the non-targeted neural pathway.The study found that: in the process of associative learning,the CS coding pathway in the hippocampal CA1 brain area produces LTP,that is,the synaptic response that encodes CS produces LTP.Interestingly,we measure the Schaffer collateral of the CA1 brain area by extracellular electrical stimulation./Associational Commissural pathway(hereinafter referred to as SC/AC pathway)(the stimulated SC/AC pathway and the combined stimulation pathway-including CS pathway and US pathway-do not overlap)synaptic connection strength,found: electrical stimulation of SC/AC The local field potential response induced by the pathway also produces significant LTP during the learning process.The SC/AC pathway is independent of the CS coding pathway in learning,and we also call it "non-targeted" neural pathways.Further analysis of the timing relationship between the LTP of the non-targeted pathway and the LTP of the CS coding pathway and the conditioned reflex behavior of experimental animals,it was unexpectedly found that the plasticity of the non-targeted pathway occurred earlier than the plasticity of the CS coding pathway,and it was also significantly earlier than the conditioned reflex.At the time point when the behavior is established,we call the LTP of the non-targeting pathway "early non-targeting LTP"(early non-targeting LTP).Immediately afterwards,we increased the difficulty of associative learning(changing CS,unchanged US),so that the experimental animals could not acquire memory during the training cycle.The results found that: CS memory coding pathway did not produce LTP,and significant LTP was still seen in the non-targeted pathway.Further comparison of early non-targeted LTP under different learning states showed that its occurrence time was completely different.The occurrence time of this LTP in the normal learning group Much earlier than the LTP of the unlearned group.The experimental results of this paper show the plasticity changes of different neural circuits in the associative learning process,and the discovery of the existence of early non-targeted LTP,which provides new research findings for understanding the synaptic plasticity mechanism of the hippocampal loop of associative learning and memory.