Coding Analysis Of Innate Defensive Behaviors In Mice BLA And DPAG Nuclei Under Fear Visual Stimuli

Making appropriate defensive behaviors to deal with various potential threats is a vital guarantee for animals to obtain survival and reproduction opportunities.Flight and freezing are the two major defensive behaviors in the process of avoiding natural enemies in mice.When they are exposed to innate threats,visual cues are processed and transmitted by the visual system into the emotional nuclei,and finally transmitted to the periaqueductal gray to make the body produce defensive behaviors.The basolateral amygdala(BLA)and dorsal periaqueductal gray(dPAG)play important roles in the regulation of innate defense behaviors,but the roles of two nuclei and how they encoding different defensive behaviors is unclear.Therefore,in order to reveal the neural mechanism of BLA and dPAG encoding different defense behaviors,C57BL/6 mice were used as experimental subjects for research in this paper.The research results will help us to have a deeper understanding of the generation and regulation mechanism of defensive behavior,and deepen the research on the self-protection mechanism of the brain.We use the Looming and Sweeping visual stimuli to simulate predators from the sky to induce innate defensive behaviors in mice,and simultaneously acquired neural activity signals in the BLA and dPAG brain regions.Extracellular action potential(Spike)and local field potential(LFP)signals were extracted from the raw signals.In this paper,the coding analysis is carried out from the perspectives of the firing rate and firing interval characteristics of the Spike signal,the frequency band activity and network connection characteristics of the LFP signal,etc.,and use Support Vector Machine(SVM)and Decision Tree algorithm to decode and verify the above encoding features.The specific work and research results are as follows:(1)First,the experimental scheme was designed and the platform was built.Then the multi-array electrodes were implanted into the BLA or dPAG brain regions of six mice,and the neurophysiological signals of the mice under defensive behavior were collected.Signals were preprocessed,data screening was done,and a statistical analysis of the defense responses of mice to visual stimuli was performed.The results showed that the SNR of signal was significantly improved after pretreatment,which can improve the reliability of the analysis results;Looming and Sweeping visual stimuli could effectively induce the flight and freeze behavioral responses in mice.(2)Spike signals in BLA and dPAG brain regions under two defense behaviors were analyzed from the perspective of Spike firing rate and firing interval.The results showed that spike firing rates in both brain regions were significantly increased during flight and significantly decreased during freezing.The differences in the distribution of ISI intervals between the two brain regions were mainly within 2-10 ms under flight and freeze behaviors.The two brain regions have high consistency in the Spike characteristics of the two defense behaviors,and the frequency and firing interval of neuron activity have obvious correlations with the choice of defense behaviors.(3)Morlet wavelet was used for time-frequency analysis of LFP signals in BLA and dPAG regions.The results showed that the neural activities of the two regions under the flight and freeze were mainly concentrated in the theta band,and the flight behavior was mainly at 8-10 Hz,while the freezing behavior was mainly at 6-8 Hz.The frequency oscillations of the two regions are highly similar.Then,the synchronicity of theta and gamma band between each channel was calculated by using the SL algorithm and the brain functional network was constructed.The changes of connectivity and topological properties of the network showed that the network connection density of theta band was significantly enhanced under the flight and freezing behaviors,and the neurons showed high synchronization in the theta frequency band.(4)The Spike and LFP features were verified using SVM and Decision Tree algorithms.The results show that the accuracy of the two algorithms for single feature is about 80%,and some features are more than 85%;and the accuracy of the combined feature is better than single feature.The results show that the coding features extracted in this paper can effectively characterize two defense behaviors.It also indicates that both the BLA and dPAG nuclei are involved in the regulation of the flight and freeze behaviors,and there are obvious differences in the neural coding patterns and coding characteristics between the two innnte defense behaviors.