Study On Mechanism Of Excitation-inhibition Balance And Firing Rate Homeostasis Through Synaptic Plasticity

Cortical neurons receive excitatory and inhibitory synaptic currents. Balance of the two opposing sides is the basis for maintaining stability and information processing of cortical cortex. Firing rate homeostasis is an ubiquitous phenomenon in cortical circuits, and it is important for integrating, adjusting, transferring information. Extensive experimental researches have demonstrated that synaptic plasticity plays a crucial role in maintaining the excitation-inhibition balance and the firing rate homeostasis. However, the underlined mechanism remains unclear. On the context, the research aims to elucidate the mechanism underlined balance between excitation and inhibition and the firing rate homeostasis.Firstly, a feedback neural circuit model is constructed. It is mainly composed of an excitatory and inhibitory feedback loops and a feed-forward loop. Furthermore, the STDP-type synaptic plasticity is incorporated into this model. The neural circuit model is implemented using Leaky Integrate-and-Fire(LIF) neural model, and parameter values of the model were determined by the anatomical data.Secondly, the feedback neural circuit model was used to study the balance between excitatory and inhibitory underlined by synaptic plasticity. We analyzed the excitation-inhibition balance of the excitatory and the inhibitory neural circuit using the following approaches, respectively: scatter diagram of inhibitory and excitatory current, the plot of ratio of excitatory current to inhibitory current. The results demonstrated that excitatory and inhibitory synaptic currents can achieve precise balance under the regulation of synaptic plasticity. Moreover, we studied the robustness of the balance between excitatory and inhibitory. The results show that the neuron can maintain the balance even in the presence of input disturbances and parameter perturbations. The results indicated that neuronal excitability-inhibitory balance has strong robustness. Finally, we provide a simple explain for the mechanism of the balance between excitatory and inhibitory synaptic currents underlined by synaptic plasticity.Thirdly, firing rate homeostasis of the feedback neural circuit was researched. We analyzed the firing rate homeostasis of the feedback neural circuit using neuronal membrane potential and the statistics of the firing rate. The results indicate that the firing rate is equal to the desired neurons firing rate, which show that the model can achieve firing rate homeostasis under the regulation of STDP-type synaptic plasticity. Furthermore, we studied the robustness of neuronal firing rate homeostasis. The results indicate that the neuron can maintain the firing rate homeostasis even in the presence of input disturbances and parameter perturbations. We further analyzed the mechanism of firing rate homeostasis underlined by synaptic plasticity, which provides an explanation for and insight into why and how the model can achieve the perfect firing rate homeostasis. Finally, relationship between excitability-inhibitory balance and firing rate homeostasis is elucidated, which reveals that the balance and homestasis are the two sides of the same coin.In the discussion section, we incorporated simultaneously excitatory and inhibitory synaptic plasticity into the neural feedback model, the results illustrate that the neuron can achieve the balance and the firing rate homeostasis on the condition that the inhibitory learning rate is greater than the excitatory learning rate. Otherwise the balance and the firing rate homeostasis will be lost. Moreover, excitability-inhibition balance and firing rate homeostasis can be improved by increasing the number of neuron in feedback circuit. Additionally, parameter values of synaptic plasticity have a significant impact on dynamic response speed of excitatory-inhibitory balance and firing rate homeostasis.This research results illuminate that the synaptic plasticity plays a crucial role in achieving and maintaining both excitatory-inhibitory balance and firing rate homeostasis. Since excitatory-inhibitory balance and firing rate homeostasis are the core scientific issues in the field of neuroscience, the research results of this study will shed light on and provide guideline for the further research of excitatory-inhibitory balance and firing rate homeostasis.