Comparing Neural and Digital Circuits on Achieving Basic Functions Necessary for Data Processing

The purpose of this study is to elucidate the behavior of neural circuits. To do so, it is necessary to clarify the relationship between each neuron's inputs and outputs in order for neurons to connect in the circuit. In conventional synaptic integration theory, excitatory postsynaptic potentials (EPSPs) from multiple spines must occur almost simultaneously in order to add up them to generate an output. Thus, it is considered to be difficult for each neuron to establish synaptic integration by outputs of independent adjacent multiple neurons in the circuit. Recently, a theory that may provide a solution to this severe timing problem was proposed. The theory is that the Ca2+ ions retained in the spine for a long period of time polarize the neighboring highly dielectric spine-neck and dendritic fluid, resulting in an increase in membrane potential and the establishment of synaptic integration. In this study, I derived a conditional Equation for the establishment of synaptic integration that includes the effect of inhibitory neuron output, based on this theory. Based on this Equation and the morphology of neurons, I determined the circuit symbols and operation rules of neurons, and investigated to what extent a neural circuit consisting of excitatory and inhibitory neurons can reproduce the basic functions necessary for information processing compared to a digital circuit. The results showed that most of the basic functions necessary for information processing can be realized and that inhibitory neurons play important role, while there are some peculiarities as a neural circuit.