Estimation of the neural circuit for the command generation in the premotor center of an insect brain

We report an approach to estimate the functional connection from the possible anatomical connections and physiological response of each neuron. Here we focus on the brain of Bombyx mori, a male silkmoth, which exhibits a programmed behavior for the pheromone orientation on a pheromone detection. The neuroethological experiments revealed that the motor command is generated in the premotor center, composed of the lateral accessory lobe (LAL) and the ventral protocerebrum (VPC). The morphology and the physiological response to the pheromone stimulus are obtained for each main type of LAL-VPC neuron through the intensive electro-physiological and immunohistochemical experiments. However, how the motor command is generated in LAL-VPC, or the information pathway in the network, is still unknown. That is, each piece of puzzle is fairly well investigated, though they are not yet fit in to reveal the whole picture. The goal of our present study is to investigate the functional connection in LAL-VPC to elucidate the mechanism of the motor command generation for the programmed behavior. The present approach is to consider an artificial three-layered neural network to solve an optimization problem based on the above findings of LAL-VPC neuron as the constraints. The optimal solution is the connection which reproduces the observed response best, and we search it through the learning of the artificial neural network. Then, the obtained connection is evaluated by a simulation of LAL-VPC network to reproduce the network dynamics.