-From the insect brain to the bio-mechanic system-
To understand the mechanism of the brain is one of the most important project in the 21st century. We aim to understand the brain by analyzing biologically the structure and function of the brain and reconstructing the result by an engineering approach. However, analyzing each element of human's brain is very difficult due the enormous number of cells, no less than 10 billion neurons, which compose the cerebral structure. We therefore focus on the insect’s brain which consists of about only 100,000 neurons, as a model of a simple nerve system of the invertebrate. Although the nervous system of these animals is small, they are similar to us in some abilities. Their abilities range from athletic abilities like running, swimming, flying to memory learning or highly developed society as viewed in honeybees. Moreover, the way of identifying odors of insects is the same as the mammals. The change of neural circuit by the memory and learning was first manifested in aplysia, and it is widely used as a model of neural circuit research.
We perform our research in many ways, from single cells of the neural system to the actual behavior. To record the neuron activity, we perform intracellular recording with a micro-glass electrode, or a high-speed voltage-sensitive dye/ Ca imaging to capture a single cell or regional activity in the brain. To observe the actual behavior, we use treadmill, servo-sphere, or high-speed camera. We revealed that Bombyx males can orient toward the odor source without using complex memory and learning but by simply repeating the set and reset of the programmed behavior, and estimated the neural circuit of the bombyx's odor searching behavior. To examine the circuit, we reconstruct the realistic large-scale neural network model and simulate the model using the next generation supercomputer. The abstracted model was also implemented into a insect-size mobile robot. This robot could reach the odor source.
The behavioral strategies based on the neural mechanisms were evaluated by the insect-size robot and we have revealed that Bombyx males can turn toward the odor source without using complex memory and learning but by simply repeating the set and reset of the programmed behavior caused by a complex distribution of odors in the air. Our interdisciplinary research between biology and engineering has been highly esteemed.
Moreover, we do not only think the insect brain as a model in the brain research. As could be seen in fossils of arboniferous period more than 3 billion years ago, insects still exist without changing their structure despite many environmental changes. This is the result of their architecture, highly adaptive to the environment, and it also draws attention from robotics. We aim to make a bio-mechanical hybrid system, a system with an insect integrated in a robot, which is driven from the insect's neural signals. By operating the system in many environments, we hope to make a real-time observation of neural activity adapting to the environment and changing every second, and learn their architecture which is prominent in environmental adaptability.
Recently, we've succeded in expressing channel rhodopsin2 onto a pheromone receptor cells of a male silkmoth. This success made it possible to activate the olfactory receptor cells with light stimulation instead of odorant. We can control the number of spike generataion on the olfactory receptor cells.
Our approaches at different levels are strong to reveal the complex brain system.
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