CRIS -Creative Research Institution- Hokkaido University

【Division of Innovative Research】Toshiyuki NAKAGAKI

Toshiyuki NAKAGAKI Non-Traditional Science
Intelligent calculation method learned from the mysterious amoeba in slime molds -an example in network design-
Toshiyuki NAKAGAKIAssociate Professor (Doctor of Philosophy)

Learning from an amoeba

The following is a press release from NATURE magazine: "Pieces of the slime mold Physarum polycephalum placed in a 3-centimeter-square maze join up and expand to fill all available space. But when two pieces of food are placed at separated exit points in the labyrinth, the organism withdraws itself from dead ends until its entire 'body' runs between the two nutrients along the shortest possible route (Fig. 1). Effectively, it solves the puzzle. 'This remarkable process of cellular computation implies that cellular materials can show a primitive intelligence', the researchers say."

 

Amazing in a maze

 The following is a press release from NATURE magazine: "Pieces of the slime mold Physarum polycephalum placed in a 3-centimeter-square maze join up and expand to fill all available space. But when two pieces of food are placed at separated exit points in the labyrinth, the organism withdraws itself form from dead ends until its entire 'body' runs between the two nutrients along the shortest possible route (Fig. 1). Effectively, it solves the puzzle. 'This remarkable process of cellular computation implies that cellular materials can show a primitive intelligence', the researchers say."

 

Smartness of transportation network among nutrients

 Figure 2 shows the extending organism on the agar surface where many nutrients (black dots) are distributed. Thick tubes connect the nutrients, and the connection route shows a geometric shape. The body of the plasmodium contains the network of tubular elements by means of which nutrients and chemical signals circulate through the organism in an effective manner. Circulation is based on streaming through a complicated network of tubular channels. Thus, the geometry of the channel network is related to the exchange of chemicals within the organism. Since the tubes disassemble and reassemble within a period of a few hours in response to external conditions, this organism is very useful for studying the function and dynamics of natural adaptive networks. So we try to evaluate the smartness of the network shape in terms of the recently growing idea of a so-called 'small-world network'.

 

Dynamic design of the network

How does the organism obtain the smart solution? Two empirical rules describing changes in body shape are known: 1) tubes of open ends are likely to disappear in the first step, and 2) when two or more tubes connect the same two food sources, the longer tubes tend to disappear. These changes in the tubular structure of the plasmodium are closely related to the spatio-temporal dynamics of cellular rhythms. Shuttle streaming of protoplasm, which is driven by hydrostatic pressure induced by rhythmic contraction, may affect the morphogenesis of tubular structures. Hence, a key mechanism underlying network formation may involve the spatio-temporal dynamics of oscillatory fields with complex shapes and moving boundaries. Then we try to make mathematical model for the morphogenesis, and to clarify the plasmodium's way of computing.