Chemical basis for minimal cognition

Martin Hanczyc, Takashi Ikegami

Publikation: Konferencebidrag uden forlag/tidsskriftPaperForskningpeer review


We have developed a simple chemical system capable of
self-movement in order to study the chemical-molecular
origins of movement, perception and cognition. The system
consists simply of an oil droplet in an aqueous environment.
The aqueous phase contains a surfactant that
modulates the interfacial tension between the drop of oil
and its environment. We embed a chemical reaction in
the oil phase that reacts with water when an oily precursor
comes in contact with the water phase at the liquidliquid
interface. This reaction not only powers the droplet
to move in the aqueous phase but also allows for sustained
movement. The direction of the movement is governed by
a self-generated pH gradient that surrounds the droplet.
In addition this self-generated gradient can be overridden
by an externally imposed pH gradient, and therefore the
direction of droplet motion may be controlled. Also we
noticed that convection flow is generated inside the oil
droplet to cause the movement, which was also confirmed
by simulating the fluid dynamics integrated with chemical
reactions (Matsuno et al., 2007, ACAL 07, Springer,
p.179, Springer). We can observe that the droplet senses
the gradient in the environment (either internally generated
or externally imposed) and moves predictably within
the gradient as a form of primitive chemotaxis (Hanczyc,
M., et al., 2007, J. Am. Chem. Soc., 129, p. 9386).
By creating a pH gradient and concomitant convection
flow, the droplet behaves as if it can perceive the environment.
We believe that the geometry of the interface
shape can control sensitivity to the environment (Ikegami
et al., 2008, BioSys., 91, p.388). This geometry-induced
fluctuation is the source of fluctuation of motion, which
we think is tightly linked with the idea of biological autonomy.
There is empirical evidence to support the above
ideas. Some form of internal bias is necessary for breaking
symmetry to cause self-movement and the bias may be
the result of perception of the environment.
Such simple oil droplet systems show autonomy in
the sense that the droplets move in response to the selfgenerated
pH and the environmental gradient. In our
modeling, we demonstrated that a computational autopoietic
cell could move by continuously self-repairing the
membrane, but in this case failed to show any gradientclimbing
behavior (Suzuki et al., 2008, Artificial Life, in
press). This may be due to the fact that the autopoietic cell
can only survive in the narrow range of environments that
support a certain substrate density. Compared with that
autopoietic cell model, our oil droplets are more stable and
they strive to maintain their boundary structures. We hypothesize
that the pH gradient around the droplet results
in an unbalanced interfacial tension at the interface. The
droplet then responds by motion in order to maintain a balanced
interfacial tension. Once the tension forces around
the droplet are balanced the droplet would stop moving.
In this way, we contend that a kind of homeostasis is a basis
for self-movement. Different from the mere physicalchemical
process, any life system preserves its own identity
and consistency with respect to the environment. This
homeostasis, rooted on the sensory motor couplings, will
organize minimal cognition (see also, Ikegami , T. et al.,
2008, BioSys., 91, p.388 ]
StatusUdgivet - 2010
BegivenhedALife IX - Winchester, Storbritannien
Varighed: 4. aug. 20088. aug. 2008


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