“These models demonstrate the combined influence of sensory input and memories on brain activity,” Ermentrout said. “Brains convert sensory information into action. If a ball is thrown at you, you duck or catch it because you know that the ball could hit you. That knowledge and the sight of the ball coming at you dictate your action. A mollusk collects sensory information from its previous pigmentation and converts it into motor action by producing more pigmentation and continuing the pattern.”
(above) — from Pitt, Berkeley researchers reconstruct seashells to model nervous system function (Apr 9, 2009) from FirstScience News
Starting from a slender, tapered shard, the shell of the Conus gloriamaris grows gradually outward in a lazy spiral, flaring out as it wraps itself in layer after layer of gleaming tan-and-white marbling. The meticulous design of a seashell has long been a source of fascination for mathematicians, but the biological process involved has remained mysterious. Equipped with a new understanding of how mollusks use an extensive network of nerve cells to coordinate precise deposits of shell material and pigment, researchers can now simulate the growth of almost any seashell on a computer. And while this may delight molluscophiles, the significance is broad: This advance marks a triumphant cross-pollination between mathematics and biology that is also yielding important insights into how complex neural networks interact and communicate.
… recent findings suggesting that the mantle uses pigment patterns in the shell as a “diary” of past shell-building activity. During shell construction, the mantle is always extended just a bit beyond the lip of the shell, inspecting its prior handiwork; [George] Oster and [Bard] Ermentrout hypothesized that pigment patterns from days past are scanned and interpreted by the mantle’s nerve network, triggering waves of excitation and inhibition that yield detailed instructions for the next round of construction. “What the mantle is doing is ‘tasting’ back in time,” says Oster, “so it can predict what it should do the next day and so that the pattern will be continuous.”
… the primitive form of “memory” observed in mollusk neural networks might help researchers to decipher how far more sophisticated networks in the human brain enable us to use prior experience to build a picture of our world. To deepen their understanding, the team is now turning their attention to the cuttlefish, which rapidly changes colors and patterns.. “The patterns are very dynamic, and instead of taking months to form, they do it in a millisecond,” Oster says, “but it’s the same kind of nervous net, and it’s working in very much the same way.”
(above) — from What Seashells Tell by Michael Eisenstein (May 8, 2009) from Seed magazine
The “neural net” model explains how mollusks build their seashells based on the finding that the mollusk’s tongue-like mantle, which overlaps the edge of the growing shell, senses or “tastes” the calcium carbonate layer laid down the day before in order to generate a new layer.
“The pattern on a seashell is the mollusk’s memories,” said Oster, a professor of environmental science, policy and management and of molecular and cell biology. “The shell is laid down in layers, so the mantle is sensing the history of the mollusk’s ‘thoughts’ and extrapolating to the next layer, just like our brains project into the future.”
… “Our real contribution is not reproducing the patterns, but showing that the nervous system can do it with one equation based on the principle discovered by Ernst Mach in the 1860s,” Oster said.
… Ironically, most sea snails don’t care a whit about their shell pattern. They are buried in the mud of the seafloor where their patterns are hidden even from potential mates.
“The pigment is a cue to get the mantle in register so it builds the right shaped shell, and is only an epiphenomenon reflecting neural activity,” Oster said. “It is incidental to the snail.”
“There is no strong selective pressure to drive patterns, so evolution can explore the entire parameter space” of possible shells, Boettiger added. “That was one rewarding thing about this work; it brought some nice aesthetics to the whole project.”
(above) — from Sea mollusks taste their memories to build shells by Robert Sanders (Apr 1, 2009) UC Berkeley News
[Note that UC Berkeley graduate student Alistair Boettiger was also part of this research, though he’s not named in any of the quotes above.]
Perhaps our own initial impulse or attraction to art is also “an epiphenomenon reflecting neural activity” that is “incidental to the [person].” The irritant around which a pearl is formed.
Addendum: That, “The irritant around which a pearl is formed,” is a terrible analogy. Wrong at both ends. Blech . . . I need to go see the analogist and find out what’s wrong with my . . . oh, never mind.
-Julie
Coloring 
That’s neat. I’ve been a fan of these cellular automata shells for years, and have a copy of Meinhardt’s The Algorithmic Beauty of Sea Shells. Meinhardt was on exactly the right track about the inhibition-excition travelling-wave processes that generate these patterns, but postulated a mechanism that didn’t match any physical reality.
Comment by Ray Girvan — May 13, 2009 @ 9:36 am