Vertebrate brains generally contain two kinds of tissue: gray matter and white matter. Gray matter contains local networks of neurons that are wired by dendrites and mostly nonmyelinated local axons. White matter contains long-range axons that implement global communication via often myelinated axons. What is the evolutionary advantage of segregating the brain into white and gray matter rather than intermixing them?

In this study, the authors postulate that brain functionality benefits from high synaptic connectivity and short conduction delays—the time required for a signal from one neuron soma to reach another. Using this postulate, they show quantitatively that the existence of many fast, long-range axons drives the segregation of the brain into gray and white matter. The theory not only provides a possible explanation for the structure of various brain regions such as cerebral cortex, neostriatum, and spinal cord, but also makes several testable predictions such as the scaling estimate of the cortical thickness.

The theory is based on the idea that maximum brain function requires a high level of interconnectivity among brain neurons but a low level of delays in the time it takes for signals to move through the brain ("conduction delays").

Based on no fewer than 62 mathematical equations and expressions, the theory ("Segregation of the Brain into Gray and White Matter: A Design Minimizing Conduction Delays") provides a possible explanation for the structure of various neurological regions including the cerebral cortex and spinal cord.

The research was carried out at Cold Spring Harbor Laboratory on Long Island by theoretical neuroscientist Dmitri Chklovskii and graduate student Quan Wen. "We present our theory in Results, which is organized into seven sections. In the first, we consider competing requirements between small conduction delays and high connectivity in local circuits. We show that local conduction delay limits the size of the local network with all-to-all potential connectivity to the size of the cortical column. The second section models full brain architecture as a small-world network, which combines high local connectivity with small conduction delay. We derive a simple estimate of conduction delay in global connections as a function of the number of neurons. In the third section, we consider spatially integrating local and global connections. We argue that mixing local and global connections substantially increases local conduction delay, while the global conduction delay may be unaffected. In the fourth section, by minimizing local conduction delay we derive a condition under which white/gray matter segregation reduces conduction time delays. The fifth section gives a necessary condition for the segregated design to be optimal, and an example of such design is given in the sixth section. Finally, the seventh section restates our results in terms of the numbers of neurons, interneuronal connectivity, and axon diameter."

The study was published in the December issue of PLoS Biology and is available >at *Segregation of the Brain into Gray and White Matter: A Design Minimizing Conduction Delays* by Quan Wen and Dmitri B. Chklovskii. PLoS Biology, december 30, 2005. DOI: 10.1371/journal.pcbi.0010078

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> synaptic plasticity: how experiences rewire the brain. january 23, 2003
> genes, neurons, internet: organizing principles of networks. november 11, 2002
> neurogenesis: observed in human adult brain. march 6, 2002

imago
> about connections, conductions and delays

sonic flow
> conduction delays [stream]
conduction delays [download]

The most prominent of the Milky Way's satellite galaxies - a pair of galaxies called the Magellanic Clouds - appears to be interacting with the Milky Way's ghostly dark matter to create a mysterious warp in the galactic disk that has puzzled astronomers for half a century.

The warp, seen most clearly in the thin disk of hydrogen gas permeating the galaxy, extends across the entire 200,000-light year diameter of the Milky Way, with the sun and earth sitting somewhere near the crease. Leo Blitz, professor of astronomy at the University of California, Berkeley, and his colleagues, Evan Levine and Carl Heiles, have charted this warp and analyzed it in detail for the first time, based on a new galactic map of hydrogen gas (HI) emissions.

They found that the atomic gas layer is vibrating like a drum, and that the vibration consists almost entirely of three notes, or modes.

Astronomers previously dismissed the Magellanic Clouds - comprised of the Large and Small Magellanic Clouds - as a probable cause of the galactic warp because the galaxies' combined masses are only 2 percent that of the disk. This mass was thought too small to influence a massive disk equivalent to about 200 billion suns during the clouds' 1.5 billion-year orbit of the galaxy.

Nevertheless, theorist Martin D. Weinberg, a professor of astronomy at the University of Massachusetts, Amherst, teamed up with Blitz to create a computer model that takes into account the Milky Way's dark matter, which, though invisible, is 20 times more massive than all visible matter in the galaxy combined. The motion of the clouds through the dark matter creates a wake that enhances their gravitational influence on the disk. When this dark matter is included, the Magellanic Clouds, in their orbit around the Milky Way, very closely reproduce the type of warp observed in the galaxy.

"The model not only produces this warp in the Milky Way, but during the rotation cycle of the Magellanic Clouds around the galaxy, it looks like the Milky Way is flapping in the breeze. >from *milky way galaxy is warped and vibrating like a drum*. january 9, 2006

related context
> the local group of galaxies.
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> andromeda's thin sheet of satellites - dark matter filaments or galactic cannibalism?. january 11, 2006
> scientists 'rave-ing' about most ambitious star survey ever. dark matter dominates the total mass of our home galaxy, the milky way. january 11, 2006
> astronomers shed surprising light on our galaxy's black hole. january 10, 2006
> black holes and galaxies. january 27, 2003
> milky way center: a supermassive black hole. october 22, 2002

imago
> do you hear the drum?

sonic flow
> galactic warp [stream]
galactic warp [download]

"LSD is the closest, the most dense, the most mysterious link between the material and the spiritual world. A hardly visible trace of LSD matter is capable of evoking heaven or hell in the spiritual world, i.e. in human consciousness." Albert Hofmann

On the occasion of the 100th birthday of Dr. Albert Hofmann on 11 January 2006, the Gaia Media Foundation stages an International Symposium on the most widely known and most controversial discovery of this outstanding scientist.

LSD - three letters that changed the world. Since 19 April 1943, the day Swiss chemist Dr. Albert Hofmann discovered this psychoactive substance, millions of people all over the world have experienced a higher reality with profound and psychological insights and spiritual renewal; created innovative social transformation, music, art, and fashion; were healed from addiction and depression; experienced enlightened insights into the human consciousness.

Some 60 years after Dr. Hofmann’s far-reaching discovery more than 80 renowned experts from all over the world will examine the LSD phenomenon from every angle, in an effort to put up facts against prejudice. On Friday, 13 January, the drug’s history is in the foreground of discussions ("From the Plants of the Gods to LSD"). On Saturday, 14 January, a look will be taken at "The Ecstatic Adventure". On Sunday, 15 January, it will be about "New Dimensions of Consciousness". For that, the international consciousness research’s elite will come: from the USA, among others, Rick Doblin, Alexander Shulgin and Ralph Metzner; from Europe Guenter Amendt, Christian Raetsch and Franz Vollenweider. Moreover prominent artists and witnesses of the times like Alex Grey, Ulrich Holbein and Barry Miles will travel to Basel in order to give detailed accounts of their personal experiences with LSD and its influence on the arts and culture. >from *Consciousness Researchers in Basel. LSD – Problem Child and Wonder Drug* January 13th - 15th, 2006

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> technoetic arts: an international journal of speculative research. may 9, 2003
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imago
> lsd: too hot to handle?
turn on, tune in, drop out

sonic flow
> lsd [stream]
lsd [download]

A single unifying physics theory can essentially describe how animals of every ilk, from flying insects to fish, get around, researchers at Duke University's Pratt School of Engineering and Pennsylvania State University have found. The team reports that all animals bear the same stamp of physics in their design.

The researchers show that so-called 'constructal theory' can explain basic characteristics of locomotion for every creature -- how fast they get from one place to another and how rapidly and forcefully they step, flap or paddle in relation to their mass. Constructal theory is a powerful analytical approach to describing movement, or flows, in nature.

They said their findings have important implications for understanding factors that guide evolution by suggesting that many important functional characteristics of animal shape and locomotion are predictable from physics.

The findings challenge the notion that fundamental differences between apparently unrelated forms of locomotion exist. The findings also offer an explanation for remarkable universal similarities in animal design that had long puzzled scientists, the researchers said.

"The similarities among animals that are on the surface very different are no coincidence," said Adrian Bejan, J. A. Jones Professor of Mechanical Engineering at Duke's Pratt School. "In fact, animal locomotion is no different than other flows, animate and inanimate: they all develop in space and in time such that they optimize the flow of material." In the case of animal locomotion, this means that animals move such that they travel the greatest distance while expending the least amount of energy, he said.

"From simple physics, based only on gravity, density and mass, you can explain within an order of magnitude many features of flying, swimming and running," added James Marden, professor of biology at Penn State. "It doesn't matter whether the animal has eight legs, four legs, two, even if it swims with no legs."

First conceived by Bejan and published in 1996, the constructal law arises from the basic principle that flow systems evolve so as to minimize imperfections -- energy wasted to friction or other forms of resistance -- such that the least amount of useful energy is lost.

The findings may have implications for understanding animal evolution, Marden said. One view of evolution holds that it is not a purely deterministic process; that history is full of chance and historical contingency. It is the idea purported by Steven Jay Gould and others that if you were to "rewind the tape" and run it again, evolution would proceed down a different path, Marden said.

"Our finding that animal locomotion adheres to constructal theory tells us that -- even though you couldn't predict exactly what animals would look like if you started evolution over on earth, or it happened on another planet -- with a given gravity and density of their tissues, the same basic patterns of their design would evolve again," Marden said. >from *Unified Physics Theory Explains Animals' Running, Flying And Swimming*. December 30, 2005

related context
> the history of evolutionary thought in biology.
> computer model of e-coli: predict evolution of bacteria. november 26, 2002
> landmark in evolutionary biology: mechanism to introduce new body designs. february 22, 2002

imago
> aniamal motion constructal law

sonic flow
> constructal law [stream]
constructal law [download]