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friday :: august 25, 2006
evolutionary path: scale-free networks

The architecture that pervades biological networks gives them an evolutionary edge by allowing them to evolve to perform new functions more rapidly than an alternative network design, according to computer simulations conducted at the University of Chicago.

Scientists have found the same intricate network architecture of evolution just about everywhere they look. This architecture characterizes the interaction network of proteins in yeast, worms, fruit flies and viruses, to name a few. But this same architecture also pervades social networks and even computer networks, affecting, for example, the functioning of the World Wide Web.

“These results highlight an organizing principle that governs the evolution of complex networks and that can improve the design of engineered systems,” wrote co-authors, Panos Oikonomou and Philippe Cluzel.

This organizing principle is what scientists call a “scale-free design.” A diagram of this design resembles the route maps of airline companies. “You have hubs that are highly linked with airplanes going in and out of those hubs,” Oikonomou said. But then smaller airports also exist that have far fewer connections, and there are various scales of connections in between.

Oikonomou and Cluzel initiated his project to find out if network design conferred any kind of evolutionary advantage. They created a Darwinian computer simulation to compare the evolvability of this scale-free network design with a more random design in which all network components have approximately the same number of connections. They programmed this computer world to have random mutations and natural selection operate on its digital populations, then compared how long it took the two types of networks to evolve the ability to perform a new task.

The populations organized in scale-free networks evolved rapidly and smoothly, while randomly organized networks evolved slowly and in spurts following a succession of rare and beneficial random events. “They followed drastically different evolutionary paths,” Cluzel said. Cluzel plans to conduct laboratory experiments on bacteria to test the validity of the organizing principle he and Oikonomou have identified via their simulations.

Their goal was to better understand biological evolution, but social and economic networks also display a scale-free architecture. “These networks can be people, they can be molecules, they can be whatever you like,” Cluzel said. >from *Digital World Reveals Architecture of Evolution*. August 7, 2006

related context
social network theory to the test. the interaction between social network structure and collective problem solving. august 10, 2006
> coupled oscillators -that is, entities capable of responding to each other's signals- will spontaneously self-organize. april 9, 2003
> small-world networking. february 4, 2003
> organizing principles of networks. november 11, 2002
> the new science of networks. june 6, 2002

tim miller gets trapped in a free-scale network hub

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friday :: august 18, 2006
brain adaptive rewiring

A new discovery shows that the brain rewires itself following an experience. The research further shows that this process of creation, testing, and reconfiguring of brain circuits takes place on a scale of just hours, suggesting that the brain is evolving considerably even during the course of a single day.

Scientists know that the strength of the connections between neurons changes to shape memories. They also know that the developing brain has a high level of plasticity as neurons forge connections with other neurons.

This new research goes further, investigating how neurons choose their connections with neighboring neurons. Researchers Henry Markram and Jean-Vincent Le Bé found that connections between neurons switch rapidly on and off, leading to a form of adaptive rewiring in which the brain is engaged in a continuous process of changing, strengthening and pruning its circuitry.

Studying neuron clusters from the neocortex of neonatal rats, Markram and Le Bé found that instead of growing preferentially towards specific receivers, neurons actually have no particular affinity for any other neuron, but instead remain in a state of perpetual readiness to reconfigure circuits. They found that over the course of just a few hours, connections are formed and re-formed many times.

"The circuitry of the brain is like a social network where neurons are like people, directly linked to only a few other people," explains Markram. "This finding indicates that the brain is constantly switching alliances and linking with new circles of "friends" to better process information."

In their samples, the rewiring process was occurring continuously at a slow pace. By exciting the sample with glutamate, they found that the rate increased markedly. This suggests that with a strong new experience, the brain accelerates its reconfiguration process, allowing new connections to be made, tested, and strengthened, and weaker ones removed so that the brain is quickly better adapted to the new situation.

"This continual rewiring of the microcircuitry of the brain is like a Darwinian evolutionary process," notes Markram, "where a new experience triggers a burst of new connections between neurons, and only the fittest connections survive." >from *Rewiring the mammalian brain -- neurons make fickle friends*. new discovery from the Brain Mind Institute of the EPFL (Ecole Polytechnique Federale de Lausanne). August 7, 2006

related context
brain cells may have stem-cell-like potential. august 16, 2006
> new method shows that neocortical nerve cells are not renewed. neocortical neurogenesis in humans is restricted to development. august 11, 2006
> pure novelty spurs the brain. august 2, 2006
> 'mix of different lengths of neural projections is essential'. august 1, 2006
> researchers watch brain in action. july 27, 2006
> how the brain turns on innate behavior. july 27, 2006
> predecessor neurons. july 22, 2006
> genes in the brain change with experience at every age. may 12, 2006
> how brain cells work. april 28, 2006
> why the brain has gray and white matter. january 27, 2006
> female cycle and brain expansion. november 18, 2005
> cell death promotes learning growth. december 17, 2003
> synaptic plasticity: how experiences rewire the brain. january 23, 2003

perpetual readiness to reconfigure circuits

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friday :: august 11, 2006
ninety-eight percent of gaza's children experience or witness war trauma

Most children in the Gaza Strip have been tear gassed, have had their homes searched and damaged, and have witnessed shooting, fighting and explosions. Many have been injured or tortured as a result of chronic war that spans generations, says a recent Queen's University study.

According to the study, there is a pattern of violence against Palestinian children in the Gaza Strip that has serious and debilitating psychiatric and psychological effects.

"Gaza has been an occupied territory for a long time, and still is; Israel controls its borders, its air and water access. It has been described as a vast open-air detention centre" says Queen's community health and epidemiology researcher John Pringle. "Bombs are being launched into Gaza during this latest eruption of Middle East violence, but are being ignored in light of other crises."

The Psychological Effects of War on Palestinian Children is Pringle's Master's thesis and the only study of its kind, analyzing data from The Gaza Child Health Survey to describe relationships between war trauma and psychological problems in children.

According to the study, a child in Gaza who has had a severe head injury has 4 times the risk of emotional disorder. A child who has been severely beaten has 3.9 times the risk of Attention Deficit Hyperactivity Disorder. A child who has witnessed friends injured or killed has 13 times the risk of Post Traumatic Stress Disorder. A child in a refugee camp has 5 times a greater chance of witnessing traumatic events and 4 times a greater chance of direct physical trauma.

"Children comprise 47 per cent of Gaza's population and are extremely vulnerable," Pringle adds. "It seems the international community is neglecting them, that somehow Palestinian children don't deserve the protections guaranteed under the Geneva Convention and humanitarian law. We must remember that where we drop our bombs, plant our landmines, and aim our guns, is where children are born, play, and go to school."

Mr. Pringle is also a member of Doctors Without Borders (MSF). MSF is an emergency medical humanitarian aid organization that primarily works in war-zones with populations in danger, usually in refugee camps. It was awarded the Nobel Peace Prize in 1999. >from *98 per cent of Gaza’s children experience or witness war trauma - Queen’s study* First of its kind, study implores an end to political violence for Gaza’s “forgotten” children traumatized by chronic war. July 27, 2006.

related context
chemical warfare ravages mental health of iranian civilians. august 1, 2006
> warfare in the cities and settlement camps of palestine. june 9, 2006
> medical ethics and guantanamo bay. march 24, 2006
> 'art has the potential to unite different cultures'. december 9, 2005
> 'global war on terror is diverting the world's attention from the central causes of instability'. january 14, 2005
> mortality before and after the 2003 invasion of iraq. november 19, 2004
> deadly medicine. november 5, 2004
> making differences. january 25, 2004
> guess who died. october 6, 2003
> art bridge between palestine and the outside world. july 3, 2002
> mirroring evil. march 18, 2002
> present tense. january 9, 2002

stop war violence

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friday :: august 4, 2006
auditory code: how brain processes sound

Scientists at Carnegie Mellon University have discovered that our ears use the most efficient way to process the sounds we hear. These results represent a significant advance in understanding how sound is encoded for transmission to the brain.

The research provides a new mathematical framework for understanding sound processing and suggests that our hearing is highly optimized in terms of signal coding —the process by which sounds are translated into information by our brains— for the range of sounds we experience. The same work also has far-reaching, long-term technological implications, such as providing a predictive model to vastly improve signal processing for better-quality compressed digital audio files and designing brain-like codes for cochlear implants, which restore hearing to the deaf.

To achieve their results, the researchers took a radically different approach to analyzing how the brain processes sound signals. Abstracting from the neural code at the auditory nerve, they represented sound as a discrete set of time points, or a "spike code," in which acoustic components are represented only in terms of their temporal relationship with each other. That's because the intensity and basic frequency of a given feature are essentially "kernalized," or compressed mathematically, into a single spike. This is similar to a player piano roll that can reproduce any song by recording what note to press when the spike code encodes any natural sound in terms of the precise timings of the elemental acoustic features. Remarkably, when the researchers derived the optimal set of features for natural sounds, they corresponded exactly to the patterns observed by neurophysiologists in the auditory nerves.

"We've found that timing of just a sparse number of spikes actually encodes the whole range of nature sounds, including components of speech such as vowels and consonants, and natural environment sounds like footsteps in a forest or a flowing stream," said Michael Lewicki, associate professor of computer science at Carnegie Mellon and a member of the Center for the Neural Basis of Cognition (CNBC). "We found that the optimal code for natural sounds is the same as that for speech. Oddly enough, cats share our own optimal auditory code for the English language."

"Our work is the only research to date that efficiently processes auditory code as kernalized spikes," said Evan Smith, a graduate student in psychology at the CNBC.

Until now, scientists and engineers have relied on Fourier transformations —initially discovered 200 years ago— to separate and reconstitute parameters like frequency and intensity as part of traditional sound signal processing.

Smith and Lewicki's approach dissects sound based only on the timing of compressed "spikes" associated with vowels (like cat vocalizations), consonants (like rocks hitting one another) and sibilants (ambient noise).

The authors' research combines computer science, psychology, neuroscience and mathematics. >from *Carnegie Mellon Scientists Show How Brain Processes Sound*. Landmark Results Could Improve Devices from iPods to Cochlear Implants. February 23, 2006

related context
sound-analysis breakthrough. extremely high-resolution time-frequency analysis. july 26, 2006
> brain frequency map. researchers map out numerous areas in the brain where sound frequencies are processed. june 22, 2006
> sound of silence activates auditory cortex. auditory imagery is the subjective experience of hearing in the absence of auditory stimulation. 2005
> sonification. data sonification is becoming one of the most promising analysis tools, since sounds can summarize significant amounts of information and can be characterized, stored and studied in a simpler and easier way with respect to other data representations. november 25, 2005
> how we hear. discovered how tiny cells in the inner ear change sound into an electrical signal the brain can understand. may 7, 2002

auditory-protective follie

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