Net Heads
Huge numbers of brain cells may navigate small worldsAbout 40 years ago, the late psychologist Stanley Milgram tapped into the commonsense notion that "it's a small world." Milgram asked 60 people to send a folder to a certain individual whom none of them knew. Participants were given a little information about the target person and asked to mail the folder to a friend or acquaintance who, in their view, was more likely to know the stranger than they were. Each recipient of the folder was asked to do the same, until the material reached its destination
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Strogatz and Watts also demonstrated the relevance of the small-world idea to the array of 282 brain cells in worms called nematodes.
Small-world networks have a distinctive structure: There's a cluster of nodes, each connected to its immediate neighbors, with a few that connect to distant nodes. This structure enhances the power and efficiency of these systems, Strogatz and Watts argued.
More and more neuroscientists agree. Motivated by Milgram and his mathematical progeny, researchers are now devising models grounded in the small-world effect to explain how the human brain works. These scientists are looking for small-world setups within the brain's massive, interconnected cell networks and for moment-to-moment electrical manipulations that, they suspect, foster thinking and learning. Their efforts are a sharp departure from popular brain-imaging efforts to pinpoint neural niches that specialize in particular mental capabilities.
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For now, remarks Sporns, the new findings indicate that related brain networks operate at different electrical frequencies, each of which acts as a unique channel for transmitting information. The brain needs no central-control mechanism to direct mental life; interactions within and among networks do the trick.
The possibility that the brain steeps itself in flexible, chaotic activity is "an attractive idea," notes neuroscientist Karl Friston of University College London. He says that Bassett's team now needs to formulate a theory of how low- and high-frequency synchronized networks collectively respond to mental challenges.
Perking up
The notion that the brain thrives on chaos, in a mathematical sense, comes as no shock to neuroscientist Walter J. Freeman of the University of California, Berkeley. For the past 20 years, he has argued that the brain churns out a cascade of chaotic electrical activity that serves as a "get ready" state. From there, he theorizes, vast expanses of brain tissue shift into electrical-activity patterns that organize thought and perception.
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Both his group and Bassett's team have found hubs of particularly intense activity within networks of synchronized brain cells. These hubs arise where neural connections are especially numerous.
However, fMRI investigators such as Friston still see value in the search for brain regions with specialized duties. Activity hubs probably integrate information shuttled in from other brain locations, Friston proposes.
