Net heads: huge numbers of brain cells may navigate small worlds

Science News,  Feb 17, 2007  by Bruce Bower

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In Friston's view, Bassett's findings demonstrate the organized but flexible nature of intrinsic brain activity but not its purpose.

In an upcoming NeuroImage, neuroscientists Alexa M. Morcom and Paul C. Fletcher, both of the University of Cambridge, argue that intrinsic activity holds no special significance in the brain. They say that scientists know virtually nothing about thinking that occurs spontaneously and should stick to studies of brain responses during mental tasks.

Other researchers see much significance for background activity in promoting efficient thinking. For instance, a team led by neuroscientist Michael D. Greicius of Stanford University School of Medicine reported in 2004 that memory problems in people with mild Alzheimer's disease coincide with unusually low amounts of intrinsic activity in several memory-related brain areas.

Whether or not the brain's dark energy proves important, neuroscientists are increasingly confident that communication among the brain's 100 billion neurons requires surprisingly few steps. It may well be a small world in there after all.

GLOBAL TIES--In a model of neurons arranged on a sphere and engaging in random activity (left), the units form a small-world structure. Researchers then transformed a spherical snapshot and electrical-activity recordings of simulated neural activity (middle) into a more complex map of brain networks that still exhibited small-world characteristics.

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