Modeling the restless brain
Indiana University neuroscientists Olaf Sporns and Christopher Honey find the 98 percent of brain activity that other researchers consider just background noise to be fascinating and important.
Brains are always active, even when people are at rest. In this "resting state," waves of neural activity ripple through the brain, creating fluctuating and ever-changing patterns. Sporns and Honey's work on modeling this brain activity sheds new light on how and when these mysterious fluctuations occur and offers insights into what the brain does while idle.
"Some people see the brain in terms of inputs and outputs, like a computer. If you provide an input, you'll get a particular output," said Honey, a doctoral student in IU Bloomington's Department of Psychological and Brain Sciences. "We take a different view. We believe that even in the absence of an external stimulus, there are very important processes going on in the brain which affect the stimulus-responses that the brain will produce. We believe that ongoing spontaneous activity should be studied in itself. Other researchers consider this to be unimportant 'noise' that should be filtered out."
Honey and Sporns, associate professor in the Department of Psychological and Brain Sciences, took a close look at the spontaneous activity of the brain at rest. With their computational approach -- which involved creating a large-scale computer model of the brain of a macaque monkey -- they demonstrated that the shape and pattern of the fluctuations are determined by the brain's wiring diagram, its neuroanatomy.
Their model also can show how slow 5- to 10-second fluctuations of activity emerge naturally from much faster, chaotic neural interactions that typically last only a few milliseconds.
"Our model suggests that the cortical resting state is not time-invariant, but instead contains rich and interrelated temporal structure at multiple time scales that is shaped by the underlying structural topology," Sporns and Honey wrote in an article appearing this week in the Proceedings of the National Academy of Sciences early edition online.
The article, available at http://www.pnas.org/cgi/doi/10.1073/pnas.0701519104, includes a link to a movie that visualizes what spontaneous fluctuations in the monkey's brain would look like. Co-authors of the article are Rolf Kötter, a neuroanatomist at Radboud University in Nijmegen in the Netherlands, and Michael Breakspear, a cognitive neuroscientist at the University of New South Wales in Australia.