In the Sept. 26 issue of Science, Salk Institute professor Terrence Sejnowski and University of Cambridge professor Simon Laughlin argue that the human brain has evolved to operate as an enormously efficient "hybrid device," capable of making far more sophisticated computations than the most powerful computers, and the long-distance communication systems in brains have been optimized by evolution for energy efficiency.
"In the past, we were only able to look at brain function by looking at single neurons or local networks of neurons. We were only able to see the trees, so to speak," said Sejnowski. "With breakthroughs in recording techniques including brain imaging, which gives us a global picture of brain activity, and advances in computational neurobiology, we can now take a more global perspective. We're looking at the entire forest, and we're asking the question: How has the forest evolved?"
As the brain has evolved over millions of years, according to Sejnowski, it has become amazingly efficient and powerful. He says that nature has "optimized the structure and function of cortical networks with design principles similar to those used in electronic networks." To illustrate the brain's tremendous capacity, Sejnowski and Laughlin state that the potential bandwidth of all of the neurons in the human cortex is "comparable to the total world backbone capacity of the Internet in 2002."
But they point out that simply comparing the brain to the digital computers of today does not adequately describe the way it functions and makes computations. The brain, according to Sejnowski, has more of the hallmarks of an "energy efficient hybrid device."
"These hybrids offer the ability of analog devices to perform arithmetic functions such as division directly and economically, combined with the ability of digital devices to resist noise," he writes in Science.
"This is an important era in our understanding of the brain," according to Sejnowski. "We are moving toward uncovering some of the fundamental principles related to how neurons in the brain communicate. There is a tremendous amount of information distributed throughout the far-flung regions of the brain. Where does it come from? Where does it go? And how does the brain deal with all of this information?
"These are questions we've not been able to address on a comprehensive basis until now. I believe that over the next decade, we will begin to develop some answers."
The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent, nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. The institute was founded in 1960 by Jonas Salk, M.D., with a gift of land from the City of San Diego and the financial support of the March of Dimes Birth Defects Foundation.