See Inside March 2010

Limits of Perception

Editor in Chief Mariette DiChristina introduces the March 2010 issue of Scientific American

Aaron Goodman

“Every man takes the limits of his own field of vision for the limits of the world.”
—Arthur Schopenhauer, Studies in Pessimism

Riding in a Manhattan subway car the other morning, I read that quote by 19th-century German philosopher Arthur Schopenhauer on one of the transit authority’s “Train of Thought” posters. It amused me that I had actually gone underground to see the light. That is, Schopenhauer’s words captured clearly what I had been only vaguely mulling about some of this issue’s major features and what they represent: the utility of looking at an area of science anew by coming at it from a different perspective. In this, I realize, I am hardly the first person to notice that when attempting to solve a problem, changing your physical vantage point or mental framework can loft you past perceived limits. In some cases, it can be difficult to recognize evidence that may be right before your eyes because you fail to appreciate it for what it is.

And so it was with the subject of this month’s cover story. What scientists once thought was unremarkable cellular “noise” in neuron signaling has come to be viewed as important to overall system-wide functioning in the brain. It’s common, and completely understandable, for researchers to strip noise from any signals they are trying to measure. But neuroscientist Marcus E. Raichle, author of “The Brain’s Dark Energy,” was one of the first to wonder whether the noise itself had meaning. As he later said at a conference on brain network dynamics, “It turns out that this is yet one more signal in the biological world whose ‘noise’ is highly important and is very information rich.”

Raichle, a pioneer in the use of brain imaging, and his colleagues have observed that in brains at “rest”—when you are not thinking of anything in particular or even when you are asleep—dispersed areas are still buzzing with communication. This intrinsic activity he calls the brain’s default mode. Determining the exact role of this previously unappreciated “dark energy” is an ongoing area of study, but it appears to be involved in how the brain prepares for future events that involve conscious processing. Disruptions of such activity may underlie certain brain disorders as well.

In another feature article, geochemist Robert M. Hazen also proposes a new view—one applied to our understanding of how Earth’s deep geohistory shaped its mineral riches. Once there were mere dozens of minerals in the universe, but today our planet has more than 4,400 known mineral species. How did that diversification happen?

In “Evolution of Minerals,” Hazen suggests we reconsider mineralogy, which does not traditionally look beyond minerals’ timeless properties. He and his colleagues use “Earth’s history as a frame for understanding minerals and the processes that created them.” With this long-range lens, it becomes clear that the rise of life and its metabolic activities dramatically directed our planet’s uniquely diverse mineral kingdom. Up to two thirds of the mineral species co-evolved with life through a series of epochs. The “rock of ages” takes on a whole new meaning.

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