Brains Study Brains

Sunday, July 24, 2005

Is bigger better?
Scientists know less about the human brain than any other part of the body, but recent studies suggest answers to three tough questions:

Why did hominin brains triple in size over the past 6 million years? William Calvin, a neurobiologist at the University of Washington in Seattle, argues that it all has to do with throwing a rock. To hit the target, the brain had to coordinate such variables as muscle movements, visual images, and the weight of the stone. Only an increase in brain size could make throwing—especially over long distances—accurate, he says. That neural circuitry was able to handle other complex matters: keeping track of social relationships, planning for the future, and developing language.

Then why did brains start to shrink 30,000 years ago? Paleoanthropologist Anne Weaver of Santa Fe Community College believes smaller brains are more efficient than the bulky brains that early Homo sapiens carried around. By comparing modern and ancient skulls, she found that the cerebellum, an area that acts as a switchboard for the rest of the brain, grew as overall brain size shrank. The big cerebellum allowed people to process and categorize information faster. “Once they had a certain population density, people needed to cope with a huge amount of social information,” she says. “You have to keep track of who’s who, whose territory is whose, who’s related to whom, and what kind of social obligations you’ve got.”

Can brains get bigger again? Experiments with mouse embryos suggest they can. MIT neurobiologist Elly Nedivi identified a protein that stops unused brain cells from pulling the trigger on a chemical cascade that ends their lives, thus preventing brains from becoming cluttered with dead-ending circuitry. In her experiments, mouse embryos treated with the protein CPG15 did not kill off their unused cells and grew brains up to 20 percent larger than normal. Nedivi believes the protein gives human brain cells more time to form connections and avoid death. In the future, CPG15 treatments may limit brain damage from concussions or such disorders as Alzheimer’s disease. —Zach Zorich

Juggling info
Surgeons, air traffic controllers, waitresses, and bus drivers—or anyone in a high-stress job—take in a steady flow of information that needs to be processed on the spot. But how much is too much? Cognitive scientists in Australia have concluded that humans can juggle four “chunks” of information at any given instant. After that, they become confused. Their next move is no more reasoned than flipping a coin.

Graeme Halford of the University of Queensland and his team presented bar graphs with information about cakes, cars, or clothing to students and academics and asked them questions. In one case, a graph showed that people generally prefer chocolate cake to carrot cake but that the degree of their preference changed when variables like icing or frozen or fat-free cake were introduced. When juggling four pieces of information, the subjects were consistently able to answer the questions correctly. With five variables or more, they could not.

What makes the experiment innovative, Halford says, is the graphs were presented in such a way that subjects could not consolidate data—what psychologists call chunking. Understanding these limits of human cognition can improve efficiency—and save lives. Halford hopes his findings will help in the design of high-stress work environments. “I think in the modern world, most jobs have a lot of complexity,” he says, “and no one knows how to deal with that complexity.” —Susan Kruglinski

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