Is Bigger Better?
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Source:
R&D
Brains Study Brains
DISCOVER Vol. 26 No. 07 | July 2005 | Mind & Brain
http://www.discover.com/issues/jul-05/rd/brains-study-brains/
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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
Print Resources
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"Is Bigger Better?" An in-depth look at brain evolution can be
found in William Calvin's book A Brief History of the Mind: From Apes to
Intellect and Beyond (Oxford University Press, 2004).
"Reciprocal Evolution of the Cerebellum and Neocortex in Fossil Humans."
Anne H. Weaver in Proceedings of the National Academy of Sciences, Vol.
102, No. 10, pages 3576-3580; March 8, 2005.
For a detailed look at preventing brain cell death, see "Soluble CPG15
Expressed During Early Development Rescues Cortical Progenitors From
Apoptosis." Ulrich Putz et al. in Nature Neuroscience, Vol. 8, No. 3,
pages 322-331; March 1, 2005.
"Juggling Info." "How Many Variables Can Humans Process?" Graeme S.
Halford et al. in Psychological Science, Vol. 16, No. 1, pages 70-76;
January 2005.
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