Consult the Ratlas


For human navigators of the rat brain, neuroscientist Larry Swanson has published The Structure of the Rat Brain, a kind of extraordinarily detailed “roadmap” of the rodent’s gray matter. “Most people just call it ‘Ratlas,’ ” he says.

A digitized rat brain, one of 73 cross sections from Larry Swanson's Ratlas CD-ROM. The left side is a photo of the actual brain section; the right side is a "map" showing the various features of the brain at that level.
Rats may be able to memorize the twists and turns of a maze, but the researchers who study them sometimes need a little guidance.
For human navigators of the rat brain, neuroscientist Larry Swanson has prepared an extraordinarily detailed map, in the form of a book called The Structure of the Rat Brain.
“Most people just call it ‘Ratlas,’ ” quips Swanson, who is USC’s Milo Don and Lucille Appleman Professor of Biological Sciences.
Now in its second edition, the original $250 coffee-table-style book (which was first published in 1992) has shrunk down to a less clunky size, gained a CD-ROM companion and dropped to a research grant-friendly $90.
“The first edition had to be big in order to see the detail in the pictures,” Swanson says. “But this one comes with computer graphics files that you can load in your computer and explore.”
To make Ratlas, Swanson started with a single rat brain, infiltrated it with plastic to make it firm, and then cut it into 556 very thin slivers, using a machine much like the one that slices roast beef in a delicatessen. He chose 73 of those slices and meticulously examined them under a microscope to prepare minutely detailed maps of each.
“Then we entered it into a computer, and with the computer’s software we are now working to generate 3-D graphics of the entire rat brain,” he says.

Who wants to find his way around a rat’s brain anyway?
Neuroscientists, that’s who, says Swanson, who is also dean of research in the College of Letters, Arts and Sciences. Because they can’t experiment on humans, most brain researchers work with rats. Rat brains have the same basic parts as the human brain, although they weigh only 2 grams compared to a human brain’s 1,500 grams.
“These are guides for all of us who are mapping the circuits of the rat brain,” Swanson says.

Brain circuits are made up of nerve cells that communicate with each other chemically. The chemicals that mediate the transmission of impulses between nerve cells are called neurotransmitters. Re-searchers want to identify the circuits responsible for all of the functions controlled by the brain.
Swanson, for example, does research on motivated behavior — such as hunger and thirst — by searching for the circuits in the brain that control these behaviors.
“We all eat, but some of us overeat while others get anorexia,” the researcher says. “If we know which circuits control hunger, we may be able to correct problems with drugs that fine-tune the neurotransmitters.”


To Scan or to Slice?

CUTTING UP BRAINS is nothing new. Renaissance physician Andreas Vesalius carefully sliced up a human brain so an artist could sketch the structure for a classic anatomy book published in 1543. Several decades earlier, Leonardo da Vinci produced drawings, unpublished at the time, indicating that he had done the same thing.
But with the availability of modern instruments such as CAT scans or MRIs — which can peer inside the brain — why go to all the trouble of physically slicing rat brains to study the structure?
Because the microscopic resolution of the brain structure is about 1,000 times finer than what can be achieved using MRI or CAT scans, says neuroscientist Larry Swanson.
“With a brain scan, you can’t see individual brain cells like you can with a microscope,” he says. “The resolution with an MRI is about the same as with the human eye.”





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Rat Brain Illustration courtesy of Larry Swanson

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