All Creatures Great and Smart

Research reveals animals' brains to be bioengineering marvels

Carl T. Hall / SF Chronicle 27nov00

Nearly every important recent brain discovery comes from the study of simpler nervous systems in animals. But it seems those animal brain circuits aren't so simple after all.

Roaches, for example, listen with their knees.

Snakes can remember what they see.

And homing pigeons, with a brain the size of a pecan, can sniff their way home with such efficiency that scientists hope to copy it in futuristic route- finding devices.

These creatures were among dozens of species represented at the recent annual meeting of the Society for Neuroscience, an international research showcase that reflected growing appreciation of the bioengineering marvels in nature.

Such research goes far beyond the traditional use of mice, rats and other laboratory animals as mere models of the human brain. Now, scientists are tackling a remarkably diverse array of animal behaviors - partly for their own sake, partly in hopes that the neural circuitry might inspire futuristic "smart" devices to aid humans.

Robert Wyttenberg, a neurobiologist at Cornell University, has spent much of his research career studying hearing mechanisms of insects - tiny but sophisticated systems that might lead to powerful, implantable hearing aids. Crickets, for example, have evolved some advanced hearing mechanisms capable of detecting the faint ultrasound signals emitted by predatory bats.

Wyttenberg's studies led him to check hearing abilities in other insects, including termites, which have limited auditory skills, and, most recently, roaches, whose hearing falls somewhere between that of termites and crickets.

"I'm interested generally in what makes insects work," Wyttenberg said. "For their size, they are very complex things."

The Madagascar cockroach, Gromphadorhina portentosa, hisses when disturbed, and males hiss during courtship and when facing rivals. While the behavior has been studied for years, Wyttenbach found that nobody had looked at how they hear.

"There's no obvious ear on the animal, as there is on a cricket, but we know from their behavior that they have to hear," he said.

He examined the roach's legs in some detail, injecting them with fluorescent markers that allowed him to trace an elaborate neuronal circuitry around sound-detecting structures known as the subgenual organs, an array of sensory receptors located near enlarged air tubes of the tibia, near the middle of the leg.

For David A. Holtzman, assistant professor of brain and cognitive sciences at the University of Rochester, the big questions have to do with understanding the brainpower of snakes.

After a series of experiments with corn snakes, he has shown for the first time that snakes can pick up and remember visual cues in their environment, and that their characteristic tongue-flicking speeds up when something novel appears.

"People may think snakes are these slithery things that wander around and fortuitously somehow survive. What we are finding is that snakes learn from their vision," he said.

Other neuroscientists take on subjects with higher visibility.

Lori Marino of Emory University, working in collaboration with Navy marine mammal researchers in San Diego, has been conducting a investigation of dolphin neuroanatomy. It turns out the animals not only have large brains, but also a large cerebellum. That's an evolutionarily ancient structure found at the base of the mammalian brain, which helps control movement.

A big cerebellum could make sense for animals that rarely seem to hold still, Marino said.

"They live a very fast lifestyle," she said. "We can only guess why they have this particular brain structure, but maybe it's because they have to track a lot of information very fast."

Scientists have had a hard time keeping up with every discovery.

"We don't know a whole lot yet about what goes on in the brains of dolphins, " Marino said. "We do know they took a completely different evolutionary path to having big brains, and to me that's just very interesting."

Dolphins emit a rapid series of clicks for echolocation, bouncing sounds off objects and measuring their distance from how the sounds return. Marino speculates that a large part of the dolphin's brain may be dedicated to "acoustic signal processing."

The advent of sophisticated brain-imaging techniques has shed light on some mysteries of animal behavior that have captivated humans for centuries.

Vern Bingman, a behavioral neuroscientist at the J.P. Scott Center for Neuroscience, Mind and Behavior at Bowling Green State University in Ohio, has been trying to piece together the guidance system of homing pigeons.

Functional MRI and other standard neuroimaging tools are difficult to use for the study of bird brains at work in a natural setting. In the latest study,

summarized at the neuroscience meeting, Bingman and colleagues took advantage of certain chemical traces of pigeon brain activity, in particular a protein called ZENK. Levels of the protein can be calibrated and turned into visual images. The same technology has been used to study learning and memory circuits in songbirds.

In the new experiment, pigeons were taken to a location nine miles from home. Some were driven back, others were released and had to find their own way. Comparison of ZENK levels in the two groups of birds suggested that homing occurs within certain areas of the pigeon hippocampus, a brain region long known to be critical in memory. The surprise was that other regions also kick in, such as the para-olfactory lobe, suspected of playing a role that may guide the pigeon's flight trajectory.

It's also clear that homing pigeons are equipped with elaborate chemosensory powers, giving birds the ability to "sniff" out a route from atmospheric signals.

How it all works is still a mystery. Trying to solve it, Bingman says, is no mere flight of fancy, either. He maintains that pigeon studies might help scientists understand route-finding at a more basic level than would otherwise be possible. And once the mechanisms of so-called "spatial memory" become clear, it might be possible to find ways to enhance it.

That might lead to new ways of treating memory loss caused by Alzheimer's disease. Bingman said he envisions "pocket-sized or even smaller" electronic homing devices modeled after bird-brained tricks of navigation.

But like many of his peers, Bingman admits that the potential relevance to humans is somewhat beside the point, although useful in securing financial support for more research.

Sounding an awestruck tone, he recalled experiments when he put homing pigeons to the test in mountainous regions of Italy.

"You drive out 200 kilometers in the wine country and let them out, and they're back home before you are," he said. "It's really remarkable."

COMPARING BRAINS The brains of mammals come in a large variety of sizes, shapes and complexity.

(These photographs show relative sizes.) New research into this diverse array is yielding some surprising findings about brain and behavior. The research, while important in its own right, might also be used to design "smart" devices to aid humans. Cerebrum Area of brain where most higher brain functions occur.Cerebellum An evolutionarily ancient structure that controls movement and equilibrium.

E-mail Carl T. Hall at carlhall@sfchronicle.com