Rat whiskers: a science frontier

Researchers study rodents for clues on brain function, robot explorers

November 08, 2006|By Jeremy Manier | Jeremy Manier,CHICAGO TRIBUNE

CHICAGO -- The most surreal gadget in Mitra Hartmann's robotics lab, the one that prompts an instinctive double-take from visitors, is a jumble of metal sensors and wires attached to a single, wispy rat whisker.

It looks like part of a freakish rodent cyborg, but that's not the goal for Hartmann and her team at Northwestern University. They're after something more practical - robotic whiskers that can pick out the shapes of objects by touch, just as rats do.

NASA researchers say rovers bristling with metal whiskers may one day aid the exploration of Mars or other worlds. Such sensors could provide 3-D images of rock textures, steer the rover around hazards or help it function when dust storms cut down on visibility.

Hartmann's work is part of a blossoming effort among robotics experts to take inspiration from animal species that may hold solutions to thorny engineering challenges.

A surprising amount of that animal-based work has come to focus on the humble whisker.

"Rats have been very successful over the course of evolution," said Chris Assad, a robotics researcher at NASA's Jet Propulsion Laboratory. "It would be good for robotics if we could emulate the traits that helped them succeed."

Last month, Hartmann's group published a paper in the journal Nature in which they used a whisker array to build a detailed computerized image of a clay sculpture.

Crafting such machines could help reveal the secrets of how real whiskers operate - a puzzle that has spurred an entire sub-discipline of brain research.

Multitudes of mammal species possess whiskers, from mice to sperm whales, though their uses vary. Seals, which often hunt in dark, murky waters, can use their whiskers to detect wakes left by fish more than 500 feet away.

For Hartmann, a mechanical and biomedical engineer who has dreamed of studying the brain since childhood, building robotic whiskers is a way to understand nature's whisker system from the bottom up.

The group's biggest challenge has been figuring out how whiskers can give detailed information about an object even as they slip and slide around its surface.

The answer, Hartmann and graduate assistant Joseph Solomon found, was to build a four-sensor "follicle" at the base of the robot whisker. The follicles sense how much the whiskers bend in each direction as they glide across a surface. That data is then fed into a computer that can generate an image of the object.

One use of such whiskers may be to drag them behind a planetary rover, gathering information about the planet's surface texture. Hartmann's team already has given the Jet Propulsion Laboratory, home of NASA's Mars missions, a primitive prototype of such a rover - really a remote-control toy truck outfitted with whiskers.

Hartmann believes a robotic submarine could use similar instruments to detect subtle differences in water currents.

The Northwestern group is also studying whether its robotic models match how real rat neurons respond to whisker sensations. Some of that work requires taking readings from the brains of living rats as their whiskers are bent. So far it looks as if the artificial and natural systems make sense of the whisker information in similar ways.

To brain scientists, whiskers are a natural vehicle for studying how animals perceive their surroundings.

The findings are important for human biology too, because the brain areas associated with whisker sensation are comparable to the human brain parts that process signals from fingertips.

"The way animals use whiskers is very much like a blind man with a cane," said Dr. Thomas Woolsey, a neuroscientist at Washington University in St. Louis.

In recent decades Woolsey and other researchers have traced in detail the brain pathways that process what an animal's whiskers are feeling.

Rodent brains have barrels of neurons that correspond precisely to individual whiskers. The barrels are even aligned in rows that match how the whiskers look on a rat's cheek.

The network linked to rat whiskers "will probably be the first major brain system where we can fully detail all of the elements involved," Woolsey said.

Jeremy Manier writes for the Chicago Tribune.

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