Neuroscientist Studies Brains Of Bizarre-Looking Mammals

"I used to be a little defensive about studying such bizarre animals," the assistant professor of biological sciences acknowledges. "But then I realized that what makes these animals so strange is their extreme specialization and, for that very reason, there is a great deal that we can learn from studying them."

Catania's research strategy appears to by paying off. He has just been awarded one of only 15 fellowships given annually by the Searle Foundation, a highly competitive honor that will provide him with $240,000 to use on his research for the next three years. The award follows hard on the heels of having one of his papers selected as the cover article for the April issue of the journal Nature Neuroscience.

An interest in the sense of touch led Catania to the community of moles. In their underground world there is little light, so vision is not very important. Also, sounds are attenuated and hearing is not that valuable either. That leaves the senses of touch and smell pre-eminent.

His first research subject was the star-nosed mole--an animal that looks very much like an ordinary mole except that it has a peculiar star of fleshy appendages ringing its nose. Although they range from Canada, down through the Eastern United States as far as Georgia, people rarely see these unusual-looking creatures because they are the only moles that live in marshes and wetlands. here have been a lot of different ideas about the function of this unusual nose ornament, but it was not until Catania studied this star-shaped proboscis as part of his doctoral thesis at the University of California, San Diego that the star's true function came to light. He established that it is an extraordinary touch organ, covered with more than 25,000 microscopic sensory receptors that allow the hamster-sized mole to literally feel its way around its subterranean environment.

Since coming to Vanderbilt, Catania has determined that the star-shaped nose is connected to the mole's brain by some 100,000 nerve fibers, six times the number that connect the human hand and brain. By studying the development of the mole, he has also established that the nose appendages form in a way that differs from that by which human fingers, insect legs and most other appendages are formed. Instead of following the normal pattern of budding and growing out directly from the body, the mole's distinctive nose rays form as fleshy cylinders on the side of the animal's muzzle before detaching and unfolding forward.

Looking in detail at the neural connections of individual rays of the star, Catania has also found a striking functional parallel between the wiring of the nose star and the way that the eye is organized in sighted animals. Much like the central area of the retina, called the fovea, the two central appendages in the star have more connections to the brain that the outer, or peripheral appendages. Much as a person instinctually looks directly at an object of interest so its image is centered on the fovea, the star-nosed mole moves quickly to touch items of interest with its two central appendages after they are discovered by its peripheral arms. Most recently, the neuroscientist has established that these central appendages owe much of their increased sensitivity to the fact that they are programmed to begin developing earlier than the other appendages in the star.

With Searle Foundation support, Catania plans to extend his studies to the naked mole rat, an animal famous in animal behavior circles because it lives in insect-like colonies organized around single breeding females, or queens. He recently obtained a colony of naked mole rats. These creatures have a much different tactile system than do the star-nosed moles. Instead of putting the vast majority of their touch-sensors in one organ, the mole rat has sensory hairs spread all over its body, including its tail. Mole rats also have an exceptional set of front teeth. They have four incisors that are located entirely outside of their mouth--they close their mouth tightly when they are using their teeth for digging. They also can move each front tooth independently. Fully 30 percent of the mole rat's cortex is devoted to processing information from the region where the teeth are located, Catania says.

NOTE: For additional information, as well as examples of accompanying illustrations, see the article posted on Exploration, Vanderbilt's online research magazine, at http://exploration.vanderbilt.edu/news/news_mammals.htm