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People
March 23, 2001

The Record


Inside navigation of the bat

Nobuo Suga, Ph.D., has led groundbreaking studies of neural mechanisms involved in echolocation


 

Nobuo Suga, Ph.D., professor of biology in Arts & Sciences, works in his den-like Monsanto Laboratory office, which is adorned with photographs of bats, Suga's research specialty. At the entrance of Suga's office is a Noren, an ornate denim cloth with a samurai pattern, a traditional Japanese decoration found in many old restaurants and stores. A Japanese post-doctoral student of Suga's presented him with the gift.

Nobuo Suga, Ph.D., professor of biology in Arts & Sciences, surmounted difficult obstacles to become one of the world's leading experts in the auditory system of bats.

Suga's career in neuroscience has made him internationally known for his studies in the neurophysiology of hearing, most notably in bats, but also in porpoises, Amazonian animals and various insects.

Suga and his collaborators have made groundbreaking discoveries in the complex neural mechanisms involved in echolocation. This is the auditory process by which bats send out sound signals and then interpret the reverberating echoes from the signals to navigate, search for food and communicate among themselves.

He has spent decades analyzing the neural process in bats' central auditory systems, including the cerebral cortex, to understand the brain mechanisms for processing the biosonar signals on which about 900 bat species depend for survival. (Twenty percent of all mammalian species are bats.)

His findings might have implications for human neurology as well. One goal would be a better understanding of how the human brain processes speech sounds.

Suga's work has been honored many times, culminating in his 1998 election to membership in the National Academy of Sciences, one of the highest distinctions a scientist or engineer can attain.

From Japan to the University

Suga and his family emerged destitute from post-World War II Japan. Five months before the war's end, allied bombers raided Suga's hometown of Kobe, burning out the city. The Suga family came out unscathed, but Suga's father's printing business was totally destroyed. Nonetheless, the young Suga eventually was able to attend Tokyo Metropolitan University and earned a bachelor's degree in biology in 1958.

Suga said a pivotal point in his career came shortly before he graduated.

"I was traveling by train from the university with my adviser, Dr. Katsuma Dan," Suga said. "He asked, 'What are your plans after graduation?' I told him I wanted to continue with biology. I could think of nothing else that interested me so much. And Dr. Dan, a famous embryologist and son of a baron, said, 'I think you are the first person I know who wants to be a biologist without money.'"

In Japan, Suga explained, biologists traditionally come from wealthy families and don't even need to take a salary. A week later, Dan suggested that Suga write a paper in English about his honors thesis on embryology and visit his good friend, Yasuji Katsuki, M.D., Ph.D., a famous auditory neurophysiologist at Tokyo Medical and Dental University.

"Dr. Dan told me he thought I'd do well in neurophysiology, plus his friend had lots of research grants," Suga laughed heartily. "I visited the professor and was offered a job working on auditory physiology in cats. Dr. Katsuki suggested that I work on hearing in insects for my Ph.D. While I worked with my colleagues on cats and then monkeys, I worked independently on insects."

Suga's family: (from left) daughter Yuko, wife Hiroko, son Ibuki and Nobuo.

Money was never a problem again for Suga. His early work on insect neurophysiology was so successful that he attracted the attention of D.V. Wigglesworth, Ph.D., of Cambridge University, a prominent insect physiologist, and Donald R. Griffin, Ph.D., of Harvard University, a pioneering bat researcher known as the "Father of Echolocation." Wiggles-worth suggested that Suga apply for a fellowship at the British Embassy in Tokyo, whereas Griffin had an NSF research grant to support his research at Harvard.

Ironically, Suga, who traces his fascination for biology to childhood summer projects on insects, a staple food for bats, found himself pulled away from insects to bats, one of their major predators.

"I had the choice of staying at an exciting place without money or going to another exciting place with money," Suga said. He went to Harvard after finishing his dissertation in March 1963.

From Harvard, Suga's career took off in stunning fashion. He made a name for himself in neurophysiology with the publication of several important papers, and two years after landing in the United States, he jumped coasts, landing at UCLA to work with another big name in neurobiology, Theodore H. Bullock, Ph.D. Suga accompanied Bullock to the University of California-San Diego Medical School in 1966 and settled into the heartland in 1969 after an offer from the late Johns Hopkins, Ph.D., then-chair of Washington University's biology department, who knew of him from their days at Harvard.

Discovering parallels

The essence of Suga's breakthroughs at the University involved mapping areas of the bat brain where different kinds of biosonar information are processed. For instance, Suga found that the Doppler shift (velocity) information is processed in one portion of the bat brain, and distance to a target in yet another. He showed that the bat auditory system was remarkably similar to the mammalian visual system, in which form is processed in one part, motion, for instance, in another.

"This was what people found so interesting about our work, that the two systems share the same basic principles for processing sensory signals," Suga said. "From those discoveries, we would hypothesize the basic neural mechanisms for processing complex sounds in mammals, including humans."

In recent years, Suga and his collaborators have made fundamental discoveries in his bat research on plasticity, which deals with changes in the auditory system of the brain in response to stimuli and associative learning. Plasticity is how circuits in the brain organize and reorganize in response to learning and memory, body changes, novel sensory stimuli and damage to the brain. Gaining a fuller understanding of plasticity can help researchers develop strategies and therapies for victims of stroke and other brain damage.

While researchers have learned much about plasticity in the visual and somatosensory (touch) systems, plasticity of the central auditory system had remained less explored. In bats, Suga and his collaborators have found that auditory information moves from the inner ear all the way to the cerebral cortex at the top of the brain. This is the ascending system. Signals also come down from the cerebral cortex to the inner ear, forming multiple feedback loops. This is the descending, or corticofugal, system. It is this system that modulates the signal processing in the ascending system, and it plays a very important role in plasticity.

Suga and his collaborators are churning out results quickly and have recently published a number of key papers with still more due out this year.

"Professor Suga's work is unique and highly honored by his colleagues at Washington University and throughout the world," said Edward S. Macias, executive vice chancellor and dean of Arts & Sciences. "His pioneering work with the auditory system of bats has provided new insights at a time when both the research community and students are highly interested in the brain. His presence on the Arts & Sciences faculty brings great distinction to Washington University."

Suga and his wife, Hiroko, have two children: son Ibuki, who is a pediatrician finishing his residency at the University of New Mexico at Albuquerque, and daughter Yuko, who is an occupational therapist working for St. Louis County.

While Hiroko returns to Japan every other year to visit relatives, her husband visits less often, usually in conjunction with a scientific meeting. Teaching and research are the things that fulfill him.

"I think of research as a kind of hobby," Suga said. "To plan something and find something new is very enjoyable."

Suga became a U.S. citizen in 1993, prompted by an incident at Lambert International Airport where a customs agent couldn't recognize Suga's picture on his green card, issued in 1966. Nationality is not an important thing to him, but the ability to do his research in the United States is.

"If you grow up in the United States, the research hierarchy here is taken for granted," Suga said. "You get the Ph.D., do two years of post-doc work, become an assistant professor and then often by age 30 you head an entire laboratory. Compared to other countries, this is fantastic."

 

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