FEATURES • Fall 2001

 

Nobuo Suga, professor of biology in Arts & Sciences, has spent more than three decades investigating the auditory system of bats. His research on echolocating bats has revealed principles related to the human nervous system. His recent discoveries on bats and plasticity—dealing with changes in the auditory system in response to stimuli and associative learning—might help researchers develop therapies for victims of stroke and other brain damage.

By Tony Fitzpatrick

The bat has been an enduring image and icon in folklore and popular culture. For Nobuo Suga, professor of biology, the bat has been his ticket to eminence, and a possible path toward understanding neural processes in the bat's fellow mammal, Homo sapiens.

Suga, a member of the Washington University faculty since 1969, has concentrated his career in neuroscience and has become 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 objects to navigate, search for food, and communicate among themselves. It is the bat's way of seeing and communicating. Suga 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 (20 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. His 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.

Studying Insects Leads to Bats

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 graduated with a bachelor's degree in biology in 1958.

Suga said a pivotal point in his career came shortly before he graduated from Tokyo Metropolitan University.

"I was traveling by train from the university with my adviser, Dr. Katsuma Dan," Suga recalls. "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.'"

 
Zhongju Xiao, M.D., research associate in biology, has been working in Professor Suga's laboratory for a year and a half. Xiao researches the function of the auditory corticofugal system in the mustached bat.

In Japan, Suga explains, biologists traditionally come from wealthy families and do not even need to take a salary. A week later, Dan suggested that Suga write a paper in English about his honor's thesis on embryology and visit his good friend, Yasuji Katsuki, 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 [Katsuki] had lots of research grants," Suga laughs. "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."

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 of Cambridge University, a prominent insect physiologist, and Donald R. Griffin of Harvard University, a pioneering bat researcher known as the "Father of Echolocation." Wigglesworth suggested that Suga apply for a fellowship at the British Embassy in Tokyo, whereas Griffin had a National Science Foundation 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 says. Suga 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. Then just two years after landing in the United States, he jumped coasts, landing at the University of California at Los Angeles to work with another big name in neurobiology, Ted Bullock. Suga accompanied Bullock to the University of California at San Diego Medical School in 1966, before settling in the Heartland in 1969, following an offer from the late Johns Hopkins, then chair of Washington University's biology department, who knew of him from their days at Harvard.

Applying Bat Research to Human Brains

Suga's breakthroughs at Washington University have 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, 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 says. "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. This system is what 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 published a number of key papers in the recent past with still more due out in 2001.

According to Erik Herzog, assistant professor of biology, Suga's research on echolocating bats has repeatedly revealed previously unknown principles of the nervous system. "His early work on the auditory systems of invertebrates and lower vertebrates helped to establish the field of 'neuroethology,' the study of the neural basis of behavior," says Herzog, whose office is down the hall from Suga's. "At that time, the late 1960s, a neuroethology meeting might have attracted a few hundred scientists. Interest rapidly grew to the point where tens of thousands of neuroscientists now convene at the annual meeting. Suga has consistently provided beautiful discoveries regarding the mechanisms by which sounds are encoded by specific cells in specific brain areas. I loved learning about his work on bat echolocation as a graduate student in neuroscience.

"More recently, Nobuo's lab has shown us that sensory stimulation causes feedback from the cortex to lower brain structures," continues Herzog. "This feedback plays a critical role in improving information processing and perception. Such plasticity in response to experience has become a major theme in modern neuroscience, a theme that makes it clear that our brains are being constantly rewired and updated. Nobuo is a very special scientist—a sort of gentle powerhouse."

"Professor Suga's work is unique and highly honored by his colleagues at Washington University and throughout the world," says 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."

Ralph Quatrano, chair of the biology department, concurs, "Nobuo has always been a very disciplined and dedicated researcher, setting a clear example of how a very focused program can lead to extremely significant contributions. His election to the U.S. National Academy of Sciences a few years ago is in recognition of his talent in original and creative research. We are very proud to have him as a colleague and as an educator of students who attend Washington University."

Tony Fitzpatrick is the senior science editor in the Washington University Office of University Communications.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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