Dr. Rita Levi-Montalcini, a Nobel Prize-winning neurologist who discovered critical chemical tools that the body uses to direct cell growth and build nerve networks, opening the way for the study of how those processes can go wrong in diseases like dementia and cancer, died on Sunday at her home in Rome. She was 103.
Her death was announced by Mayor Gianni Alemanno of Rome.
"I don't use these words easily, but her work revolutionized the study of neural development, from how we think about it to how we intervene," said Dr. Gerald D. Fishbach, a neuroscientist and professor emeritus at Columbia.
Scientists had virtually no idea how embryo cells built a latticework of intricate connections to other cells when Dr. Levi-Montalcini began studying chicken embryos in the bedroom of her house in Turin, Italy, during World War II. After years of obsessive study, much of it at Washington University in St. Louis with Dr. Viktor Hamburger, she found a protein that, when released by cells, attracted nerve growth from nearby developing cells.
In the early 1950s, she and Dr. Stanley Cohen, a biochemist also at Washington University, isolated and described the chemical, known as nerve growth factor -- and in the process altered the study of cell growth and development. Scientists soon realized that the protein gave them a new way to study and understand disorders of neural growth, like cancer, or of degeneration, like Alzheimer's disease, and to potentially develop therapies.
In the years after the discovery, Dr. Levi-Montalcini, Dr. Cohen and others described a large family of such growth-promoting agents, each of which worked to regulate the growth of specific cells. One, called epidermal growth factor and discovered by Dr. Cohen, plays a central role in breast cancer; in part by studying its behavior, scientists developed drugs to combat the abnormal growth.
In 1986, Dr. Levi-Montalcini and Dr. Cohen shared the Nobel Prize in Physiology and Medicine for their work.
Dr. Cohen, now an emeritus professor at Vanderbilt University, said Dr. Levi-Montalcini possessed a rare combination of intuition and passion, as well as biological knowledge. "She had this feeling for what was happening biologically," he said. "She was an intuitive observer, and she saw that something was making these nerve connections grow and was determined to find out what it was."
One of four children, Rita Levi-Montalcini was born in Turin on April 22, 1909, to Adamo Levi, an engineer, and Adele Montalcini, a painter, both Italian Jews who traced their roots to the Roman Empire. In keeping with the Victorian customs of the time, Mr. Levi discouraged his three daughters from entering college, fearing that it would interfere with their lives as wives and mothers.
It was not a future that Rita wanted. She had decided to become a doctor and told her father so. "He listened, looking at me with that serious and penetrating gaze of his that caused me such trepidation," she wrote in her autobiography, "In Praise of Imperfection" (1988). He also agreed to support her.
She graduated summa cum laude from the University of Turin medical school in 1936, the same year that Mussolini issued a manifesto barring non-Aryan Italians from having professional careers. She began her research anyway, setting up a small laboratory in her home to study chick embryos, inspired by the work of Dr. Hamburger, a prominent researcher in St. Louis who also worked with the embryos.
During World War II, the family fled Turin for the countryside, and in 1943 the invasion by Germany forced them to Florence. The family returned at the close of the war, in 1945, and Dr. Hamburger soon invited Dr. Levi-Montalcini to work for a year in his lab at Washington University.
She stayed on, becoming an associate professor in 1956 and a full professor in 1958. In 1962, she helped establish the Institute of Cell Biology in Rome and became its first director. She retired from Washington University in 1977, becoming a guest professor and splitting her time between Rome and St. Louis.
Italy honored her in 2001 by making her a senator for life.
An elegant presence, confident and passionate, she was a sought-after speaker until late in life. "At 100, I have a mind that is superior -- thanks to experience -- than when I was 20," she said in 2009.
She never married and had no children. In addition to her autobiography, she was the author or co-author of dozens of research studies and received numerous professional awards, including the National Medal of Science.
"It is imperfection -- not perfection -- that is the end result of the program written into that formidably complex engine that is the human brain," Dr. Levi-Montalcini wrote in her autobiography, "and of the influences exerted upon us by the environment and whoever takes care of us during the long years of our physical, psychological and intellectual development."
This article originally appeared in The New York Times.