NEW YORK — Dr. Peter Huttenlocher, a pediatric neurologist and neuroscientist whose innovative research counting billions of brain synapses — the microscopic information highways of the mind — revealed that brains develop rapidly in young children and later “prune” themselves as they mature, died Aug. 15 in Chicago. He was 82.
The cause was pneumonia and complications of Parkinson’s disease, said his daughter, Anna.
Dr. Huttenlocher’s findings have influenced education and government policy and parents’ priorities, increasing emphasis on the importance of early education.
Today, parents of infants and toddlers encourage bilingualism or violin lessons at what they hope will be peak synaptic moments, school systems focus more on kindergarten and pre-kindergarten programs, and aging baby boomers download Sudoku apps in an effort to preserve precious neurons.
Dr. Huttenlocher’s research, rooted in work he began in the 1970s on cerebral cortex samples taken from human cadavers, helped establish the brain as an adaptive organism — neural plasticity, as it is called — but one in which the ability to adapt declines with age.
“I stumbled on the whole thing,” he told the Chicago Tribune in 1993. “It was something that nobody expected. It took quite a long time until people began to accept that this really happens.”
Dr. Huttenlocher’s work is “like the Bible in this area of science,” said Dr. Eric Kandel, a professor of brain science at Columbia University who received the Nobel Prize in Physiology or Medicine in 2000.
Dr. Huttenlocher was the chief of pediatric neurology at the University of Chicago in the mid-1970s when he began using an electron microscope to photograph billions of synapses. Then he began counting them. He counted at the lab. He counted at home.
“He had all of these pictures of synapses in our house,” his daughter said.
He had set out to study differences in the brains of people who were intellectually disabled, but decided there might be more to learn by studying the control group, the so-called normal brains.
Through his counting, he established a startling fact: In the first year there is an explosion of synaptic activity. A quarter billion synapses might fire in one area of the brain soon after birth and soar past half a billion in the succeeding months.
But that is followed by a significant decline in synapses by the time the child has become a teenager. There can be increases in activity in other areas of the brain or later in life, but nothing matches the bursts of early childhood.
The reduction of synaptic activity, Dr. Huttenlocher concluded, is the brain pruning itself, refining its wiring as it learns and makes sense of the constant stimuli it processes.
“It’s absolutely essential to have this pruning back,” said Kandel, a longtime friend and colleague of Dr. Huttenlocher’s. “You’re getting rid of connections that are not necessary, not desirable, and that handicap your cognitive intellectual functioning later in life.”
Dr. Huttenlocher also discovered that the brains of some people with intellectual disabilities did not always show typical pruning — and that the shape of their synapses was sometimes abnormal. Those findings have helped drive genetic research into causes of intellectual disability.
“That has been a paradigm shift,” said Dr. Christopher A. Walsh, a professor of pediatrics and neurology at Harvard and chief of genetics at Boston Children’s Hospital.
Peter Richard Huttenlocher was born in Oberlahnstein, Germany. His father, Richard, was a chemist and his mother, Else, was an opera singer. His parents divorced when he was young, and his mother left for the United States after she refused to join the Nazi Party.
When he was 18, he visited her and decided to stay in the United States. He graduated from the University of Buffalo in 1953 and received his medical degree from Harvard in 1957. He then had a fellowship at the National Institutes of Health and spent the following decade at Yale. He moved to the University of Chicago in 1974.
In addition to his daughter, Dr. Huttenlocher leaves his wife of 59 years, the former Janellen Burns, a clinical psychologist at the University of Chicago who has done much of her work in the area of cognitive development; two sons, Carl and Daniel; two brothers, Wolfgang and Goetz; and four grandchildren.
Dr. Huttenlocher remained an active clinician while he did his research, seeing patients at Wyler Children’s Hospital in Chicago, and his scientific work was sometimes rooted in trying to learn more about rare conditions affecting patients. Decades after his work on childhood brain development, he focused on how the brain responds when injured, finding it was capable of adaptive change.