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Synapse-Shots of Baby

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Scientists Use Magnetic Resonance Images to Learn How Infants' Neural Networks Develop

January 08, 1998|ROBERT LEE HOTZ | TIMES SCIENCE WRITER

Even in a day when a baby's first photograph is most likely to be an ultrasound scan of a fetus, the exotic images of this sleeping baby girl still may be among the most unusual ever taken.

They are natal images that few parents would recognize; nonetheless, they capture the infant's living essence--the bright, fleeting patterns of her brain as she listens and responds to the reassuring lullaby of her mother's voice.

Created by researchers at Memorial Sloan-Kettering Cancer Center in New York, the pictures are functional magnetic resonance images (fMRI) of a baby's brain. The sedated infant--a 15-month-old South American girl with a brain tumor--was being scanned prior to neurosurgery.

Experts said the images are the first direct observation of a constellation of developing neural networks in action, including language, auditory, vision and motor systems.

Perhaps more at home in a scientist's scrapbook, they were taken at a moment in human development when a young mind is in the throes of creation.

Such images are the newest tool available to researchers trying to directly assess the developing brain, augmenting the efforts of a new generation of neuroscientists studying how infants think.

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In the first several years of life, a child's brain has twice as many neurons with twice as many connections between them and is twice as energetic as an adult brain. In these early years, experience is fashioning a mind from the raw material of neurons, glial cells, synapses and genes the way a sculptor finds the form hidden in a block of marble.

In the first years of life, a child generates up to 15,000 connections to each one of its 100 billion brain cells. By age 2, the number of raw synapses surpasses adult levels--only to be ruthlessly pruned to about half that number by puberty.

Until now, researchers have been able to get only the most indirect insights into how a baby's growing brain works.

"Historically, a clear picture of cognitive development during infancy has been very difficult to obtain because, as you can imagine, unlike older children and adults, infants cannot essentially tell us what they know," said psychologist Harlene Hayne at the Center for Neuroscience at the University of Otago in Dunedin, New Zealand. "But gradually, scientists are beginning to use new techniques that do not require either language comprehension or production."

For example, Hayne has taken advantage of every infant's talent for imitation to investigate how the building blocks of memory and learning emerge in the first year of life.

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In research presented recently at a meeting of the Society for Neuroscience, she reported that children as young as 6 months old can learn new behaviors simply by observing the actions of other people for as little as 30 seconds. They can retain those memories for at least a day, she discovered in a study of 385 pre-verbal infants.

In her study, the researchers used hand puppets and other eye-catching toys to engage the infants' attention. The researchers assessed how long the infants could remember what they had seen and how well they could imitate the actions.

As the infant brain grows between the ages 6 and 18 months, she determined, the ability to learn and remember also grows stronger. While 6-month-olds could remember a behavior for as long as a day, 12-month-old babies could remember it for a week and 18-month-olds could remember it for as long as a month. Indeed, by their first birthday, most children are learning one or two new behaviors every day, just watching the people around them.

"In our study, infants acquired information from a wide range of models, including their parents, their siblings, their day-care classmates, the television and in some instances, the family pet," she said.

"From a practical perspective, our findings and those of many other laboratories around the world clearly indicate that social interactions between adults and infants are an essential ingredient for intellectual growth," she said. "This issue will become increasingly important as we begin to improve the quality of child-care programs for infants and toddlers."

The new images produced at Sloan-Kettering reveal for the first time the biological foundations of such emerging learning ability by showing that even at 15 months of age--a time when many children are still struggling to keep their balance and utter their first words--the human brain has already achieved a remarkable maturity.

"It was surprisingly like the adult," said neuroscientist Joy Hirsch, head of Sloan-Kettering's functional magnetic resonance imaging laboratory, who conducted the brain study.

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