Rethinking the brain: Studies show it's wired for change
Findings could help minimize effects of aging, strokes
Carl T. Hall, Chronicle Science Writer
Sunday, November 10, 2002
©2002 San Francisco Chronicle.


Orlando -- Hormones can stimulate birth of new nerve cells. Young children can learn two languages as well as they can learn one. Schizophrenia can reshape the physical connections at nerve endings.

Those were among many experimental results presented by brain researchers last week. And as disparate as the findings may seem, they all point in the same direction, highlighting the amazing flexibility and adaptive powers of the human nervous system.

The brain's basic structure may be laid out before birth by our genes, but scientists have come to realize it's a fluid kind of architecture, from the level of single nerve cells all the way up to the vast circuits that underlie thought and memory.

"The brain is hard-wired for change," said Ira Black, a top brain scientist at the Robert Wood Johnson Medical School in Piscataway, N.J., speaking at the annual meeting of the Society of Neuroscience in the shadows of Disney World.

It's called "plasticity" and represents a fundamental rethinking of the brain's inner dynamics. In the magic kingdom of the mind, new brain cells of various types can spring up just about anywhere, lab findings suggest, and wire themselves into functional circuits if conditions are right.

Scientists hope that by understanding what influences brain plasticity, new ways can be found to take advantage of the phenomenon, perhaps to minimize the effects of normal aging and reduce the damage of strokes or spinal cord injuries.

Brain plasticity persists in adulthood, but is especially pronounced early in life.

A study of bilingual babies by Ioulia Kovelman and Laura-Ann Petitto at Dartmouth College suggests that even very young children have no problem picking up a second language, despite long-standing concerns that exposure to multiple languages too early could disrupt the brain's language-learning faculty.

The study tracked children in Quebec who were exposed to French and either English, Russian, Spanish or sign language, in some cases almost from birth. All the early bilingual children hit normal developmental milestones. Not surprisingly, early exposure also produced children who were completely fluent in both languages, more so than kids who learned at school age.

The take-home message, Petitto said, is that the brain can handle just about anything thrown its way, and the more early-language exposure it gets, the better.

"It's not the case that a child exposed to two languages is confused or developmentally language-delayed," she said. "If the brain were not plastic, that's what you'd predict. If the brain was rigidly set for learning one language, then two languages in early life might throw that system off.

"But we see spectacular agility in these children achieving every single milestone, in each of their languages, on the same developmental timetable."

Even the most basic sensory relays in the brain are molded by experience, overturning the traditional notion that such areas as the primary visual cortex -- the first stop for signals from the eyes -- are largely fixed.

Mriganka Sur, a neuroscientist at the Massachusetts Institute of Technology,

reported that rhesus monkeys given rewards for performing a visual task ended up with enhanced tools of visual perception. That enabled the monkeys to do the task better, in this case discriminating the orientation of lines displayed on a computer screen.

For humans, that implies our brains may be rewiring themselves just by looking at something. "Some of these networks can change on the fly in the adult brain, depending on where we have just been with our eyes," Sur explained.

Other scientists reported new evidence that hormonal factors can alter brain systems late in life, like chemical spatulas reshaping the neuronal clay.

The female hormone estrogen, in particular, has many beneficial effects on cognition, and it appears to help protect against the degeneration of normal aging.

The number of vital projections at nerve endings, known as dendritic spines,

increased 36 percent in a study of monkeys given estrogen replacement therapy after their ovaries were removed, according to a study by John Morrison of Mount Sinai School of Medicine in New York.

Less exposure to stress and an active intellectual life may bring similar benefits through other hormonal mechanisms, Morrison said. "The brain is very responsive to these hormones," he said.

Backing him up with early evidence from animal studies, Phyllis Wise of UC Davis reported that estrogen can protect against nerve-cell death in strokes, while Tae Oh of the University of Maryland School of Medicine showed data suggesting estrogen given right after a spinal cord trauma minimized decay in nerve fibers at the site of the injury.

Those could become important therapeutic tools eventually, although estrogen supplementation is controversial. Effects may vary depending on the form of the hormone taken.

While researchers marvel at the brain's adaptive abilities, it's also clear that at times this flexibility can go haywire.

New findings unveiled last week by neuroscientist William Greenough of the University of Illinois suggested that the devastating symptoms of schizophrenia may reflect a pervasive "maladaption" that encompasses many systems within the brain.

Greenough looked at changes in the prefrontal cortex, a part of the forebrain involved in higher-level cognitive function, in 26 postmortem brain samples, including those from 12 people who had suffered chronic hallucinations, disordered thought and other symptoms of schizophrenia.

Results showed the schizophrenics had extensive abnormalities at the nerve endings, including changes in the form of the same threadlike projections that were the focus of Morrison's estrogen study.

The dendritic spines are on the receiving end at the all-important nerve junctions, or synapses, where a signal moves from one nerve cell to another. They are long known to rapidly change their form, extending and retracting in response to stimulation.

An impoverishment of the nerve junctions has been noted before in various disorders, including schizophrenia, but the new study appears to be the first to show such an extensive degree of abnormalities, including changes in the very structure of the synapses.

No one knows the cause. Genetic factors appear to be almost certainly involved. Side effects from a lifetime of anti-psychotic drugs also may contribute to some of the apparent dendritic burnout.

What seems clear, Greenough said, is that the hallmark cognitive disarray of schizophrenia results from "a co-opting of the basic mechanisms the brain uses for storing information."

Whether good or ill, Black said, the newfound appreciation of brain plasticity should force what amounts to a philosophical shift in the age-old debate as to where genetic influences stop and experience kicks in. In the brain, those two elements should be viewed not so much as antagonistic forces but rather collaborators in a dynamic lifelong process, details of which are just starting to be worked out.

"As a species," Black said, "we love polarities, be it nature-nurture, heaven and hell, or more importantly, the New York Yankees and the Boston Red Sox."

Such polarities may never disappear. But the real point emerging from a slew of studies, scientists said, is that the brain cannot be understood without taking into account both its intrinsic capabilities and the full power of experience to shape our mental landscape.

E-mail Carl T. Hall at

©2002 San Francisco Chronicle. Page A - 8

"Those who seek to predict the future... might first look to the past. The past is a mirror -- and those who ignore its sometimes dark reflection, are doomed to repeat it... Will it be those seeking redemption who shall decide the future... or will those driven only by greed and envy shape our destiny? Even a hundred years later, the outcome is still very much in doubt. .." Outer Limits(Heart's Desire)