old research proven correct

July 30, 1985


NEW EVIDENCE POINTS TO GROWTH OF THE BRAIN EVEN LATE IN LIFE
By DANIEL GOLEMAN

EVIDENCE is building that development and growth of the brain go on into old age. It was once thought that the brain was fixed by late childhood, according to innate genetic design.

As long ago as 1911, however, Santiago Ramon y Cajal, a pioneering neurobiologist, proposed that ''cerebral exercise'' could benefit the brain. But a scientific consensus that the brain continues to bloom if properly stimulated by an enriched environment was long in coming.

''Over the last decade, neuroscientists have become impressed by the degree to which the structure and chemistry of the brain is affected by experience,'' said Floyd Bloom, director of the division of neuroscience and endocrinology at the Scripps Clinic and Research Foundation in La Jolla, Calif. The new research seeks to provide a more detailed understanding of that phenomenon.

Investigations at several different laboratories have shown that environmental influences begin while the brain is forming in the fetus and are particularly strong in infancy and early childhood.

Among the most striking new evidence is a report published in a recent issue of Experimental Neurology showing that even in old age the cells of the cerebral cortex respond to an enriched environment by forging new connections to other cells. Marian Diamond, a professor of physiology and anatomy at the University of California at Berkeley, led the team of researchers who did the study.

In Dr. Diamond's study, rats 766 days old - the equivalent in human terms of roughly 75 years - were placed in an enriched environment and lived there until they reached the age of 904 days. For a rat, an impoverished environment is a bare wire cage a foot square with a solitary occupant; an enriched one is a cage a yard square where 12 rats share a variety of toys, such as mazes, ladders and wheels.

The elderly rats, after living in the stimulating environment, showed increased thickening of the cortex. This thickening, other reseach has shown, is a sign that the brain cells have increased in dimension and activity, and that the glial cells that support the brain cells have multiplied accordingly.

The brain cells also showed a lengthening of the tips of their dendrites, the branches that receive messages from other cells. This in-crease in the surface of the dendrites allows for more communication with other cells.

Previous studies have shown that enriched environments changed brain cells in a number of ways, these among them. While the specific effects differ from one region of the brain to another, in general the enriched environment has been generally seen to result in growth in the bodies of nerve cells, an increase in the amount of protein in these cells and an increase in the number or length of dendrites. In more fully developed dendritic spines, a part of the dendrite that receives chemical messages from other brain cells is induced to further growth.

Moreover, as in the new study, the thickness of the cortex was seen to increase, in part because of an increase in the numbers of glial cells needed to support the enlarged neurons. Dr. Diamond's studies on the older rats show that many, but not all, of these effects continue into old age.

These changes, in Dr. Diamond's view, mean that the cells have become more active, forming new connections to other brain cells. One sign of what the increased brain cell activity signifies for intellectual abilities is that the rats in the enriched environment became better at learning how to make their way through a maze. Indeed, Dr. Diamond and other researchers recently examined specimens from Einstein's brain. The tissue samples, from parts of the cortex presumed critical for mathematical skills, seemed to have unusually large numbers of glial cells.

More Neural Flexibility

What does all this mean for the aging brain? ''There is much more neural flexibility in old age than we had imagined,'' said Roger Walsh, a psychiatrist at the University of California medical school at Irvine, who has done research similar to Dr. Diamond's. ''The changes in brain cells have been found in every species investigated to date, including primates. They certainly should occur in humans as well.''

''In my work,'' Dr. Walsh added, ''I've found that an enriched environment in late life can largely compensate for brain cell deficiencies from earlier deprivations.''

''We've been too negative in how we view the human brain,'' Dr. Diamond said in an interview. ''Nerve cells can grow at any age in response to intellectual enrichment of all sorts: travel, crossword puzzles, anything that stimulates the brain with novelty and challenge.''

Still, there seem to be limits to the degree to which the brain can respond to experience. Richard Lerner, in ''On the Nature of Human Plasticity'' (Cambridge University Press), notes, for example, that the impact of environmental enrichment on brain cells seems to diminish with age, although it continues into old age, an effect Dr. Diamond has noted in her research.

The effects of enriched environments on the brain are but part of a larger investigation of the impact of life's experiences on the brain, and the picture is not always positive.

''Brain plasticity can operate for better or for worse,'' said Jeannine Herron, a neuropsychologist at California Neuropsychology Services in San Rafael. Dr. Herron has organized a conference to be held later this month at which Dr. Diamond and other researchers will describe their findings.

Tests on Vision of Kittens

Perhaps the most frequently cited example of how experience - or the lack of it - can have a negative effect on the the brain is the work of David Hubel. Dr. Hubel, who will also speak at the California conference, won a Nobel Prize for his research on the visual cortex.

As part of his research, Dr. Hubel showed that if the eye of a growing kitten is kept shut so that it is deprived of its normal experience, the cells that would ordinarily register what that eye sees will develop abnormally.

The notion that certain experiences go hand in hand with the growth and development of the brain has been demonstrated in other research, as well. For example, Arnold Scheibel, a professor of anatomy and psychiatry at the University of California at Los Angeles, has found that the cells in the speech centers of infants undergo a growth burst, in which they form many new connections to other cells, just at the time the infant is beginning to respond to voices, between 6 and 12 months. Between 12 and 18 months, as the infant begins to grasp that words have meanings, this growth accelerates.

Part of this explosion of growth, Dr. Scheibel proposes, may be primed by the infant's interactions with adults, who stimulate the centers for speech by talking to the infant.

The main changes that occur during this growth in the cells of the speech centers are in the dendritic ensemble, the projecting branches of the cell that spread to send and receive messages from other cells. ''The dendritic projections are like muscle tissue,'' Dr. Scheibel said. ''They grow more the more they're used.''

''Even in adulthood,'' he added, ''if you learn a new language, it's dendritic fireworks.''

Responses to Injury

The brain's ability to adapt to circumstances can also be seen in its response to injury. Patricia Goldman-Rakic, a neuroanatomist at Yale University medical school, is one of many researchers who have shown that brain cells, within limits, can rearrange themselves to compensate for a brain injury.

''The new connections that occur after an injury to the brain show that the brain's anatomy is not rigidly fixed,'' Dr. Goldman-Rakic said in an interview. ''The uninjured cells reroute how they grow and interconnect. This ability is most prominent during infancy, when neurons are still growing. It doesn't go on forever, but we don't yet know precisely at what point in later life the brain no longer can compensate in this way. We need to more fully understand normal brain maturation first.''

Norman Geschwind, a noted neuroanatomist at Harvard medical school who died earlier this year, had been pursuing evidence suggesting that the experiences of a mother can have a lasting effect on the structure of the developing fetus's brain.

In a series of articles published posthumously in the most recent issues of Archives of Neurology, Dr. Geschwind, with Albert Galaburda, a colleague at Harvard Medical School, proposes that the infant brain is shaped in crucial ways by the level of testosterone, a male sex hormone, present in the intrauterine environment at different stages of fetal development.

At crucial points in the growth of the fetus, brain cells are formed and then migrate to the part of the brain ordained by a genetic plan. In certain parts of the brain these patterns of migration can be affected by the presence of sex hormones, particularly testosterone.

Testosterone levels in the fetus can vary with such factors as the amount of psychological stress the mother feels, maternal diet and possibly even the season of the year.

The main effects of testosterone, according to Dr. Geschwind and Dr. Galaburda, are in the areas of the brain that control such skills as speech, spatial abilities and handedness. One of the key effects of testosterone is in determining the side of the brain on which the centers that control such skills will be located.

When the process goes awry, according to the theory, the result can be problems such as dyslexia, on the one hand, or unusual talents, such as mathematical giftedness, on the other.

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