Smart Thinking

 Brain cells may grow back

            For decades, researchers have thought that the adult brain is like a computer hard-drive that can’t be upgraded but that only gradually deteriorates.

In the past few years, however, a series of studies has found that the brains of humans and higher animals are renewing themselves fairly steadily in several structures.

And a new study to be published Friday shows that new nerve cells are being generated even in the most advanced part of the brains of adult monkeys, and thus robably also in humans, who have basically the same brain structures.

The findings could eventually lead to new treatments for brain diseases and injuries and also how the mind accomplishes such basic functions as problem-solving and learning.

Princeton University psychologists Elizabeth Gould and Charles Gross report in the journal Science that the formation of new neurons takes place in several regions of the cerebral cortex that are crucial to cognitive and perceptual functions.

Finding this process going on in this part of the brain is dramatic, because many scientists still doubted it occurred in an evolutionarily newer, higher part of the brain, even after regeneration had been found in other parts of the system that guide our sense of smell and basic memories.

But it still appeared that the brain relied on relatively stable structures for storing memories, and that memories were formed by changes in connections between various nerve cells within the brain rather than by changes in the cells themselves.

“People thought: ‘If the cerebral cortex is important to memory, how could it change?’ “Gross said.  “In fact, the opposite view is just as plausible:  if memories are formed from experiences, these experiences must produce changes in the brain.”

William Greenough, director of the Neuroscience Program at the University of Illinois’ Beckman Institute, said the study adds greatly to understanding the mechanisms the cortex has available for storing information and repairing itself.

It particularly dashes the notion that most brain development happens from before birth to three years of age and makes it more likely that experiences throughout adolescence and adulthood shape the structure of our brains.

“If what they have shown holds true for all primates, including humans, it means we really need to rewrite the book on brain development and the way that experience can affect the brain”, said Greenough.

The Princeton scientists used chemical tracing techniques to demonstrate the formation of new cells through division and to follow the migration of immature cells to various parts of the cerebral cortex.

Within the cortex, the researchers found new cells being produced in three areas: the prefrontal region, which controls our ability to concentrate and plan for the future; the inferior temporal region, that allows us to recognize familiar objects and faces; and posterior parietal region, that allows us to sort out the location of objects and distances around us.

The migrations of these new cells, which had never been seen before, could help in directing therapeutic replacement cells to desired sites in the brain that have lost functioning cells to diseases like Alzheimer’s and Parkinson’s, or injury from trauma or strokes.

“It shows there are natural mechanisms in the brain that someday might be harnessed from therapeutic purposes to replenish damaged areas of the brain,” said Gould.  The head of Princeton’s brain research team.

The researchers note, though that such practical applications of their discovery are probably years, if not decades, in the future.

Gould and Gross also stress that they don’t know how the new cells work but say the evidence points to several things.  First, creation of new cells wasn’t seen in the part of the cortex that handles the initial, rudimentary phases of visual processing, suggesting that the role of new cells is reserved for higher brain functions.

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