Study advances memory theory

Steven Schultz

Princeton NJ -- Scientists have found the first direct evidence to support a new theory of how the brain forms memories, an insight that may lead to novel strategies for treating memory disorders.

In an experiment with rats, neuroscientists Elizabeth Gould of Princeton University and Tracey Shors of Rutgers University showed that the animals could form certain kinds of memories only when their brains were producing a steady influx of new brain cells, or neurons.

The results, published in the March 15 issue of Nature, support the emerging theory that freshly minted neurons -- created throughout adult life -- play a key role in memory formation. This theory is in contrast to the conventional view that memory formation is purely a function of chemical and electrical changes among neurons that exist since birth.

"It is a step toward understanding the mechanisms that underlie certain types of learning," said Gould, a professor of psychology. "Now that we know the new neurons are involved in learning, we can study them to see what unique and important features they have that contribute to this function."

Gould is a leading scientist in proving that the brain produces neurons through adulthood, disproving the long-held belief that the brain never acquires new cells beyond those that formed during early development. Once scientists came to accept the idea of an ever-changing brain structure, the question arose: What do these new cells do?

Gould suspected early on that they might play a role in memory, particularly since one of the brain areas where new neurons are found, the hippocampus, is known to be important for learning and memory. To prove that hunch, Gould and Shors treated rats with a chemical that suppresses new neuron formation. The researchers then tested the rats for a type of memory formation known as trace conditioning, in which the animals learn to associate events separated in time. Rats that had been given the suppressant failed to make such associations. When the researchers stopped administering the suppressant, the rats quickly regained their ability to form memories.

"It appears that the new neurons become involved in memory about a week to two weeks after they are generated, and they are involved in memories normally handled by the hippocampus," said Shors.

It is not clear how the new cells help in memory formation. How do they record memories in conjunction with existing cells? What physical traits allow these cells to make associations that older neurons can not? These are among the questions Gould and colleagues are pursuing in their ongoing research.

A more thorough understanding of how the brain forms memories should help medical researchers tackle disorders that involve memory loss, such as Alzheimer's disease, perhaps by designing treatments that stimulate the production of new neurons.


April 9, 2001
Vol. 90, No. 23
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