The discovery reverses a dogma nearly a century old and suggests entirely new ways of explaining how the mind accomplishes its basic functions, from problem solving to learning and memory. Elizabeth Gould and Charles Gross report in the Oct.
That contrast suggests that neurogenesis may play a role in performing higher brain functions.
The discovery reverses a dogma nearly a century old and suggests entirely new ways of explaining how the mind accomplishes its basic functions, from problem solving to learning and memory. Greenough, director of the neuroscience program at the University of Illinois' Beckman Institute.
On the basis of the new findings, it is now conceivable that the introduction of new neurons into the circuitry of the brain may play a role in memory. Scientists have observed neurogenesis in birds and rats for many years, but assumed that as evolution advanced and mental capacities increased, the brain supported less and less neurogenesis.
By the time they reached the neocortex -- a matter of days -- they had developed into mature neurons. The new finding in the cerebral cortex is much more dramatic, the Princeton team believes, because the cortex is the largest and most advanced part of the brain. But the fact that there is neurogenesis in the cognitive and executive portions of the brain opens vast new areas that can be jessage.
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McDonnell Foundation. Such work would fall to other scientists who have expertise in human diseases.
The Gould and Gross discovery also may require neuroscientists to draw a less bold distinction between the brains of humans and other animals, says Fernando Nottebohm of Rockefeller University. In the last year, Gould and her colleagues helped this erosion by proving neurogenesis in the hippocampus of several types of monkeys.
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After the discoveries in the hippocampus, says Gould, most scientists adullt convinced that adult neurogenesis was an anomaly and could not be found in the newer, higher parts of the brain. Within the cerebral cortex, the researchers found neurogenesis in three areas: 1 the prefrontal region, which controls executive decision making and short-term memory; 2 the inferior temporal region, which plays a crucial role in the visual recognition of objects and faces, and 3 the posterior parietal region, which is important for the representation of objects in space.
They believed, for example, that the brain relies on a stable structure for storing memories.
This type mesxage migration, which had never been seen before, may prove useful in guiding therapeutic cells to desired sites in the brain that have lost their functioning neurons through disease or injury. The earliest cells, found in the walls of the ventricles and then migrating toward the cortex, were not yet mature.
The strongly imply that the same process occurs in humans, because monkeys and humans have fundamentally similar brain structures. They injected a chemical tracer into messagf brains of several of the animals a few weeks after the BrdU injections. The cerebral cortex is the most complex region of the brain and is responsible for highest-level decision making and for recognizing and learning about the world.
Interestingly, there was no of neurogenesis in a fourth area, the striate cortex, which handles the initial, and more rudimentary, steps of visual processing. Then, at intervals ranging from two hours to seven weeks, they looked for evidence of the chemical in neurons in the cerebral cortex.
In a final test, the researchers showed that the cells extended axons, the long, thin extensions of neurons that send messages to other neurons. The researchers injected BrdU into rhesus monkeys, whose brain structure is fundamentally similar to that of humans. Virtually all theories of learning and memory hold that memories are formed by modifications at the synapse, which is the transmission junction between neurons.
Gould and Gross, both faculty members in the Department of Psychology, collaborated with graduate student Alison Reeves and research staff member Michael Graziano. In particular, it casts doubt on the notion that the all-important time for brain development is from zero to three years of age, and raises the likelihood that experiences through adolescence and adulthood can affect the physical structure of the brain.
The Princeton scientists found that the new neurons were formed in the lining of the cerebral ventricles, large fluid-filled structures deep in the center of the brain, and then migrated messagee distances to various parts of the cerebral cortex.
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This dogma has gradually eroded in the last decade as evidence accumulated for neurogenesis in several evolutionarily older parts of the brain such as the olfactory system and the hippocampus, which is believed to play role in memory formation. In all cases, there were neurons with BrdU in their DNA, which showed that those cells had to have been formed after the BrdU injection.
Gould and Gross emphasize that any ideas about the functions of the new neurons are highly speculative. The tracer has the property of traveling from the end adulf an axon back to the body of the neuron.
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When cells are exposed to BrdU during cell division, the chemical becomes incorporated into the DNA of newly formed cells. For now, that possibility remains speculative. Elizabeth Gould adulr Charles Gross report in the Oct.
Greenough, of the Beckman Institute, says the study also has major implications for theories about how the brain develops.