In recent years neurobiology has not just thought, but found the unthinkable: new neurones, in the learning-and-memory brain region (the ?dentate gyrus?) of adult mammals, including humans. So what are these cells doing there? Now two reports in Nature Neuroscience (March 1999) give some intriguing hints as to possible answers to this question.
By studying adult male rats trained on four different learning tasks, Elizabeth Gould of Princeton University, New Jersey and colleagues found that neuronal survival appears to depend upon which brain area is used. Twice as many new neurons survived, they discovered, in animals that had learned a task requiring their motivation centre, the hippocampus, than in the animals whose tasks were hippocampus-independent. Indicating, the researchers say, ?that adult-generated hippocampal neurons are specifically affected by and potentially involved in, associative-memory formation.? Fred Gage of the Salk Institute for Biological Sciences, La Jolla, California and colleagues on the other hand, explored the responses of neurons in the dentate gyrus of adult female mice to a variety of experiences. Their work revealed that running enhances neuronal proliferation, and to a lesser extent survival and that the survival of new neurones was also improved in mice that were housed in a mentally stimulating environment. However, unlike Gould?s team, Gage?s group found that navigating a water maze (a hippocampal task) produced no effect at all.
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