The studies open the way for eavesdropping on one of the central processes in learning and memory, says HHMI investigator Erin M. Schuman. She and Miguel Remondes of the California Institute of Technology published their findings in the October 7, 2004, issue of the journal Nature.

According to Schuman, the finding sheds light on a central question in learning and memory research that concerns the roles of two brain structures, the hippocampus, which is involved in memory formation, and the neocortex, which is associated with higher brain functions.

"There are two key findings required to understand the present work," said Schuman. "First, lesions of the hippocampus prior to training can prevent the formation of some kinds of short-term memory. Second, if one delays the hippocampal lesion to days after training, one can observe that as the delay increases, the memory deficit decreases. These data suggest that the importance of the neocortex as a memory storage site increases with the lifetime of the memory. In addition, there is a clear need for the hippocampus and cortex to talk to one another."

One candidate for the communication conduit is the temporoammonic (TA) projection, "a pathway that we have been chipping away at understanding for years," said Schuman. "We and others had studied the physiology of this very direct connection between the two areas, but no one had directly studied this pathway's importance in learning."

For the experiments, Remondes perfected a technique to make precise electrical lesions of the TA projection in the brains of rats. In the first s
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
6-Oct-2004