These apparently random remembrances, triggered by a sensory cue representing only a portion of the original memory, appear to be dependent on a particular region of the brainthe CA3 region of the hippocampus, say researchers from Baylor College of Medicine in Houston, collaborating with others from the Massachusetts Institute of Technology in Cambridge, and Hokkaido University School of Medicine in Sapporo Japan. Their findings appear in an article in the Journal Science, available currently (May 30, 2002) at the Science Express web site (www.sciencexpress.org).
It appears that the CA3 region of the hippocampus is essential for the phenomenon called pattern completion, said Dr. Dan Johnston, professor of neuroscience at Baylor College of Medicine. That is the ability to recall memories from partial representations of the original.
The scientists genetically engineered a strain of mice in which a specific protein called the NMDA receptor was absent only in the CA3 region of
the hippocampus. This receptor senses the primary neurotransmitter of the brain, glutamate, in ways thought to be necessary for some forms of learning and memory. When the mutant animals were trained in a maze with several visible cues, they performed the task as well as normal animals. However, when some, but not all of the cues were removed, the mutant animals could not remember where they were supposed to go. The normal animals did fine.
The hippocampus appears to be the place where some memories are initially processed and stored, said Johnston. He believes that those memories can remain there for up to a year before being transferred to other brain regions, sp
Contact: Anissa Anderson
Baylor College of Medicine