"Scientists have long understood that the hippocampus processes recent memory, but we did not know where the brain housed our oldest memories," explained Dr. Alcino Silva, principal investigator and professor of neurobiology, psychiatry and psychology at the David Geffen School of Medicine at UCLA. "We knew that the hippocampus did not store memories permanently.
"Most people define memory as their collective lifetime experiences," added Silva, a member of the UCLA Brain Research Institute. "These memories color who we are, yet until now, we've been mystified by how the brain saves and retrieves them."
Silva and his colleagues tackled this mystery using three strategies. First, the scientists engineered mice with a mutant form of a gene called kinase II, which eliminates the ability to recall old memories. The animals were trained to recognize a cage, then tested for their memory of the cage at one, three, 18 and 36 days after training.
"We found that the mutant mice recognized the cage for up to three days after training, but their memory of the cage disappeared after 18 and 36 days," observed Silva. "While they possessed short-term recall, they never developed a distant memory of the cage."
Earlier research suggested that the cortex or outer layer of the brain plays a role in the storage and retrieval of old memories. In their second strategy, the UCLA researchers used imaging methods to visually track which regions of a normal mouse's cortex grew active during memory testing.
No part of the cortex lit up when the animal was exposed to the cage one day after training. When the mou
Contact: Elaine Schmidt
University of California - Los Angeles