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Memories reside in different brain cells at different times

by Ruth SoRelle, M.P.H.

Ron L. Davis, Ph.D.

One popular way of describing how the brain stores its memories is comparing it to the computer hard drive. As some people see it, memories are hard-stored in one place in the brain and retrieved from that spot as needed.

It is easy to understand but perhaps too simple an explanation. New research in the Baylor College of Medicine laboratory of Ron L. Davis, Ph.D., professor of molecular and cellular biology, indicates a much more dynamic process, with memories being retrieved from different parts of the brain at different times in the process. Video

In a report last year, Davis and his colleagues described how they actually made a video recording of a memory trace being formed. (A memory trace is a chemical change in tissue that represents the formation of a memory.) In that report, they described training flies to associate an odor with a mild electric shock. They showed that insect's memory was stored in the antennal lobe (where odors are processed). The memory was stored there immediately but it could be retrieved from that site for only five to seven minutes. Read Scientists capture memory trace.

Where memory goes next

Now in a report in the recent issue of the journal Cell, Davis and his colleagues showed that a similar memory trace is formed in a pair of neurons called the dorsal pair medial or DPM neurons 30 minutes after the training and only through the mediation of a gene called, ironically, amnesiac. This memory lasts about two hours.

"The intriguing thing we don't understand is that it occurs only in one branch of the DPM neuron," said Davis. "Our impression now is that maybe what guides the behavior after training in the first few minutes is the antennal lobe. That is the important part that guides behavior for the small window of time after training. The DPM neurons have that role from 30 minutes to two hours."

The finding belies the commonly held precept that a memory is formed in the same way that data are stored in a computer – always in the same place.

"It's not as if we are forming memories that are then being written to a "hard disk" area of the brain, and it's there and recalled from the same location at any time after learning," said Davis. "We now think that different areas of the brain have dominion over small intervals of time after training. One area might have dominion and then another."

Different locations at different times

"Maybe the final output is the same," he said. "But there are different stations along the pathway responsible for guiding that output at different times after the training. There are different locations for memory traces.

"We've known for a long time that all animals have short-term, middle-term and long-term memories. One popular idea is that these are mechanisms in the same cells – neurons in animals. This is a different explanation. Memories are residing in different cells in the brain."

Others who participated in the research include Drs. Dinghui Yu and Anjana Srivatsan, both of BCM, and Scott Waddell and graduate student Alex Keene, of the University of Massachusetts Medical Center.

Funding for this study came from the National Institutes of Health, the Mathers Charitable Trust, the R.P. Doherty-Welch Chair in Science and the Edward Mallinckrodt, Jr., Foundation.

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