Researchers working with rats have found the first
solid evidence that still "sharp" older brains store and
encode memories differently than younger brains.
This discovery is reported by a Johns Hopkins team in
the issue of Nature Neuroscience released online
Nov. 13. Should it prove to apply as well to human brains,
it could lead eventually to the development of new
preventive treatments and therapies based on what healthy
older brains are doing rather than on the less relevant
younger brain model, according to study co-author Michela
Gallagher, chair of the
Department of Psychological and Brain Sciences at the
Krieger School of Arts and Sciences.
"We found that aged rats with preserved cognitive
abilities are not biologically equivalent to young rats in
some of the basic machinery that neurons use to encode and
store information in the brain," said Gallagher, who
collaborated with Alfredo Kirkwood and Sun Seek Min of
Johns Hopkins' Krieger
Mind/Brain Institute and Hey-Kyoung Lee, now of the
University of Maryland, College Park. Lee was a research
associate at the Mind/Brain Institute when the research was
done.
The Gallagher-Kirkwood team compared the brains of
6-month-old rats with those of 2-year-old (considered
"aged") rodents that had performed in the "young" range on
various learning tasks. The aged rats' brains also were
compared with those of older rats that showed declines in
their abilities to learn new things. The researchers were
looking at a key set of nerve cell connections that store
information by modifying the strength of chemical
communications at their synapses. (Synapses are the tiny
gaps between nerve cells where chemicals released by one
cell act upon another.) Synaptic communication is the way
brains register and preserve information to form
memories.
The team found that while the older rats with
compromised cognition had brains that had lost the ability
to adjust the force of those synaptic communications, the
older rats whose memories remained sharp still had that
capacity. Interestingly, the successful older rats also
relied far less than did younger rats on a synaptic
receptor that is linked to a common mechanism for storing
memories, the team learned.
"Instead, successful agers relied more than young rats
on a different mechanism for bringing about synaptic
change," Gallagher said. "This 'switch' could serve the
same purpose — storing memories — but through a
different neurochemical device."
This work was supported by grants to Gallagher and
Kirkwood from the National Institute on Aging at the
National Institutes of Health.