Better tie that string around your finger
a little tighter.
It may turn out the reason some people grow increasingly
forgetful as they age is less about how old they are and
more about subtle changes in the way the brain files memories
and makes room for new ones - differences perhaps better
blamed on patterns of cell-to-cell communication than
the number of birthday candles decorating the cake.
A researcher with the McKnight Brain Institute of the
University of Florida has found that rats become forgetful
because a routine part of the memory process falls out
of kilter, no matter their ages.
This change seems to be related to the chemicals necessary
for brain cells to communicate with each other. The
findings, published this month in the online edition
of Neurobiology of Learning and Memory, expand the possibility
that drugs or therapies could be developed to tune up
the brain's memory mechanisms.
"Aging is associated with an increased rate of
forgetting," said Thomas Foster, Ph.D., the Evelyn
F. McKnight chair for brain research in memory loss
at the College of Medicine. "My work indicates
that the problem may be a slight shift in a normal forgetting
mechanism."
Scientists believe a memory forms when communication
increases between brain cells called neurons. During
memory formation, signals jump across narrow gaps between
cells called synapses, and this output becomes increasingly
larger.
But for this activity to efficiently create a memory,
it helps if signaling decreases among less-involved
neurons. It's like quieting other people in the room
so you can have a phone conversation. Scientists call
the process of decreasing the signal at less-involved
synapses "long-term depression," or LTD.
"This is a normal process that helps with the
sculpting of memory," Foster said. "After
all, we do not remember everything in perfect detail
and we would not want to. This same mechanism probably
is used to clear the brain circuits and make them ready
to be used the next day. However, this mechanism in
excess may lead to rapid forgetting as seen during brain
aging."
Foster's lab group used aged and young rats to examine
the relationships between LTD, aging and memory. The
animals were trained to find a hidden platform to climb
out of a pool of water - something they learned quickly
with repetition.
When the researchers examined the animals' neurons
and used a slow, weak electrical signal to make the
synapses less sensitive - an effort to squelch or depress
the cellular communication - he found that the samples
from younger animals and older animals that had the
highest memory scores throughout their lives were more
resistant to the interference. However, aged animals
with impaired memories displayed what was termed as
"robust long-term depression."
Going back to the phone call example, not only did
the rest of the room get quieter, the callers did, too.
The assumption is if a memory is encoded by making synapses
stronger, then memory can be disrupted by something
that weakens those connections.
"When we see someone we know or perhaps even ourselves
becoming more forgetful, we now know that this is not
an inevitable process," Foster said. "Further,
as we begin to understand the mechanisms of memory,
it becomes possible to predict promising targets for
therapeutic strategies aimed at postponing or alleviating
age-related memory impairment."
Foster said it will be important to understand whether
a change in cellular signaling is necessary to enable
new memories to be formed by discarding old ones.
"The basic gist is that information storage requires
a balance between mechanisms that make synapses stronger
and weaker," said Mark F. Bear, Ph.D., director
of the Picower Institute for Learning and Memory at
the Massachusetts Institute of Technology, who was not
involved with the research. "In aging and disease,
if that balance is disrupted to favor LTD, the unchecked
synaptic weakening leads to memory loss. The good news
is we are developing a good understanding of these mechanisms,
and that will help us find ways to protect memory."
