Alzheimer's, Dementia & Mental Health
Drug Stopping Degradation of Pathways to Brain’s
Hippocampus May Delay Alzheimer’s
Study shows the memory of aging senior citizens
fails to record new information; meshes with the old
May 13, 2011 - It's something many seniors just
accept: that the older we get, the more difficulty we have remembering things. We can be introduced to new friends at a party
and will have forgotten their names before the handshakes are over. We
shrug and nervously reassure ourselves that our brains' "hard drives"
are just too full to handle the barrage of new information that comes in
daily.
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Alzheimer's, Dementia & Mental Health |
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According to a Johns Hopkins neuroscientist,
however, the real trouble is that our aging brains are unable to process
this information as "new" because the brain pathways leading to the
hippocampus - the area of the brain that stores memories - become
degraded over time. As a result, our brains cannot accurately "file" new
information (like the names of our new friends), and confusion results.
"Our research uses brain imaging techniques that
investigate both the brain's functional and structural integrity to
demonstrate that age is associated with a reduction in the hippocampus's
ability to do its job, and this is related to the reduced input it is
getting from the rest of the brain," said Michael Yassa, assistant
professor of psychological and brain sciences in Johns Hopkins' Krieger
School of Arts and Sciences.
"As we get older, we are much more susceptible to
'interference' from older memories than we are when we are younger."
In other words, when faced with an experience
similar to what it has encountered before, such as meeting new people,
our brain tends to recall old information it already has stored instead
of filing new information and being able to retrieve that. The result?
You can't remember the names of your new friends immediately, but you
easily recall your old friends.
"Maybe this is also why we tend to reminisce so
much more as we get older: because it is easier to recall old memories
than make new ones," Yassa speculated.
The study appears in the May 9 Early Online edition
of the
Proceedings of the National Academy of Sciences.
Yassa and his team used MRI scans to observe the
brains of 40 healthy young college students and seniors, ages 60 to 80,
while these participants viewed pictures of everyday objects such as
pineapples, test tubes and tractors and classified each - by pressing a
button - as either "indoor" or "outdoor."
The team used three kinds of MRI scans in the
study: structural MRI scans, which detect structural abnormalities;
functional MRI scans, which document how hard various regions of the
brain work during tasks; and diffusion MRIs, which monitor how well
different regions of the brain communicate by tracking the movement of
water molecules along pathways.
Some of the pictures used were similar but not
identical, and others were markedly different. The team used functional
MRI to watch the hippocampus when participants saw items that were
exactly the same or slightly different to ascertain how this region of
the brain classified that item: as familiar or not.
"Pictures had to be very distinct from each other
for an older person's hippocampus to correctly classify them as new. The
more similar the pictures were, the more the older person's hippocampus
struggled to do this. A young person's hippocampus, on the other hand,
treated all of these similar pictures as new," Yassa explained.
Later, the participants viewed a series of
completely new pictures (all different) and again were asked to classify
them as either "indoor" or "outdoor." A few minutes later, the
researchers presented the participants with the new set of pictures and
asked whether each item was "old," "new" or "similar."
"The 'similar' response was the critical response
for us, because it let us know that participants could distinguish
between similar items and knew that they're not identical to the ones
they'd seen before," Yassa said.
"We found that older people tended to have fewer
'similar' responses and more 'old' responses instead, indicating that
they could not distinguish between similar items."
Yassa said that this inability among older adults
to recognize information as "similar" to something they had seen
recently is linked to what is known as the "perforant pathway," which
directs input from the rest of the brain into the hippocampus. The more
degraded the pathway, the less likely the hippocampus is to store
similar memories as distinct from old memories.
"We are now closer to understanding some of the
mechanisms that underlie memory loss with increasing age," Yassa said.
"These results have possible practical ramifications in the treatment of
Alzheimer's disease, because the hippocampus is one of the places that
deteriorate very early in the course of that disease."
The team's next step would be to conduct clinical
trials in early Alzheimer's disease patients using the mechanisms that
they have isolated as a way to measure the efficacy of therapeutic
medications.
"Basically, we will now be able to investigate the
effect of a drug on hippocampal function and pathway integrity," he
said.
"If the drug slows down pathway degradation and
hippocampal dysfunction, it's possible that it could delay the onset of
Alzheimer's by five to 10 years, which may be enough for a large
proportion of older adults to not get the disease at all. This would be
a huge breakthrough in the field."
The study was funded by the National Institute on
Aging.
About Hippocampus
The
hippocampus is a brain structure located inside the medial temporal lobe
of the cerebral cortex, and therefore is part of the telencephalon
(forebrain). It belongs to the limbic system and plays major roles in
short term memory and spatial navigation. Humans and other mammals have
two hippocampi, one in each side of the brain. In rodents, where it has
been studied most extensively, the hippocampus is shaped something like
a banana. In humans it has a curved and convoluted shape that reminded
early anatomists of a seahorse. The name, in fact, derives from the
Greek word for seahorse (Greek: ιππος, hippos = horse, καμπος, kampos =
sea monster).
In Alzheimer's disease the hippocampus is one of
the first regions of the brain to suffer damage; memory problems and
disorientation appear among the first symptoms. Damage to the
hippocampus can also result from oxygen starvation (anoxia),
encephalitis, or medial temporal lobe epilepsy. People with extensive hippocampal damage may experience amnesia, that is, inability to form or
retain new memories.
>>
Read more at Wikipedia
