Can’t remember something? Try waiting until later in the day.
Researchers identified a gene in mice that seems to influence memory recall at
different times of day and tracked how it causes mice to be more forgetful just
before they normally wake up.
“We may have
identified the first gene in mice specific to memory retrieval,” said Professor
Satoshi Kida from the University of Tokyo Department of Applied Biological
Chemistry.
Every time you
forget something, it could be because you didn’t truly learn it — like the name
of the person you were just introduced to a minute ago; or it could be because
you are not able to recall the information from where it is stored in your
brain — like the lyrics of your favorite song slipping your mind.
Many memory
researchers study how new memories are made. The biology of forgetting is more
complicated to study because of the difficulties of distinguishing between not
knowing and not recalling.
“We designed a
memory test that can differentiate between not learning versus knowing but not
being able to remember,” said Kida.
Researchers
tested the memories of young adult male and female mice. In the “learning,” or
training, phase of the memory tests, researchers allowed mice to explore a new
object for a few minutes.
Later, in the
“recall” phase of the test, researchers observed how long the mice touched the
object when it was reintroduced. Mice spend less time touching objects that
they remember seeing previously. Researchers tested the mice’s recall by
reintroducing the same object at different times of day.
They did the
same experiments with healthy mice and mice without BMAL1, a protein that
regulates the expression of many other genes. BMAL1 normally fluctuates between
low levels just before waking up and high levels before going to sleep.
Mice trained
just before they normally woke up and tested just after they normally went to
sleep did recognize the object.
Mice trained at
the same time — just before they normally woke up — but tested 24 hours later
did not recognize the object.
Healthy mice and
mice without BMAL1 had the same pattern of results, but the mice without BMAL1
were even more forgetful just before they normally woke up. Researchers saw the
same results when they tested mice on recognizing an object or recognizing another
mouse.
Something about
the time of day just before they normally wake up, when BMAL1 levels are
normally low, causes mice to not recall something they definitely learned and
know.
According to
Kida, the memory research community has previously suspected that the body’s
internal, or circadian, clock that is responsible for regulating sleep-wake
cycles also affects learning and memory formation.
“Now we have
evidence that the circadian clocks are regulating memory recall,” said Kida.
Researchers have
traced the role of BMAL1 in memory retrieval to a specific area of the brain
called the hippocampus. Additionally, researchers connected normal BMAL1 to
activation of dopamine receptors and modification of other small signaling
molecules in the brain.
“If we can
identify ways to boost memory retrieval through this BMAL1 pathway, then we can
think about applications to human diseases of memory deficit, like dementia and
Alzheimer’s disease,” said Kida.
However, the
purpose of having memory recall abilities that naturally fluctuate depending on
the time of day remains a mystery.
“We really want
to know what is the evolutionary benefit of having naturally impaired memory
recall at certain times of day,” said Kida.
Journal article: https://www.nature.com/articles/s41467-019-13554-y
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