34 - What is Long Term Memoryدوره: Coursera – Learning How to Learn / درس 34
34 - What is Long Term Memory
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متن انگلیسی درس
Welcome back to Learning How to Learn.
What would it be like if you couldn’t
learn new things, you would not
be able to remember new people you met,
or remember what you were told?
This actually happened to a famous
patient in the annals of memory
research whose initials were HM.
At the age of 27, HM had an operation for
epilepsy that took out his hippocampus
on both sides of his brain.
The hippocampus has a shape of a seahorse
and is named from the Greek hippos,
meaning horse and kampos,
meaning sea monster.
The operation was a success.
The epilepsy was cured but
the price was steep.
HM could no longer remember new things.
He had become profoundly amnesic.
Curiously, you could have a normal
conversation with HM, but if you left
the room for a few minutes, he could not
remember you or what you had discussed.
In the film Memento,
the character played by Guy Pearce had
this form of amnesia from a concussion.
Note that he tattooed his
body with messages, so
that he would not forget
what he had to do.
HM could learn other things,
like a new motor skill, but
he could not remember having learned it.
There are multiple memory systems for
different types of learning.
From the studying HM and
animals with similar operations,
we have learned that the hippocampus
is important part of a brain system for
learning and memory of facts and events.
Without the hippocampus and its inputs, it
is not possible to store new memories in
the cortex, a process called memory
consolidation that can take many years.
HM could remember things
from his childhood but
he had trouble remembering things that
had occurred in the years just before his
operation, things that had not yet
become fully consolidated.
Something similar happens when
you have a bad concussion but
this usually resolves,
unlike HM who never improved.
Memories are not fixed but
living, breathing parts of your brain
that are changing all of the time.
Whenever you recall a memory, it changes,
a process called, reconsolidation.
It is even possible to
implant false memories,
which are indistinguishable from
real ones by simply suggesting and
imagining, especially in children
who have vivid imaginations.
Here is a summary.
The green process of consolidation takes
the brain state in active memory and
stores it in long term memory by modifying
synapses on the dendrites of neurons.
These long term memories can remain
dormant for a long time until the memory
is retrieved and reinstated, by the red
process, in short term working memory.
The reinstated memory is in a new context,
which can itself be transferred to
long term memory, thereby, altering
the old memory though reconsolidation.
Our memories are intertwined
with each other.
As we learn new things,
our old memories also change.
reconsolidation also occurs during sleep.
This is why it is more effective
to space learning over time,
rather than mass learning all at once.
If you want to study something for
an hour, you will retain it longer if
you spend 10 minutes each month over
a semester than an hour on one day.
In contrast, if you wait until the day
before an exam to cram the material,
you may be able to retrieve for
the next day on the exam but
it will quickly fade from memory.
In addition to neurons,
brains have several types of
supporting cells called glial cells.
The astrocyte is the most abundant
glial cell in the human brain.
Astrocytes provide nutrients to neurons,
maintain extra cellular ion balance, and
are involved with repair following injury.
In this photo of the cortex,
the astrocytes are stained green and
the neurons are blue.
The intricate arms of the astrocytes
wrap around the neurons,
each embracing thousands of synapses.
A recent experiment suggest
that these astrocytes may
also have an important role in learning.
When human astrocytes were put into mouse
brains, the humanized mice learned faster.
Interestingly, when Einstein’s brain was
examined to find out what made him so
the only difference that could be
found was that he had many more
astrocytes than the average human.
Could astrocytes be the key to
understanding human intelligence.
Well, the more we learn about the brain,
the more may we have to rethink learning.
I’m Terry Sejnowski.
Happy learning, until we meet again.
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