34 - What is Long Term Memory

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.

Like consolidation,

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

awesomely creative,

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.