04 - What is Learning

Welcome to learning how to learn.

My name is Terry Sejnowski.

Let me introduce you to your brain.

First, some brain surgery.

We take off the skull and

take out the brain.

This brain weighs three pounds,

but it consumes ten times more

energy by weight than the rest of

the body, a very expensive organ.

It is the most complex device

in the known universe.

All of your thoughts, your hopes, your

fears are in the neurons in this brain.

We prize our abilities to do chess and

math, but

it takes years of practice

to acquire these skills.

And digital computers are much

better at it than we are.

It came as a surprise to discover

that what we do so well and take for

granted, like seeing,

hearing, reaching, running,

are all much more complex

problems than we thought and

way beyond the capability of

the world’s fastest digital computers.

What this illustrates is that we are not

consciously aware of how our brains work.

Brains evolved to help us navigate

complex environments, and

most of the heavy lifting is done

below our level of consciousness.

And we don’t need to know how

it’s done in order to survive.

Psychologists who study the unconscious

mind have found that influences

include thought processes,

memory, emotions and motivation.

We are only aware of a very small fraction

of all of the activity in the brain, so

we need to rely on brain

imaging techniques to guide us.

Here is the activity map of someone’s

brain who was asked to lie still,

at rest, in a brain imaging scanner.

On the left is the side

view of the brain and

on the right is the view from the midline.

The colors indicate brain areas whose

activities were highly correlated,

as shown by the time courses below,

color-coded to the brain areas.

The blue areas are highly active when

the subject interacts with the world, but

turn off in a resting state.

The red-orange areas are most

active in the resting state and

are called the default mode network.

Other brain areas are also more active

when you are resting, and these areas can

be further divided into groups of areas

that have common patterns of activity.

This is a new and

intense area of research, and

it will take time to sort out all

the resting states and their functions.

There are a million billion synapses in

your brain where memories are stored.

The old view of the brain

is that once it matures,

the strengths of synapses can

be adjusted by learning, but

the pattern of connectivity does not

change much unless there is brain damage.

But now we know that brain

connectivity is dynamic and

remains so even after it matures.

With new optical techniques for

imaging single connections between

neurons called synapses, we can see

constant turnover, with new synapses

being formed and others disappearing.

This raises a puzzle.

In the face of so much turnover, how do

memories stay stable over so many years?

This is a picture of one

dendritic branch on a neuron which

receives inputs from other neurons.

The synapses are on the spiny

knobs coming off the dendrite.

On the top,

the dendrite was imaged before learning.

The same dendrite is shown below

after learning and after sleep.

Multiple synapses that are newly formed

together on the same branch

are indicated by the white arrowheads.

You are looking down into

the brain of a live animal.

This is really a fantastic new technique.

Synapses are less than

a micron in diameter.

In comparison, a human hair is

around 20 microns in diameter.

This new technique allows us to see

how learning changes the structure of

the brain with a resolution that is

near the limit of light microscopy.

This illustrates that, intriguingly,

that you are not the same person you were

after a night’s sleep or even a nap.

It is if you went to bed with one

brain and woke up with an upgrade.

This is a better deal than

you can get from Microsoft.

Shakespeare, the great English poet,

already knew this.

Here is Macbeth lamenting his insomnia.

Sleep that knits up the raveled sleeve

of care, the death of each day’s life,

sore labor’s bath, balm of hurt minds,

great nature’s second course,

chief nourisher in life’s feast.

Here Shakespeare is making an analogy

between knitted clothes and

sleep that knits up the loose

threads of experience and

concerns during the day and weaves them

into the tapestry of your life story.

You will learn in this first week how to

take advantage of your unconscious mind,

and also sleep, to make it easier to

learn new things and solve problems.

During the lectures you may ask yourself,

how does the brain do this?

A good place to find out more about your

brain is the website brainfacts.org,

brainfacts, one word, .org.

You will find a wealth of interesting

things about brains and behavior, and

in particular about learning and memory.

I am Terry Sejnowski.

Happy learning until we meet again.