http://www.pnas.org/content/102/27/9673.full

The Learning Brain

1-3A_What_is_Learning_Powerpoint

The Chandos portrait, artist and authenticity unconfirmed. National Portrait Gallery, London.

WHAT IS LEARNING 

Let me introduce you to our brain.  First some brain surgery, we take off the skull and take out the brain.  This brain weigh1-3A_What_is_Learning_Powerpoints 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 our thoughts, our hopes, our fears, are in the neurons in this brain. We price our abilities to do chess and math but it takes a lot 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’re only aware of a very small fraction of all the activity in the brain, so we need to rely on brain imaging techniques to guide us. 

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 cognitivity 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 churn-over, 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 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 arrow heads. 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, you are not the same person you were after an night 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 that you can get from Microsoft. Shakespeare, the great English poet, already knew this. Here is Macbeth lamenting his insomnia:

Sleep that knits up the ravell’d sleeve of care.

The death of each day’s life, sore labour’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.