Lesson 1 said a thought leaves a trail. That was a placeholder. Here is what the trail is made of, and why it changes what counts as practice.
Your brain holds billions of neurons, roughly the number of stars in the Milky Way. Ten of them laid side by side are as wide as a human hair, though a single one can be longer than your arm.
Oakley’s picture is a small alien. It has one eye, the nucleus. One arm reaching up, the axon. Three legs hanging down, the dendrites. And scattered over the legs, small knobbly toes, the dendritic spines.
Neurons talk by shocking each other. One neuron ripples a signal down its axon, and at the end the signal jumps a tiny gap and sparks a dendritic spine on the next neuron. That gap is the synapse. The spark carries on into the second neuron, down its axon, into a third.
That chain of sparks running through connected neurons is a thought. Not a metaphor for one. It is what a thought physically is.
Neurons that spark each other often become a team. The standard phrase is neurons that fire together, wire together. Oakley calls the result a set of brain-links.
When you first meet an idea, the set is short and weak. A few neurons, small dendritic spines, small synapses, a faint spark. That is the state you were in at the end of the tutorial. The link exists. It just cannot carry any load.
Practice does two separate things to it.
Each synapse gets physically bigger, so its spark is stronger. And more neurons join the team, so there are more synapses. Longer sets of links hold more complex ideas, which is why an expert can think about a whole system at once and a beginner cannot.
The rule runs in reverse too. Neurons that stop firing together stop being wired together, and the connections weaken. Oakley’s image is two friends who drift apart because they no longer talk. A skill you have not used in eight years has not been sitting in storage waiting for you. The structure itself has thinned.
Take the mouse instead of the pinball table. A thought is a mouse running a path through a forest. Each time it runs, the path gets wider and easier to follow. That is what practice does, physically. The pinball trail was a mark left behind; the forest path is worn by use. Same picture, with the part that does the work put back in.
Two things follow.
First, watching and reading move a signal through the chain once. Once is not construction. Firing the link yourself is what builds it, which is why you could describe the tutorial and not do it. Closing the tab and rebuilding those twelve steps from memory is the work.
Second, you cannot get the structure faster by pushing harder in one sitting. Enlarging a synapse is physical work on physical tissue. That takes the time it takes, and no amount of intensity tonight substitutes for it. Lesson 1 asked you to alternate modes; the reason the alternation works is that the material change happens on its own schedule and you cannot stand over it.
That the trails can change at all has a name.
The man who worked most of this out was, at eleven, in jail. Santiago Ramón y Cajal argued with his father, fought his teachers, was thrown out of school repeatedly, and had blown a hole in a neighbour’s gate with a cannon he built himself. He hated maths. He had, by his own account, a poor memory. He liked to draw, which his father considered useless.
In the late 1800s the accepted view was that the brain was one continuous network, spread through the head like a spiderweb. It fit the evidence. Signals moved across the brain far too easily to be jumping between separate cells. Cajal disagreed. He thought neurons were individual cells separated by gaps too small for the microscopes of the day to resolve, and that signals sparked across those gaps. He was right, and he won a Nobel Prize for it. He is the father of modern neuroscience.
He got there with the drawing his father dismissed and the maths he hated. His poor memory was never fixed. The relevant point is not that he tried hard. It is that neuroplasticity is the same mechanism in him as in you, and it does not consult your school record before it starts working.
Source: Barbara Oakley, Terrence Sejnowski & Alistair McConville, Learning How to Learn, Ch. 4
Answer to reveal the explanation. Nothing is scored.
1A signal passes from one neuron to the next. Which way does it go?
The axon is the arm that reaches out and sparks a dendritic spine, one of the toes on the next neuron's legs. The receiving side is the part that physically grows when you practise, so the direction is worth keeping straight.
2You followed a 40-minute tutorial completely and could not write a line an hour later. In terms of brain-links, what was missing?
Understanding as it happens and having a set of brain-links are different things. One pass sparks a few neurons weakly. The link is built by repetition, which is why watching someone else do it never transfers.
3What are the two ways a set of brain-links gets stronger?
Each synapse enlarges so its spark is stronger, and additional neurons join the team so there are more synapses. Both come from practice, and longer sets of links are what let you hold more complex ideas.
4You learned a language well eight years ago and have not spoken it since. What does the mechanism predict?
The rule runs in reverse. Oakley's image is two friends who stop talking. That cuts both ways. The same plasticity that let the links thin is what lets you rebuild them faster than you built them the first time.
5Why does the pinball table from lesson 1 need upgrading to the mouse in the forest?
A trail on a pinball table is a mark left behind. A path through a forest widens because something ran along it, which is the actual mechanism: repetition physically enlarges the structure. Same picture, with the mechanism put back in.