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Errors are what change your brain
Why most experiences don't count
The popular claim that every experience changes the brain is false. Reaching out and grabbing a pen changes nothing. Plasticity comes when a baby, or an adult, tries to do something and can't.
Two kinds of practice
There are two kinds of practice. Drilling what is already known aims at a hundred percent performance and reinforces it, the way a great dancer drills moves already mastered. Learning a new language or a new physical or emotional skill takes genuine attempts that fail some of the time. Those failure signals are relayed to the cerebellum, which sends the message to change through networks in the brain.
Adrenaline and rest
The friction felt while trying is adrenaline, and learning needs it: blocking adrenaline and its downstream effects with propranolol blocks learning. After the attempt comes a stop, then a return a day or two later to do it again.
How does an error signal teach the brain?
In the 1990s, Wolfram Schultz recorded dopamine neurons in monkeys and found that they fire when a reward is better than expected and go quiet when it is worse. They barely respond to a reward that arrives exactly as predicted. That response is called a reward prediction error. Machine learning researchers later borrowed the idea for training algorithms.
Where does the fifteen percent figure come from?
A 2019 paper in Nature Communications by Robert Wilson and colleagues, titled The Eighty-Five Percent Rule for Optimal Learning, used computational models to estimate the ideal difficulty. For a wide range of learning algorithms, training is fastest when accuracy sits near 85 percent. Easier tasks leave little to learn from, and harder ones produce mostly noise. The authors tested the prediction on artificial neural networks and tied it to animal learning data.
What did propranolol studies show about memory?
Propranolol is a beta blocker that blocks adrenaline's receptors. In a 1994 study in Nature, Larry Cahill and colleagues gave volunteers either propranolol or a placebo before an emotional story with a violent middle section. Those on propranolol remembered the emotional part worse than the placebo group, while memory for the neutral parts was the same. The study became a landmark in research on adrenaline and memory.
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