Acetylcholine broadcasts widely throughout the brain, and as a result it can trigger changes with any kind of relevant stimulus, whether a musical note, a texture, or a verbal accolade. It is a universal mechanism for saying this is important—get better at detecting this.23 It marks relevance by increasing territory.

You can probably get close to understanding it by considering other situations in which your awareness and plasticity are firing on all cylinders. When you’re an alert traveler in a new land, you drink in the sights of the foreign country, experiencing more novelty, more learning, and more distributed attention. After all, at home you pay attention

Recall Fred Williams, who (unlike Serena and Venus) hates tennis. Why doesn’t his brain change, even after the same number of hours of practice? Because these neuromodulatory systems are not engaged. As he drills backhands over and over, he’s like the rats grabbing the pellets without the acetylcholine.

At some point we might perhaps be able to read the rough details of someone’s life—what he did and what was important to him—from the exact molding of his neural resources. If feasible, this would amount to a new kind of science. By looking at how the brain shaped itself, could we know what a person was exposed to, and perhaps what he cared about?

Imagine you could swallow a capsule that would renew your brain plasticity: this would give you the capacity to reprogram your neural networks to learn new languages rapidly and adopt new accents and new views of physics. The cost is that you’d forget what came before. Your memories of your childhood would be erased and overwritten. Your first love

In contrast, baby brains modify across vast territories.

At the TED conference in 2015, Scott Novich and I algorithmically tracked all the tweets with the hashtag “TED.” On the fly, we aggregated the hundreds of tweets and pushed them through a sentiment analysis program. In this way, we could use a large dictionary of words to classify which tweets were positive (“awesome,” “inspiring,” and so on) and w

This is the powerful difference between just in case information (learning a collection of facts just in case you ever need to know them) and just in time information (receiving information the moment you seek the answer).

Tossing facts at an unengaged student is like throwing pebbles to dent a stone wall. It’s like trying to get Fred Williams to absorb tennis.