When we learn a new skill, we often get feedback on our performance– rewards for good behavior, debriefs from a sports coach, or corrections from a piano teacher while stumbling through our pieces. In general, though, we improve many skills without anyone telling us how we are doing: we know when we’ve made a mistake when we’re practicing a song alone. Our own “internal critic” evaluates and signals our errors, somehow guiding us toward better performance. What in our brains serves the role of..