In the mid-2000s, the concept of brain training gained popularity, especially among high-achieving individuals. Brain training is often gamified, such as in Sudoku or Wordle, to encourage people to practice domain-independent cognitive skills. Advocates claimed that by practicing fundamental reasoning, memory, and problem-solving skills, a person can globally improve cognitive function.33 The scientific evidence, however, suggests that these claims are true only locally, meaning that performance improves on only the practiced tasks.28 For example, if people practice memorizing long lists of numbers, then they get better at memorizing long lists of numbers but at no other memory tasks.39