Kids’ brains have high plasticity; they absorb volumes of new material effortlessly and adapt flexibly to changing conditions. As they develop and amass patterns of information, brains tend to crystallize. The aging brain has vast stores of knowledge to draw on to solve the problems it encounters, yet has more difficulty coping with unrecognized patterns – the surprises that drive deep learning in younger brains. These ideas represent the top-level typical thinking among cognitive psychologists and neuroscientists about brain plasticity and crystallization. In a Science News article, Laura Sanders reports on the efforts of researchers who have been exploring why brain crystallization occurs, and whether youthful flexibility can be induced in old brains, including associated potential costs and benefits of extreme rigidity and malleability.