Brain development is dependent on activity. The sounds your baby hears, the rocking, washing and cuddling she feels, the sights she sees all activate neural circuits in the her brain. Those circuits that get stimulated the most, develop strength. Those that are inactive get pruned away. The pruning helps those that remain to run quickly and more efficiently. The most important way to support this growth is responsive, tuned-in caregiving. When you bring books into the mix, your baby will form positive feelings about books because she associates them with attention from you.