It's not just babies who love to be bounced and jiggled, older children and grown-ups love it too (think swings, rollercoasters, bumper cars, bungee jumping, and vibrating water beds). A love of repetitive movement is present in even very small babies because of something called the vestibular system, the part of the brain that senses motion and balance. As a baby grows, her vestibular system matures, helping her to keep her head upright or to stay standing without holding on to a parent's leg.
When a newborn is crying inconsolably, repetitive movement like gentle bouncing or jiggling is sometimes the only thing that will comfort her. This bouncing seems to distract her from her sadness and help her become quiet and alert. It also makes her sleepy. If she is fussing because she is resisting sleep, bouncing can be the best way to soothe her.
Some researchers believe that one of the reasons babies love to be bounced is that the movement itself helps improve a baby's sense of balance and her ability to perceive movement. By stimulating the vestibular system, bouncing may actually help a baby improve gross motor skills like crawling and walking.
Babies love attention, smiles, movement, and human contact. Being bounced by a grown-up often provides all four at the same time. When a baby bounces by herself she can also learn cause and effect. A baby in a jumper, for example, learns that when she bends her legs and pushes off she can make herself soar upward. Of course, take care to only bounce and jiggle your baby gently.
Adapted with permission from "Why Babies Do That: Baffling Baby Behavior Explained," by Jennifer Margulis, published by Willow Creek Press. 2005 by Jennifer Margulis. All rights reserved.