Most of a newborn's body movements are reflex behaviors, meaning they occur instinctively rather than intentionally. For example, if you put your finger in a newborn's mouth, they will instinctively start sucking. Similarly, if their eyes are exposed to bright light, they will tightly shut their eyes. Some reflex behaviors persist for several months, while others disappear within a few weeks.
Some reflex behaviors develop into spontaneous actions. For instance, newborns have a rooting reflex, meaning when you stroke their cheek or lips with your hand, they will turn their head toward your hand. This reflex helps them locate the nipple when breastfeeding. Initially, they may turn their head from side to side searching for the nipple, and after turning toward it, they may slightly rotate their head. However, by around 3 weeks old, they will directly move their head and mouth toward the nipple to begin sucking. Sucking is also an instinctive response that fetuses develop before birth. If you've had ultrasound scans during pregnancy, you might have seen the fetus sucking their fingers. During the first few weeks after birth, babies also exhibit a strong reflex behavior known as the Moro reflex or startle reflex. If a baby's head suddenly changes position or tilts backward, or if they are startled by a loud or sudden noise, they will extend their arms, legs, and neck and then quickly retract their arms to their front. They may also cry loudly. The Moro reflex varies in intensity among different babies and is most common before reaching one month of age, disappearing around 2 months old.
Another interesting reflex behavior is the tonic neck reflex. You may notice that when a child's head turns to one side, the arm on that side extends while the arm on the other side bends, resembling a fencer's stance. However, you may not always observe this behavior as it is less conspicuous and may not manifest when the child is disturbed or crying. This reflex typically disappears when the baby is between 5 to 7 months old.
The Moro reflex and tonic neck reflex should manifest symmetrically on both sides of the body. If you notice differences between the reflex behaviors on one side of the body compared to the other, or if one side appears to be more developed than the other, it's advisable to consult a pediatrician.