The sympathetic system develops before the parasympathetic system. The right hemisphere processes visual emotional information, such as an adult caregiver's emotional expressions. Animal studies have demonstrated that a mother's face can trigger the endorphins that are biologically responsible for experiences of pleasure in social interactions. A child's interest in the mother's face also can trigger the activation of the sympathetic nervous system. By sensitively reading the baby's cues, the mother can regulate the baby's heightened arousal.
Skilled parents provide their babies with experiences that balance the levels of excitement.
The quality of parent- child exchanges affects the development of the frontal cortex, which functions to regulate our social and emotional behaviors. During the child's second year, caregivers engage in more active socialization. Adult caregivers limit children's inappropriate and potentially harmful behaviors, often with discouraging words and facial expressions. For instance, if a child sees less excitement in the caregiver's face, the child will experience a sudden decrease of positive emotions. The child's emotional experience reflects a shift from the sympathetic nervous system to the parasympathetic nervous system.