In the newborn period, the baby’s brain weight is basically about 370g, accounting for 1/4 of the adult brain weight, and when it grows to 4 years old, the brain weight can be 4 times that of the newborn, which is basically close to the adult population. The fetal brain begins to develop at about 8 weeks of gestation, and by 16 weeks of gestation the brain begins to have a sulcus and is already relatively obvious. Usually the baby’s cerebral cortex does not complete a more complete differentiation until 3 years after birth. The actual number of neuronal cells in the baby’s brain at birth is already very high, with about 100 billion neurons, which basically has the neurons of an adult. However, the weight of the baby’s brain is different from that of an adult, mainly because the myelination of the nerves in the newborn baby’s brain is not completed and the number of synaptic connections is not sufficient. Therefore, in the 3 years after birth, the myelination of the newborn brain is rapidly completed, the number of brain synapses is increasing at the same time, and the number of synaptic connections per unit volume of human cerebral cortex is also developing rapidly. The number of synaptic connections generally reaches its peak by age 3 and remains there from age 3 to 12. By the age of 14, the brain starts to use the principle of “use in, use out” and, based on the learning experience, some of the more complete and commonly used neural circuits are left behind, while some of the less frequently used neural circuits are eventually eliminated. Therefore, at around 14 years of age, the unused neural circuits in the synaptic connections of the human brain are eliminated. The development of the infant brain is closely related to neuromyelination. As neuromyelination continues to be completed, the brain’s ability to transmit functions relative to the ability to process information will be faster, the differentiation will be more detailed, and the brain will begin to develop in a mature direction.