In the initial years after birth, and to a lesser extent throughout life, neuronal connection change based on experience, which is called neuroplasticity. Synapses and chains of neurons that are more active become more efficient at transmitting information, which is called potentiation. Synapses and chains of neurons that are less active become less efficient at transmitting information, which is called depression, or they are removed, which is called pruning. Potentiation, depression, and pruning are all parts of neuroplasticity. The central nervous system has far more neurons and synapses at birth that it needs, and these extras will be removed during development. Central nervous system myelination is also incomplete at birth, and continues during the first years of life.
There are multiple systems to assess if the progress of neurodevelopment is normal. The Denver Neurodevelopmental Assessment is commonly used, which evaluates neural functions in terms of gross motor, fine motor, language, and social domains. One year milestones are particularly useful to remember because many, if not most, of the serious neurodevelopmental disorders will be detectable by this age as delays in reaching these milestones. A few helpful one year milestones include: walking for gross motor, pincer grasp (thumb-finger) for fine motor, one to two words for language, and waving for social.
Head size increases as the brain develops until the bones of the skull fuse together at structures called the cranial sutures; this usually happens between one and two years of age. The soft spot in the back, called the posterior fontanelle, usually closes by one to two months, and the soft spot in the front, called the anterior fontanelle, usually closes by one to two years. The normal head circumference is roughly 35 cm at birth, 45 cm at one year, and 55 cm after closure of the cranial sutures.