Eight baby development stages are shaped by the rapidly developing brain: (1) gross motor functions, (2) fine motor functions, (3) perception, (4) cognition, (5) verbal communication, (6) social relations, (7) self-regulation and (8) emotions.
The brain changes that shape baby development stages
Babies’ brains change in many ways as a product of biological maturation and external stimuli. These changes are critical for explaining important baby development stages during the first years.
Though the number of neurons remains constant, brain size triples. Neurons grow to connect distant parts of the brain. They form synapses to allow ‘associative learning’, connecting different experiences with one another. They become myelinated (electrically isolated) to speed up information flow.
Sleeping and digestion rely on the brain stem. The stem is the oldest part of the brain, and it regulates all our vital functions. In the early stages, new connections form between the brain stem and the frontal lobe—the youngest part of the brain, which controls higher order processes, including attention and body perception. These new connections help infants develop a stable biological rhythm and control their bowels and bladders.
Shortly after birth, a huge production of synapses takes place in different areas of the brain. This is followed by a pruning, with critical periods for each brain area. Which neural connections are kept depends on a baby’s learning experiences and follows the use it or lose it principle. This is why six-month-olds can discriminate between facial expressions or oral sounds from different cultures really well, but then show perceptual narrowing to adjust to their own environment towards their first birthday.
To function more efficiently, each neuron also needs to become electrically isolated through myelinisation. At this stage, gross motor actions such as crawling, sitting or standing and walking, as well as fine motor actions such as exploring a toy, all require communication between different parts of the brain. This communication speeds up with increasing neural myelinisation, resulting in improved motor coordination.
Eight Baby Development Stages
Baby development in the early years includes rapid changes in different areas. Each area has its own milestones and develops according to its own rules.
To know and to understand how baby development stages in each area build on one another, and how development in different domains is coordinated, is key to helping infants achieve their potential.
The motor development stages include (1) gross motor functions such as head or torso movements, and (2) fine motor functions such as hand and finger movements. Age-related changes in motor skills largely depend on maturation of the brain but also require muscle training and coordination. In general, moving around and manipulating objects allows a baby to explore the environment, indirectly supporting mental development.
The mental development stages start with (3) perception (especially seeing and hearing), followed by (4) cognition. Cognition includes basic processes (attention, categorization, memory) and higher-order abilities (reasoning and problem solving). Brain maturation and external experiences jointly determine mental development. Mental development induces changes in many other domains.
Later stages of development involve behaviors directed at others, including (5) verbal communication (i.e., language comprehension and production) and (6) building social relations (i.e., forming and maintaining contact, showing prosocial behavior, following rules, cooperating, playing). Adequate stimulation by caregivers largely determines the baby’s development in these domains, but self-directed behaviors seem relevant, too.
Self-directed developments lie behind infants’ (7) self-regulation (e.g., sleeping behavior, bladder and bowel or impulse control) and (8) emotions (experience and expression). Even though progress in these areas has a strong biological basis, co-regulation—-when caregivers help the child regulate his or her internal states—seems equally important. Other- and self-directed abilities are closely intertwined at this stage of development because language skills and social relations both help the child gain an awareness of inner states and control expressive behavior.