Early Brain Development
The Developing Brain
You started life as a single cell. Within weeks of conception, a simple tube of neural tissue had formed, and from this beginning every thought you have ever had, every skill you have ever learned, grew. Understanding how the brain builds itself — and what shapes that process — sits at the heart of developmental psychology.
Brain development follows a pattern that moves from the simplest, most essential structures through to the most complex. The brain does not switch on all at once; it assembles itself in layers, with the parts that keep you alive forming first and the parts that allow you to think, reason and create developing last. This ordering is not random — it reflects millions of years of evolution prioritising survival over sophisticated cognition.
Simple Neural Structures in the Womb
In the first weeks after conception the embryo develops a neural tube. This structure closes and begins to swell at one end, forming the basic regions of the brain. By the time a baby is born, these regions have become far more elaborate, but their foundations were laid before the second trimester had even begun.
The brain develops from the bottom upwards and from the inside outwards. The innermost, oldest structures form first; the outer, newer structures form last. Psychologists describe four key regions in the order they typically mature: the brain stem, the thalamus, the cerebellum, and the cortex.
Brain development follows a bottom-up sequence: brain stem (autonomic functions), thalamus (sensory processing), cerebellum (movement coordination) and cortex (higher cognition). Each layer builds on the one below it.
The Brain Stem: Keeping Alive
The brain stem is the most primitive structure, and it develops first. It controls autonomic functions — the processes that keep you alive without you having to think about them. Breathing, heart rate, blood pressure, swallowing and the sleep–wake cycle are all regulated here. A newborn baby’s brain stem is functional from birth, which is why they breathe, cry and sleep even though the rest of their brain is still immature.
The Thalamus: Routing Sensory Information
Above the brain stem sits the thalamus. It matures next and acts as the brain’s central switchboard for sensory processing. Almost all sensory signals — from your eyes, ears, skin and tongue — are routed through the thalamus before reaching the cortex for interpretation. Without a functioning thalamus, even a fully developed cortex could not receive the information it needs to make sense of the world.
This is why newborns respond quickly to touch, sound and light even before they can make sense of what they are experiencing. The thalamus is relaying the signals; it is the cortex — still developing — that will eventually interpret them fully.
The cerebellum sits at the back of the brain below the cortex. It is responsible for coordinating movement and balance. When a child learns to walk, the cerebellum is doing the heavy lifting — gradually building a smooth, coordinated programme of movement from what was initially a stumbling series of adjustments. The cerebellum also plays a role in procedural skills: riding a bike, typing and catching a ball all rely on cerebellar coordination.
The cerebellum continues to develop into early childhood, which is why babies cannot walk immediately after birth. Even in adulthood, damage to the cerebellum causes difficulties with balance and coordination rather than with thinking or memory — confirming how precisely localised its function is.
The Cortex: Thinking and Cognition
The outermost layer of the brain is the cortex. It is the last structure to develop and the one that develops for the longest time — the prefrontal cortex, which handles planning and decision-making, does not fully mature until a person’s mid-twenties. The cortex is responsible for higher-order cognition: language, abstract thinking, problem-solving, creativity and conscious perception.
Because the cortex develops so late and over such a long period, it is the part of the brain most shaped by experience after birth. This has important implications for education: the brain is not a finished product at birth but a work in progress that continues to be built by the experiences a child has.
The cortex is responsible for higher cognition — language, reasoning and problem-solving — and is the last region to mature. Its prolonged development means it is the part of the brain most open to being shaped by learning and experience after birth.
The debate about nature versus nurture asks how much of our development is determined by our genes (nature) and how much by our environment and experiences (nurture). In brain development, both play essential roles.
The nature side of the argument points to the fact that the basic sequence of brain development — brain stem first, cortex last — is the same in all humans. Genes direct the initial construction: which neurons form, how they connect and what functions they serve. This blueprint is inherited.
The nurture side points to the fact that the brain is not a static structure. Neurons that are stimulated by experience form stronger connections (synapses), while those that are not used weaken or disappear — a process called synaptic pruning. Language development offers a clear example: babies are born with the capacity to learn any language, but they will only acquire the specific language(s) they hear around them. The environment shapes which neural pathways are strengthened.
Most psychologists today accept that brain development is an interaction of both nature and nurture. Genes set the parameters; experience fills in the detail. Neither alone can fully explain how the human brain becomes what it is.