Edexcel GCSE Psychology

How the brain forms before birth

The human brain starts as a flat sheet of cells in the embryo which folds into a hollow tube, the neural tube, within the first month after conception. The front end of the tube swells into three regions, and these become the three main divisions of the brain: the forebrain, the midbrain and the hindbrain. The rest of the tube becomes the spinal cord. Each division goes on to form structures with different jobs, so the order in which they develop and what each one controls explains a good deal about what a newborn baby can and cannot do.

Brain development before birth is mostly a matter of making neurons (nerve cells), moving them to the right place and then connecting them. Many more neurons and connections are made than are kept. After birth, experience decides which connections are used and strengthened, and the ones that are not used are cleared away, a process called pruning. This is why the early years matter so much for learning: the brain is most adaptable when it is building and trimming its connections fastest.

Forebrain

The forebrain is the largest division and develops into the parts of the brain that deal with thinking and feeling. Its outer layer is the cerebral cortex, which is folded so that a large surface area fits inside the skull. The cortex is responsible for conscious thought, language, memory, planning, decision making, voluntary movement and the processing of sensory information. Deeper in the forebrain are the thalamus, which relays sensory signals to the cortex, and the hypothalamus, which controls body temperature, hunger, thirst and the release of hormones.

The forebrain is among the last parts to mature. Its circuits keep developing through childhood and adolescence, and the parts of the cortex used for planning and self-control (the frontal lobes) are still maturing in the early twenties. A newborn therefore has very limited control over its behaviour and relies on reflexes that are controlled lower down in the brain.

Midbrain

The midbrain is a small region between the forebrain and the hindbrain. It passes messages between the two and deals with basic responses to the senses. It is involved in coordinating eye movements, in automatic reactions to sudden sights and sounds (such as turning towards a loud noise), in movement, and in alertness and the sleep-wake cycle. It is well developed at birth, which is why a newborn will turn towards a sound and follow a face or a bright object with its eyes for a short distance.

Hindbrain

The hindbrain sits at the base of the brain, joining it to the spinal cord, and controls the functions needed to stay alive and to move. It includes the cerebellum, the medulla and the pons. Because these functions are needed from the moment of birth, the hindbrain is one of the earliest regions to become active.

Cerebellum

The cerebellum ("little brain") sits at the back of the hindbrain. It controls balance, posture, coordination and fine, precise movement, and it is involved in learning movements until they become automatic. It develops rapidly late in pregnancy and through the first years of life, which fits with the way a baby's movements gradually become smoother: a young infant cannot sit, crawl or walk steadily, and a toddler's steps are still unsteady, whereas a school-aged child can ride a bike or catch a ball. Damage to the cerebellum leaves a person with clumsy, shaky movements and poor balance, although they can still think and speak normally.

Medulla

The medulla (medulla oblongata) is the part of the hindbrain that joins onto the spinal cord. It controls the automatic, life-sustaining functions that a person does not choose to perform: breathing, heart rate, blood pressure, swallowing and reflexes such as coughing, sneezing and vomiting. It starts to form very early in pregnancy, at around the sixth or seventh week, and is already working when the baby is born, which is why a newborn breathes, swallows and keeps its heart beating without having to learn how. Damage to the medulla is usually fatal, because these functions stop.

Comparing the regions

Why the order of development matters

The brain develops from the bottom upwards and from the back to the front. The parts that keep a baby alive (medulla, hindbrain) are working first, then those for movement and the senses, and the parts for complex thought and self-control come last. The same idea explains why a baby's behaviour seems to consist of reflexes and basic needs, and why the abilities described by theories of cognitive development, such as planning and abstract reasoning, appear only when the forebrain has matured enough.

Because the brain is shaped by experience while it is still forming, a rich environment with plenty of interaction, language and play gives the connections more to work with. Severe neglect, poor nutrition, alcohol or toxins in pregnancy and lack of stimulation can all interfere with normal development, which is why these early years are treated as a period when the brain is especially sensitive to what happens to it.