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Babies’ brains develop through nature and nurture, and most brain development happens after birth – unlike their other organs, which are fully functioning and just need to grow.

Strong connections made in the brain tend to become lasting, and connections that are not used often may fade away.

A secure attachment relationship is a very powerful factor for healthy brain growth, while high levels of the stress hormone cortisol can be harmful to brain development.

A baby’s brain develops through nature and nurture working together. Nature provides the genes that baby inherits from their parents. The brain also gets information from baby’s world to determine how it needs to develop. This is the nurture aspect, and includes baby’s relationships and experiences. The way that genes and experiences unfold and work together will influence how the brain is built.

Babies are born with billions of neurons (brain cells) in place, but most of these aren’t yet connected. While most of the neurons a baby will ever have are in place at birth, the brain continues making connections throughout life.

Connections are made as babies receive information from their experiences. All of this information goes into the brain through the baby’s senses. Everything they see, touch, taste, hear and smell stimulates the wiring of the brain.

As experiences are repeated, the connections between the neurons become stronger. These strong connections tend to be lasting, and occur whether the experiences are positive or negative.

Connections that aren’t used often become fragile and may fade away. For example, a baby who is not often spoken to is likely to have difficulty learning language later on.

Each neuron has a long, tube-like structure called an axon that sends messages to other neurons. Neurons can receive messages from up to 10,000 other neurons. When baby’s experiences are repeated over and over again and the connections strengthen, the axon becomes coated with a white, fatty substance called myelin. Myelin-coated axons send messages much more quickly and efficiently.

Brain growth over the early years is remarkable. At birth, a baby’s brain is about a quarter of the weight of an adult brain. A 1-year-old’s brain weighs about 70% of an adult brain, and by 3 years old the brain is nearly the weight of an adult’s. At this age, the brain has about twice as many connections as an adult brain.

The quality and number of experiences during these first few years ‘hardwire’ the brain. The brain connections that are used most often tend to become enduring, and the connections that are not frequently used may be lost.

Babies are building the brain they need to survive in their particular environment. As we mature, our brains are less sensitive to the experiences we have and are less likely to change. Their early relationships with parents and whānau play a big part in building their brain. The type of care that baby receives and the relationships that baby has with these close people will build either a strong or weak foundation for all future learning, behaviour and health.

When parents respond promptly to their baby’s cries and comfort baby with warmth and care, baby feels safe and loved and learns to trust. Through this kind of care, baby is likely to develop a secure attachment.

It’s important that these connections for a secure attachment are developing within the first 18 months. If a healthy attachment is not formed during this time, babies are likely to have problems in many areas in later life. They may have difficulty developing trust in their relationships, and may have poor social and educational skills.

A secure attachment relationship enhances brain growth, lessens the harmful effects of stress on the brain, and helps babies gradually learn to manage big feelings and emotions. In childhood they are more likely to have successful friendships and good self-esteem and do well at school. A secure attachment relationship builds pathways in the brain that provide a model for healthy relationships throughout life.

Babies who have mostly negative and stressful interactions and experiences with their whānau may release high levels of a stress response hormone called cortisol. Although babies all experience some stress, when cortisol is released too often or for too long, it may interfere with the developing brain.

The stress response may become highly sensitive and babies may end up over-reacting to any possible threat. When the brain is hardwired this way during the early years, it may be more difficult for tamariki to control their anger, to learn and to get along with others.

Parents can help reduce their baby’s stress by comforting them when they’re upset. Cuddling, gentle touching and a soothing voice can reduce the level of cortisol surging through baby’s body.

A strong, loving relationship between baby and parents is a very powerful factor for building a healthy brain and setting baby up for healthy development throughout life.