Neurological and Brain Development
The Stages and Sequences of Neurological and Brain Development from Birth to 7 Years Old
To understand the stages of brain development we need to understand how it is made up and the importance of what influences that development, and how vital it all is to the outcome of the growing baby from birth.
Interestingly the brain develops from the bottom areas first; followed by higher, more complex areas. Margot Sunderland refers to the brain in layers: the deepest, oldest reptilian brain that looks after body function; the middle, mammalian brain that deals with emotions, and the most evolutionary recent rational brain that processes these emotions and looks after reasoning, creativity, self awareness, kindness and empathy, fear and rage. Whilst the reptilian and mammalian brains are well developed at birth, they are not well connected with the immature rational brain.
The brain begins to develop just 4 weeks into gestation. Neurons (brain cells) form at an incredible rate and are organised very precisely, but at birth the sophisticated parts of the rational brain are still immature and not fully connected. Every experience sends signals between nerve cells along paths of communication called synapses. During the first 3 years the brain creates billions of these connections based on experience, making this the most crucial time in a human brain’s development. Repeated experience reinforces these pathways, which become ‘hard wired’ regardless of whether the experience is good or bad, so repeated early positive experiences are essential to shape the baby’s intellectual, social and emotional view of the world.
The complex systems for survival are in place in the newborn’s reptilian brain – breathing, sleeping, waking, crying, spatial orientation and movement are already functioning. Taste, touch, smell and hearing are also fully working. Vision however, is not as advanced. Newborn babies can think, are perceptive, ready to learn and can clearly communicate their emotional needs. The so-called five senses are hearing, touch, sight, smell and taste, but there are more. Sometimes called the sixth sense, proprioception is the unconscious, internal awareness of movement by parts of the body in relation to each other, e.g. knowing where our arms are if we move them with our eyes closed. Proprioception relates closely to kinesthesia, our sense of spatial awareness used in hand-eye coordination, which with practice becomes an automatic response. This enables us to concentrate on various aspects of performing a task; for example judging distance, talking, looking around and riding a bike – all at the same time. There is much crossover with all the senses both internally and externally, e.g. seeing an object can trigger senses like taste, smell and sounds. Some people are born with synaesthesia – they can link sensations normally experienced separately, e.g. see numbers in colours, or time as a physical shape, or associate numbers, days of the week etc. with personality.
There are other senses present at birth and theses can also influence brain development. A range or combination of sensations e.g. an ache, stabbing, throbbing or burning, located over a small or large area. These are important warning signal and often linked with emotions and their responses such as fear and grief. Until recently it was thought that a baby felt less pain than an adult. However, newborn babies cannot tell us about their pain and it is difficult to assess their perception of it, but their protective reactions, triggered by the sensation of pain can be measured. A baby’s spinal sensory nerve cells are more sensitive than ours, making their response to any harmful stimulus much greater and more prolonged. These nerve cells are linked to proportionally larger areas of skin and so are triggered over a wider body surface. Therefore, the source of pain cannot be located as precisely as we can, so babies find it difficult to distinguish between harmful pain and a harmless touch, suggesting that a newborn’s spinal cord transmits a different pain signal to the cortex (brain) than ours. But the fact that babies cry with meaningful purpose, their facial expression clearly grimacing and their efforts to pull their body away from the stimulus shows they experience and can communicate their extreme discomfort without words. Pain also changes body chemistry and can be measured in a newborn by increased breathing, raised temperature and heart rate. Persistent pain can impact negatively on brain development.
Other senses such as emotions, movement, pressure, temperature, hunger, thirst, and nausea all have an effect on how we, and newborn babies perceive our world and how to deal with that information. This shows we can influence a baby’s social, emotional and mental wellbeing and future life.
At birth a baby’s brain is about a quarter of the size of an adults. Apart from primitive reflexes they already have some remarkable abilities – they can recognise and turn to familiar voices and sounds, have a preference for human faces, they can focus 23cm (the distance between mothers eye and breast), detect the smell of own mother’s milk, have a full range of emotions and give expressions, also a sweet taste preference, can put fist to mouth to suck, copy facial expressions and can distinguish between hot and cold.
After about 2 weeks the baby’s cerebral cortex (responsible for higher-level motor behaviour and intellectual functioning) develops. The early reflexes start to disappear and are replaced by more mature voluntary actions. By 3 months there is significant growth in the hippocampus, the area responsible for memory, emotions and autonomic nervous system. This enables the baby to recognise those closest to them, experience that they are valued and build trusting and secure attachments. If their needs are continuously not met, babies can become stressed, which has a big impact on how the brain develops. When we feel anxious, threatened or in danger our bodies produce the stress hormone cortisol and this causes physical changes; sweaty palms, rapid or shallow breathing, pounding heart and change in appetite. Increased levels of cortisol gives us energy to respond quickly, by wanting to run away, or calm down when needing to cope with an emergency. This is the ‘fight or flight’ reaction, essential for survival. When cortisol is frequently released, the brain is on continual ‘high alert’ giving a sense the world is a threatening, unsafe place, where no one can be trusted. Babies can experience stress when their needs are not met. They are born not knowing how to handle stress and need help to calm down and self-soothe in order to learn coping strategies. We can help babies by holding them close, gently rocking, talking, singing, using their thumb or a soother, a warm bath or simply laying a hand on them for support – whatever works best for an individual baby. Babies can draw on these skills to help them cope with stressful situations throughout their life.
During the first year the cerebellum triples in size. This coordinates and regulates muscular activity also there is significant growth in the frontal and temporal lobes, which are responsible for language and hearing.
By the second year the brain is three-quarters the size of an adult and has made trillions of synapse connections — double the number that an adult has. Connections are ‘user dependant’ - those that are not used regularly are lost as the brain is continually reorganising itself. This is a normal process, called ‘neural pruning’ and explains why routine and repetition are so important to a young child. Pruning allows more synapses to interconnect and strengthen. This coupled with an increase in myelin enables nerve cells to transmit information quicker and allows more complex brain processes. Higher cognitive abilities mean more self-awareness and aware of own emotions and intentions - everything is now ‘me’. Increase in language skills and greater understanding are now evident.
During the third year the synaptic density in prefrontal cortex is at its peak – 200% of adult level. Children now have a better understanding of cause and effect, and begin to use past experiences to interpret what may happen in the future. Improved networking to all the other areas of the body sees improvement in physical ability in both gross and fine motor skills.
By five years old the brain is close to adult size. Although most basic skills have been learnt the brain is pliable and continues to grow throughout life, folding into itself as it develops deeper folds with time and in response to experiences.