The Brain, Age 0 to Age 100

Abstract

The MRI scan on the next page shows a newborn baby’s brain. Newborns’ brains look completely different from adult brains. They mainly differ in the degree of ‘myelination’ (maturisation) of white matter. The neural pathways in the white matter myelinate in the first two years of life. What this means is that a fatty layer (the so-called myelin sheath) will grow and cover the neural pathways. This fatty layer could be considered a form of insulation. Without this fatty layer, the brain looks rather watery on an MRI scan. The formation of this fatty layer around the neural pathways follows a set pattern. The neural pathways at the centre of the brain will be the first to grow a fatty layer. Over the first two years of life, this fatty layer will spread to the outside of the brain. The neural pathways which provide motor innervation (the motor cortex) already have a fatty layer when we are born.