Brain Growth in the First Five Years of Life


All of this learning is accompanied by a huge spurt of brain growth. At birth, a baby’s brain is about one-quarter the volume of an adult brain. The rest of a newborn’s tiny body is not even close to one-quarter of their adult size. If it were, the average newborn in North America would weigh about 40 pounds! Children’s brains continue to grow, and quickly. By 3 years of age, a child’s brain is already more than 80 percent of adult size. By 5 years of age, it’s grown to about 90 percent of adult size. If our bodies grew at this same pace, the average American would be over 5 feet tall by the age of 5. Children’s large brain size is why their heads are so big for their bodies. Over time, the rest of the body slowly grows and catches up with the brain and head.

Inside the brain, and extending throughout the body is a network of cells called neurons. Neurons are the building blocks of the brain. Working together, they form a complex signaling network. You can think of your brain and all of its neurons like your body’s communications team.

  • Axon
    output fiber of a neuron
    Cell body
    the neuron's processing center
    input fibers of a neuron
    Magnetoencephalography (MEG)
    a non-invasive brain imaging technique used to determine which regions of the brain are active
    cells located in the brain and throughout the body that are specialized to communicate messages
    the process of removing excess synapses
    Sensitive period
    a time in development when the brain is especially ready to learn a skill
    connection point between neurons