Eva Crossan asks :-

Does brain weight increase with age?

Jeff Wickens, a neurobiologist at the Okinawa Institute and Science and Technology, Japan, responded.

This is a very interesting and important question. Neurons, the nerve cells in the brain, are non-dividing cells. That means that you cannot grow more neurons from the existing ones. So, the total number of neurons in your brain cannot increase after the neurons have been formed, which in humans occurs when you are still in the uterus.

Recently some ways for new brain cells to appear have been discovered, but this is a very small number, much less than one per cent. But, although the neurons do not multiply your brain does grow throughout childhood. There are many non-neuronal cells in the brain, called glial cells. These are support cells for the neurons and they outnumber them. The glial cells make myelin, a fatty substance that insulates the axon of some neurons. The axon is like a wire. It transmits the electrical output signals from the centre of the neuron to its distant contacts. The myelin insulation increases the propagation velocity of the impulse.

During childhood and adolescence, there is progressive increase in myelenation of the brain, so the brain weight increases (from 350 - 400 g in the newborn to 1,300 - 1,400g in the young child and the adult). The mylelin allows the different parts of the brain to interact on a faster time scale. For example, connections between the brain areas that control the tongue and the brain areas that process language get a higher speed connection. This occurs about the time we learn to talk.

If the infant’s brain grows too quickly or too slowly, there may be something wrong, so babies often have their head circumference measured. After myelination is complete the brain weight gradually decreases with age, as neurons die and are not replaced. Forunately, although the cells of the brain cannot regrow, the surving brain cells show immense plasticity, even into old age.