- The weight of the average human brain triples between birth and adulthood - reaching a final weight of about 1.4kg (3lb) for men and 1.3kg (2.9lb) for women. By the age of 50, though it shrinks slightly, losing about 30g (a little more than an ounce).
- There is no correlation between brain size and intelligence. A man's brain is usually slightly larger than a woman's, but in both sexes the brain makes up a similar proportion of total body weight.
- Two writers hold opposite records for brain size. The brain of the Russian author Ivan Turgenev (1813 - 1883) weighed 2.012kg (4.44lb). The brain of the French writer Anatole France (1844 - 1924) weighed little more than half that figure, 1.017kg (2.24lb).
- The brain is divided into two hemispheres, each a mirror image of the the other. The right hemisphere controls the muscles of and receives information from the left half of the body; the left hemisphere monitors and controls the right half of the body.
NB. It is now known that this statement is only true for the body from the neck down.
- In right-handed people - the majority - the left side of the brain is concerned with such skills as reading, writing and talking. The right hemisphere deals with artistic activity and the workings of the imagination. In left-handed people the functions of the two hemispheres may be reversed.
- The average brain contains about 10,000 million neurons - microscopic nerve cells. Each cell has a slender projection called an axon which links it to other parts of the central nervous system. Some axons stretch the length of the spinal cord - making them more than a metre (3.3ft) long and the longest cells in the body. Each neuron is also linked to neighbouring neurons by up to 50,000 connections known as dendrites.
- New information reaching the brain from the senses is stored, analysed and acted upon by means of electrochemical impulses passing from neuron to neuron through the dendrite connections. Quite how complex information is coded into these impulses, or how it is translated back again, is imperfectly understood. But it is known that the brain remains active to some degree round the clock, and that each day it triggers hundreds of millions of impulses - more connections than all the world's telephone systems put together.
- The thumb is so important to human dexterity that a larger proportion of the brain is devoted to controlling it than the whole of the chest and abdomen.
- Nerve impulses to and from the brain traven as fast as some racing cars. The fastest impulses recorded, in experiments carried out in 1966, travelled at 290km/h (180mph). Nerve impulses move slightly more slowly in elderly people; at up to about 240km/h (150mph).
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