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Spare Capacity and Reorganisation

The work of British scientist John Lorber provides a startling example of how the human brain can adapt. His research concerned patients suffering from spina bifida, a congenital condition in which the spinal column of the developing foetus fails to close completely, resulting in symptoms ranging from weak muscles and poor skin sensation to paralysis of the legs and loss of bladder control.

One of the complications that can be associated with spina bifida is a condition known as 'hydrocephalus', an abnormal collection of cerebro-spinal fluid in the brain. With this excess of fluid, the ventricles (the fluid reserves in the brain) expand. This increase in the ventricle size can be damaging to the brain, as the enlarged ventricles can impinge on brain cells and destroy them. Thus, severe cases of hydrocephalus can decrease the amount of brain tissue available, resulting in intellectual and physical disabilities.

Professor Lorber studied 600 spina bifida patients who had the added complication of hydrocephalus. He did brain scans on each of these patients to determine the amount of fluid accumulation, and he then compared these to the scans of normal brains. Based on this comparison, the 600 patients were divided into the following four categories:

1: those with minimally enlarged ventricles

2: ventricle expansion equal to 50-70% of the cranium

3: ventricle expansion equal to 70-90% of the cranium

4: ventricle expansion greater than 90% of the cranium

Looking at the fourth category, it is amazing that anyone survived such a massive insult to the brain, and it is not surprising that some of these people had severe neurological problems. But, as incredible as it may seem, some were functioning quite well. Lorber found that 50 per cent of those in this category had IQ scores of greater than 100! Thus, despite such an enormous loss of brain tissue, these people were still able to function at a normal intellectual level.

In one particularly dramatic case, a university student was referred to Lorber because his head seemed slightly larger than normal. A subsequent brain scan showed a gigantic fluid accumulation instead of a normal 4.5 cm depth of cortical tissue between the ventricles and the outer layer of the cortex, there was only a thin layer of brain tissue measuring barely a millimetre. Despite having such a minute amount of brain available, the student had an IQ of 126, a first-class honours degree in mathematics, and was socially quite normal!

It is little wonder that the article describing Lorber's findings was provocatively titled 'Is your brain really necessary?', for it certainly highlights an almost incredible degree of human brain adaptation?

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