It can do just that, if you are short of it, because it is the principal fuel of the brain and the brain has very little to spare.

So medical researchers are studying the metabolic rate of glucose in the brain to investigate both normal and pathological brain physiology. By injecting low level radioactive glucose into the blood stream, then scanning sections of the brain, medical researchers can measure how much radioactive glucose is metabolised.

If the brain tissue were uniform, one would then take the average of the readings over the whole brain. But with such a complex and varied organism as the brain the average might be meaningless. Yet one cannot possibly take individual readings from each blood vessel in the brain. So researchers divide the brain tissue into a number of compartments, then average their readings over each separate compartment.

The question arises: how valid are these results?

Dr Mervyn Young is a recently graduated PhD student of Professor Bass in the Mathematics Department at the University of Queensland. He has sought to answer this question by estimating the possible error in the readings due to compartmentalisation.

To do this Mervyn needed a mathematical model of the small blood vessels in the brain, known as capillaries: He modelled the capillaries, as long cylinders running parallel to each other. Using the fact that the surface area of a cylinder is 2pierl, where r is the radius of the capillary and l the length, he reduced the problem to solving a complex system of differential equations. With some calculus he was able to simplify these equations and then conduct a computer analysis of the experimental data.

His results showed that, provided care is teken in the experiments, the errors due to the conventional compartmental model are acceptably low. So medical researchers can continue to use their standard methods with the knowledge that their results are valid.