My serious enemy is brain injury. Despite my watery cushion and fortress skull, I can still be slammed around by blows, accidents, falls. I respond in many different ways. I may swell, just as a mashed finger does. But because I am confined in a bony prison, I have no room to swell. Pressure develops. Symptoms range from blackouts to death.

Stroke is major problem. A clot forms in one of my small blood vessels or one of my small arteries weakens and bursts, and part of me starves. Symptoms range from minor mental lapses to total paralysis and death. Little can be done to correct the effects of stroke in some cases.

In others, rehabilitation is possible. Its success will depend on which part and how much of me has been destroyed.

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The brain mappers have at least a rough outline of my primary functioning areas : vision in the rear, hearing on the sides. The most interesting discovery is the pleasure centre. Teach a rat to press a switch that gives a minute electrical prod to the pleasure centre and the animal will press the switch almost continuously preferring the stimulation even to food, given time, it could die of starvation-presumably happily.

I reside, of course, in a well-protected fortress. The skull is about half a centimetre thick at the top, and even thicker at the base. I am bathed in a watery fluid that cushions me from shocks. A blood-brain barrier serves as a gatekeeper letting some things in, denying entrance to others. Thus, it welcomes the glucose I need, but blocks out bacteria and toxic substances. Most painkillers and anaesthetics pass in with ease - but so, unfortunately, do alcohol and hallucinogenic drugs that wildly distort my normal activities. I may even hear a visual image.

Lift a piece of sod from a lawn and note the baffling intertwining of roots. I am something like that - multiplied by millions. Each of my 30 billion nerve cells, or neurons, connects with others - some as many as 60,000 times !! A neuron looks something like a spider attached to a filament. The spider is the cell body, the filament the axon, the legs the dendrites. The legs pick up a signal from adjacent neurons, pass it to the body; the signal is in turn passed along by the filament at speeds up to 340 k.m.p.h. After each signal passes, it takes the filament about 1/2000 of a second to recharge itself chemically. At no point does one of my neurons touch another; signals are passed spark-gap fashion. At each firing one nerve chemically communicates with another.

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In return of taking care of you, I m piggishly demanding. I represent only 2 % of your body weight, I require 20 % of the oxygen you inhales and a fifth of the blood your heart pumps. I am utterly dependent on a constant supply. Let the supply be cut off for a few minutes and I suffer grave damage - paralysis or death may result. I also demand a steady supply of nourishment - glucose. Even in situations of acute starvation, I get first call on any available, for without me you would die.

In many respects, I am like a vast, unexplored continent, with little more known than the rough outlines of the shore. But the researchers who are attempting to map me have come up with some fascinating information. For example, although all pain is felt in me, I myself have no pain sensation even when I am cut. Thus, brain surgery is performed with the patient wide awake, allowing the brain explorers to stimulate specific areas of me electrically and observe the response. If you ever undergoes such surgery, you will be amazed at what can happen. A tickle of electricity in one place and you might see a long-forgotten third grade teacher.

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Compared to me, other wonders of the universe pale into insignificance. I m a one and a half kilo mushroom of gray and white tissue of gelatinous consistency. No computer exists that can duplicate all my myriad functions. My component parts are staggering in number : some 30 billion neurons and 5 to 10 times that number of cells. All this fitted into the crown of a size 7 hat!

People thinks that they hears with their ears, tastes with tongue, feels with fingers. All these things happen inside of me - ears, tongue and fingers merely gather information. I tell them when they are sick, when hungry ; I govern their sex urge, moods, everything. Even when asleep I continue to handle traffic that would swamp all the world’s telephone exchanges. I have thousands of housekeeping chores to perform. Overseeing breathing, for example. Sensors inform me that carbon dioxide is rising in blood and needs more oxygen. I step up the breathing rate - timing the contraction and relaxation of chest muscles.