BILL BRYSON

Explores the awesome wonder of your brain

LONG ago, when I was a junior high school student in America, I remember being taught by a biology teacher that all the chemicals that make up a human body could be bought in a hardware store for $5 or something like that. I remember being astounded at the thought that you could make a slouched and pimply thing such as me for practically nothing.

It was such a spectacularly humbling revelation that it has stayed with me all these years. The question is: was it true? Are we really worth so little?

Many authorities have tried at various times to compute how much it would cost in materials to build a human. Perhaps the most comprehensive attempt of recent years was made by the Royal Society of Chemistry (RSC) when, as part of the 2013 Cambridge Science Festival, it calculated how much it would cost to assemble all the elements necessary to build the actor Benedict Cumberbatch. (Cumberbatch was the guest director of the festival that year and was, conveniently, a typically sized human.)

According to RSC calculations, 59 elements are needed to construct a human being. Six of these – carbon, oxygen, hydrogen, nitrogen, calcium and phosphorus – account for 99.1 per cent of what makes us, but much of the rest is a bit unexpected. Who would have thought that we would be incomplete without some molybdenum inside us, or vanadium, manganese, tin and copper?

Altogether, according to the RSC’s research, the full cost of building a new human being would be a very precise £96,546.79. Labour and VAT would, of course, boost costs further. You would probably be lucky to get a takehome Benedict Cumberbatch for much under £200,000 – not a massive fortune, all things considered, but clearly not the meagre few dollars that my junior high school teacher suggested.

But, of course, it hardly really matters. No matter what you pay, or how carefully you assemble the materials, you are not going to create a human being.

You could call together all the brainiest people who are alive now or have ever lived and endow them with the complete sum of human knowledge and they could not between them make a single living cell, never mind a replicant Benedict Cumberbatch.

That is unquestionably the most astounding thing about us – that we are just a collection of inert components, the same stuff you would find in a pile of dirt. The only thing special about the elements that make you is that they make you. That is the miracle of life. IT’S 80% WATER – THE REST IS FAT AND PROTEIN THE most extraordinary thing in the universe is inside your head. You could travel through every inch of outer space and very possibly nowhere find anything as marvellous and complex and highfunctioning as the three pounds of spongy mass between your ears.

For an object of pure wonder the human brain is extraordinarily unprepossessing. It is, for one thing, 75 to 80 per cent water, with the rest split mostly between fat and protein. Pretty amazing that three such mundane substances can come together in a way that allows us thought and memory and vision and aesthetic appreciation and all the rest.

The great paradox of the brain is that everything you know about the world is provided to you by an organ that has itself never seen that world.

The brain exists in silence and darkness, like a dungeoned prisoner. It has no pain receptors – literally no feelings. It has never felt warm sunshine or a soft breeze.

To your brain, the world is just a stream of electrical pulses, like taps of Morse code. And out of this bare and neutral information it creates for you – quite literally creates – a vibrant, three-dimensional, sensually engaging universe. Your brain is you. Everything else is just plumbing and scaffolding. Just sitting quietly, doing nothing at all, your brain churns through more information in 30 seconds than the Hubble Space Telescope has processed in 30 years. A morsel of cortex one cubic millimetre in size – about the size of a grain of sand – could hold 2,000 terabytes of information, enough to store all the movies ever made, trailers included, or about 1.2 billion copies of an average book. Altogether, the human brain is estimated to hold something in the order of 200 exabytes of information, roughly equal to ‘the entire digital content of today’s world’, according to Nature Neuroscience. If that is not the most extraordinary thing in the universe, then we certainly have some wonders yet to find.

The brain is often depicted as a hungry organ. It makes up just two per cent of our body weight but uses 20 per cent of our energy.

In newborn infants it’s no less than 65 per cent of their energy. That’s partly why babies sleep all the time – their growing brains exhaust them.

But it is also marvellously efficient. Your brain requires only about 400 calories of energy a day – about the same as you get in a blueberry muffin. Try running your laptop for 24 hours on a muffin and see how far you get. A PEANUT-SIZED SECTION CONTROLS YOUR DESTINY AS THE most complex of our organs, the brain – not surprisingly – has more named features and landmarks than any other part of the body, but essentially it divides into three sections.

At the top, literally and figuratively, is the cerebrum, which fills most of the cranial vault and is the part that we normally think of when we think of ‘the brain’. The cerebrum (from the Latin word for ‘brain’) is the seat of all our higher functions.

It is divided into two hemispheres, each of which is principally concerned with one side of the body, but, for reasons unknown, the vast majority of wiring is crossed, so that the right side of the cerebrum controls the left side of the body and vice versa.

Each hemisphere of the cerebrum is further divided into four lobes – frontal, parietal, temporal and occipital – each broadly specialising in certain functions. The frontal lobe is the seat of the higher functions of the brain – reasoning, forethought, problem-solving, emotional control, and so on. It is the

About one person in every eight has an extra, thirteenth pair of ribs A teaspoon of human blood contains about 25 billion red blood cells

The brain has no pain receptors itself, yet it is where all pain is felt

part responsible for personality, for who we are.

Beneath the cerebrum, at the very back of the head about where it meets the nape of the neck, is the cerebellum (Latin for ‘little brain’). Although the cerebellum occupies just ten per cent of the cranial cavity, it has more than half the brain’s neurons, or nerve cells. It has a lot of neurons not because it does a great deal of thinking but because it controls balance and complex movements, and that requires an abundance of wiring.

At the base of the brain, descending from it rather like a lift shaft connecting the brain to the spine and the body beyond, is the oldest part of the brain, the brainstem. It is the seat of our more basic operations: sleeping, breathing, keeping the heart going. The brainstem doesn’t get a lot of attention, but it is so central to our existence that in the United Kingdom, brainstem death is the fundamental measure of deadness in humans.

Scattered through the brain, rather like nuts in a fruitcake, are many smaller structures: hypothalamus, amygdala, hippocampus and others, which collectively are known as the limbic system (from the Latin limbus, meaning peripheral). It’s easy to go a lifetime without hearing a word about any of these components unless they go wrong.

The basal ganglia, for instance, play an important part in movement, language and thought, but it is only when they degenerate and lead to Parkinson’s disease that they normally attract attention to themselves.

The most important component of the limbic system is a little powerhouse called the hypothalamus. Though only the size of a peanut and weighing barely a tenth of an ounce, it controls much of the most important chemistry of the body.

It regulates sexual function, controls hunger and thirst, monitors blood sugar and salts, decides when you need to sleep. It may even play a part in how slowly or rapidly we age. A large measure of your success or failure as a human is dependent on this tiny thing in the middle of your head.

The hippocampus is central to the laying down of memories. (The name comes from the Greek for ‘seahorse’ because of its supposed resemblance to that creature.)

The amygdala (Greek for ‘almond’) specialises in handling intense and stressful emotions – fear, anger, anxiety, phobias of all types. People whose amygdalae are destroyed are left literally fearless, and often cannot even recognise fear in others.

Considering how exhaustively the brain has been studied, and for how long, it is remarkable how much elemental stuff we still don’t know or at least can’t universally agree upon. Like what exactly is consciousness? Or what precisely is a thought?

It is not something you can capture in a jar or smear on a microscopic slide, and yet a thought is clearly a real and definite thing. Thinking is our most vital and miraculous talent, yet in a profound physiological sense we don’t really know what thinking is.

Much the same could be said of memory. We know a good deal about how memories are assembled and how and where they are stored, but not why we keep some and not others. It clearly has little to do with actual value or utility.

ICAN remember the entire starting line-up of the 1964 St Louis Cardinals baseball team – something that has been of no importance to me since 1964 and wasn’t actually very useful then – and yet I cannot recollect the number of my own mobile phone, where I parked my car or any of a great many other things that are unquestionably more urgent and necessary.

So there is a huge amount we have left to learn and many things we may never learn. But equally some of the things we do know are at least as amazing as the things we don’t. Consider how we see – or, to put it slightly more accurately, how the brain tells us what we see. Just look around you now. The eyes send