What a Wonderful World (8 page)

The oldest and most primitive part of our three-pound universe includes the brainstem and the cerebellum, which turn out
to be the main structures in the brain of a reptile. Our ‘reptilian brain’ controls vital automatic functions such as body temperature, breathing, heart rate and balance. Wrapped around the reptilian brain is a structure that developed in the first mammals about 200 million years ago. The main parts of this limbic system are the hippocampus, amygdala and hypothalamus. They record memories of good and bad experiences and so are responsible for emotions. Wrapped around the limbic brain is the largest structure of all, which first became important in primates. This cerebrum, or neocortex, can overrule the knee-jerk responses of the more primitive parts of the brain. It is responsible for language, abstract thought, imagination and consciousness. It has an almost boundless ability to learn new things and it is the seat of our personality. In short, the neocortex is what makes us human.

Actually, there is one more layer wrapped around the reptilian brain, limbic system and neocortex – and that is, of course, the hard bony shell of the skull. ‘Because important things go in a case, you got a plastic sleeve for your comb, a wallet for your money and a skull for your brain,’ observed George Costanza in
Seinfeld
.
16
The skull is actually reinforced by three layers of protective tissue known as the meninges, in between which is a special shock-proof liquid known as cerebrovascular fluid. An infection here causes the potentially fatal inflammation known as meningitis.

The neocortex is divided into two hemispheres, connected by a bundle of nerve fibres called the corpus calossum. In effect, therefore, we have
two
brains. Usually, the left side is better at problem solving, maths and writing while the right side is creative and better at art or music. For reasons that are not completely understood, the left side of the brain controls the
movement of the right side of the body and vice versa. This is why people who suffer a stroke in the left side of their brain lose movement on the right side of their body and vice versa. A stroke is usually caused by a blood clot in the brain that blocks the local blood supply, damaging or destroying nearby brain tissue.

But the wonder of the brain is not in its gross structure but in its microstructure – in its 100 billion or so neurons and 1,000 billion other support cells, which surround the neurons and their axons, providing them with energy and generally keeping them healthy.
17
However, the sheer number of neurons reveals little about the operation of the brain. ‘The liver probably contains 100 million cells,’ says American neuroscientist Gerald D. Fischbach. ‘But 1,000 livers do not add up to a rich inner life.’
18

The key to the brain’s amazing capabilities are the
connections
between its neurons. ‘All that we know, all that we are, comes from the way our neurons are connected,’ says Tim Berners-Lee, inventor of the World Wide Web.
19
A single neuron may posses 10,000 or so dendrites through which it can interact with 10,000 or so other neurons. In total, the brain may contain something like 1,000 trillion connections.

The big question is: how does all this mind-bogglingly complex neuronal circuitry allow us to remember things and to learn things?

The common experience of memory is that we remember things that are important to us and forget things that are no longer important to us. Of course, we all forget the occasional important thing, like where we put down a book we were reading or a shopping
list scrawled on a scrap of paper. But, by and large, we remember and learn things if they are significant to us – that is,
connected to things we already know
. If you hear a new word in French and you already speak French, you are far more likely to remember it than if you do not speak French. If you know how to balance on a skateboard, you will learn how to balance on a surfboard more easily than someone who has never used a skateboard.

In addition to this,
repetition
seems to be important to remember and learn things. Babies learning to speak repeat the same words over and over. Children learn times tables by reciting them over and over again until they are finally drummed into their skulls. People learning the guitar strum the same sequence of chords, hour after hour.

None of this, of course, tells us how the brain’s neuronal circuitry enables us to remember things and learn new skills. But it does hint that two crucial processes in the brain are
making connections with things we already know
and
repetition
.

The things we
already know
are encoded in the pattern of connections between the brain’s 100 billion neurons, just as the knowledge of how to contract a muscle to move away from a stimulus in the four-neuron network mentioned earlier was encoded in the connection between the quartet of neurons. Nobody knows exactly how the pattern encodes complex information. Although it is perfectly possible to point to a bunch of magnetic memory domains in a computer and say, ‘That is storing a 6 or the letter P’, it is not yet possible to point to a bunch of interconnected neurons in the brain and say they are storing the smell of newly baked bread or the knowledge of how to balance on one leg. Nevertheless, all the evidence points to the pattern of connections between neurons being key to what we know.

The connections between neurons are made by dendrites. Dendrites are therefore synonymous with what we know. To remember something or learn a new skill, therefore, something must happen to the dendritic connections between neurons.

Imagine two neurons that are connected – the axon of the first attached to a dendrite of the second. Now imagine that the first neuron starts firing because it is receiving some stimulus – perhaps some sensory information from the outside world. Remember, the dendritic connection between the two neurons represents something we already know.

Now, if the stimulus is repetitive
and
related to what we know – and the neurotransmitters in the synaptic gap between the axon and the dendrite are primed to amplify the electrical signal if it is related – the dendrite strengthens its connection. This can happen in many ways, but one way is for the dendrite to grow a large number of spines that multiply its connection points.

Of course, two neurons connected by a single dendrite can encode only a ridiculously minimal grain of information. However, since all you know is encoded in the totality of dendritic connections in your brain, by strengthening the connections not just between pairs of neurons but the connections between large numbers of neurons, new knowledge is permanently connected to something you already know and a
memory is laid down
. ‘That is what learning is,’ wrote novelist Doris Lessing. ‘You suddenly understand something you’ve understood all your life, but in a new way.’
20

‘Whenever you read a book or have a conversation, the experience causes physical changes in your brain,’ says American science writer George Johnson. ‘It’s a little frightening to think that every time you walk away from an encounter, your brain has been altered, sometimes permanently.’
21

By this process of strengthening connections between neurons, the network that encodes all you know continually changes. But it not only strengthens connections, it makes new connections and it loses some as well. Think of the neural network of the brain as a vast thicket. In places it is growing and in other places it is being pruned back, as connections are lost between neurons that share nothing in common. This is the process of you forgetting.

What the brain can do that nothing else in the known Universe can do is constantly rebuild and rewire itself. ‘The principal activities of brains are making changes in themselves,’ according to Marvin Minsky.
22

As for learning a new skill, it is a very similar process to laying down a memory. Say riding a bike requires using certain muscles. Strengthening of the dendrites that connect to neurons that control such muscles makes it easier and faster to control them. Thus, just as a memory is encoded in a network of neurons, a skill such as riding a bike or reading a book is encoded in a network of neurons. It becomes hard-wired, automatic.

This strengthening and weakening of connections between neurons or the creation of new connections to modify the network is known as neuroplasticity. Even for me to concoct this explanation, neuroplasticity had to occur in my brain. And neuroplasticity had to occur in your brain for you to understand my explanation. (If you did not understand it, no new permanent connections were made and I have left your brain just the way it was before!)

The brain is a computer but it is a remarkable kind of computer. Whereas a silicon-based computer carries out a task according to the program fed to it by a human being, the brain has no external programmer. It is a
self-programming computer
.
A baby is born with a network of neurons and the potential to connect them in a bewilderingly large number of possible ways. The programming of the baby’s brain – the growing of new connections, the strengthening of some connections and the pruning back of many more – is done by its experience of the world, the information flooding in, hour by hour, day by day, through its eyes, ears, nose and skin.

Although it is very hard to see individual neurons forging links with neighbouring neurons, it is perfectly possible to see the brain programming itself at a much coarser level. The technique of functional magnetic resonance imaging (fMRI) reveals areas of the brain that are working when a person is performing a particular task. For instance, when people have been taught to meditate, it has been possible to see new areas of their brains light up in fMRI scans – new programming. Perhaps one of the most famous examples of fMRI research is a study of London taxi drivers. Eleanor Maguire of University College, London, showed how a region of the drivers’ brains – that associated with spatial awareness – was actually larger than in non-taxi drivers.

‘The brain is a muscle. Use it or lose it,’ seems a facile statement. But – apart from the small matter of the brain not being a muscle – the ‘use it or lose it’ mantra encapsulates a deep truth about the brain. Just as exercising with weights encourages physiological processes that grow more muscle cells, the processes of remembering things, learning things and so on, encourages the brain to grow more neuronal connections. And, just as not exercising causes muscles to atrophy, not exercising the brain causes it to weaken or lose altogether many of its existing neuronal connections. Even Charles Darwin, who knew nothing of neurons, realised the truth of ‘use it or lose it’. ‘If I had to live
my life over again, I would have made a rule to read some poetry and listen to some music at least once every week,’ he wrote in his autobiography. ‘For perhaps the parts of my brain now atrophied would thus have been kept active through use.’

Neuroplasticity is the brain’s big secret. Like natural selection in evolution and DNA in genetics, it is an idea so central to understanding the brain that, without it, nothing makes any sense. Neuroplasticity explains how new experiences constantly rewire the brain – the ultimate lump of programmable matter. It explains how the blank slate of a baby’s brain becomes an adult brain. It explains how a stroke victim may recover lost faculties when the task of the afflicted neurons is taken over by neurons in an adjacent area of the brain. Rehabilitation is long and hard because the process of reprogramming is analogous to a child learning skills for the first time.

And neoplasticity persists as long as you live. Your brain will still be able to make new connections even when you are a hundred years old. A centenarian can learn to use a computer – they might not learn as fast as a child but they can do it.

‘The brain boggles the mind,’ says James Watson, co-discoverer of DNA.
23
It remains the last and grandest frontier in biology, the most complex thing we have yet discovered in our Universe. But we have taken the first tentative steps along the road to understanding it. Nevertheless, there is still a long way to go. But is the destination even reachable? ‘If the human brain were so simple that we could understand it, we would be so simple that we couldn’t,’ wrote the American biologist Emerson M. Pugh.
24

Logically, Pugh is correct. The human brain can never completely understand the human brain. It would be like suspending yourself in mid-air by yanking upwards on your shoe laces. However, the brain is not trying to understand the brain.
Many brains
are trying to understand the brain: the combined minds of international scientific community. ‘All the brains are not in one head’, as an Italian proverb puts it.

We are still no closer to answering the question posed at the beginning of this chapter: why is the Universe constructed in such a way that it acquires the ability to become curious about itself? But, if we understand the brain, we shall finally be able to address it. ‘As long as our brain is a mystery,’ said Santiago Ramón y Cajal, the father of neuroscience, ‘the Universe, the reflection of the structure of the brain, will also be a mystery.’