Science Spin March 2010

Unravelling the mysterious brain

By Veronica Miller

Billions of electrical impulses are born every millisecond in our brains. These actively motivate our minds, move our limbs and mark us above other mammals on the planet. Yet apart from the odd headache, you may wonder how we know the brain is working and what exactly it does?

Many thousand's of years ago, according to Buddhist and Hindu legends, an Indian sage told a parable about "The blind men and an Elephant". According to the story, a Raja was asked to settle a dispute in his court between the men of Savatti who believed life was eternal and those who did not. The Raja gathered six men of Savatti who were blind and sent them to the jungle to encounter an elephant. They were told to return to the court and describe the elephant to him.

The first blind man laid his hands on the elephant's legs and described the elephant to the Raja as being like a wall. The second man felt the elephant's sharp tusks and told the Raja that the elephant was more like a spear. The third felt the elephant's trunk and said that the elephant was snake-like. The fourth felt the elephant's wrinkly knees and said it was like a tree; and the fifth laid his hands on the elephant's large flat ears and said it was like a fan. The sixth and final man touched only the elephant's tail and told the Raja he had encountered a rope.

For many hours the six men argued with each other, each convinced that they and only they were right as to what an elephant truly was. In the end no resolution was found, as none of the men knew what the elephant was like. Not one had seen the whole elephant.

You might like to think of the brain as being like the elephant from the parable. Aside from the fact that both elephants and brains are large rubbery and grey coloured, the brain is also something that makes blind men of many who study it

If you were the Raja then the six blind people you send to study the brain would be a neurosurgeon, neuroscientist, neuropathologist, neurologist, psychiatrist and psychologist. And perhaps somebody with a map to help them find their way back to your palace to tell what they found.

INSIDE

One of the simplest ways to find out what is happening in somebody's head is to cut it open and take a look inside. Once you do that, and see the quivering electrostatic mass of grey tissue inside the skull, the next stage is to find out what the different bits do. By studying people with brain injuries, and by removing parts of people's brains, primitive neurosurgeons learned the location and function of different brain parts. Nowadays, the blind neurosurgeon, equipped with the latest technology, could tell you from trial, error and immense learning what the brain is made of and what function different parts hold.

With an insatiable desire for information and an ability not to believe most of what they read, the neuroscientist will attempt to study how the brain works. He or she, will use information from physiology about the brain's wiring, biochemistry about the types of nutrients it needs, cytology about the cells that make up the brain, and genetics and anthropology about the brain's development, to distill information for you to sip on.

Equipped with scientific information the neurologist will try to understand what happens when our brains don't work.

Years ago the neurologist might have been the witch doctor or sooth sayer in the village who had a magic herb garden and an ability to make aspirin from forest foliage. Nowadays thanks to improvements in technology allowing for quicker generation of brain images, genetic screening for diseases, and early detection of diseases, the blind neurologist could prove effective in telling you how healthy the brain he/she met was.

You might like to think of the blind psychiatrist as a waiter or bar tender who could spot a problematic customer simply by their erratic food or drink orders. A good bartender might recommend fewer drinks for customers who were already quite merry, and a good waiter might suggest a little less chilli for westerners unaccustomed to spicy food. Likewise a psychiatrist might spot when your brain is in need of some medical attention - due to lack of nutrients, or erratic electrical currents passing through it, and recommend therapy. The blind psychiatrist could tell you if the brain it encountered was misbehaving and suggest a drug to fix its behaviour.

Of all the blind men sent out to study the brain, you might like to think of the psychologist as being the most touchy feely. All of the others would use their own tools and technology to poke, prod, pry, investigate and interrogate the brain. They would then generate their own language, from Latin, Greek, and their mother tongue to describe it to you. The psychologist, however, would more likely use a little tea and sympathy; he/she would speak directly to the brain and try to understand how it felt. The blind psychologist would attempt to befriend the brain and then tell you what kind of a character it had.

Individually each of these six couldn't tell you the story of the brain. But, together these six from different branches of the brain's fact-filled family tree could describe the whole brain to you. In this series of features we have used information from these different branches to build a story for you.

The story ranges from what the brain looks like, to what functions it holds, what cells it contains, how it processes the sights sounds and smells of our world, why some people are smarter than others, where our fears and dreams are made, why some folk make us smile, to what could happen if we could harness the true power of our brains. And it begins with us opening our own minds.

GREY MATTER

Dancing, dodging, breathing, blowing, shouting, throwing, thinking, growing, everything that takes place in your body is controlled by the brain. It constantly receives information from the body, processes it, and then shuttles out commands to our limbs and organs. The mysterious grey matter encased in our skulls is not just a junction box transmitting a series of electric impulses through a black hole of consciousness. It is in fact a highly structured organ and by the end of this chapter you should be as familiar with its inner workings as with the tips of your fingers.

Firstly we have to get through the skull before we cut to the brain. We often think of the skull as one piece, but in fact the bony cap housing our brain is made of separate parts. Babies are born with a soft spot on their skull, a gap known as the fontanel where the bones have yet to fuse together. As their bones join together the lines where the bones meet are fused into sutures. In the adult skull there are six main bones. At your forehead we have the frontal bone, and on the sides at the front just above your ears we have the temporal bones. At the back is the flat occipital bone. On the top back sides we have the parietal bones.

If you receive a blow to the head, the skull takes the brunt of the blow. Instead of being transmitted into the delicate tissue, the shock is dispersed into the cerebral spinal fluid surrounding the brain. The cerebral spinal fluid, CSF, is so named because it flows in the brain and spine, and it is produced in the brain by special tissue called the choroid plexus. Choroid is a word of Greek origin meaning membrane, and plexus means group of special tissue.

The CSF is a clear liquid, renewed four to five times per day. It flows around in the brain and pools in four main caverns known as ventricles, two on the sides of the brain, one in the middle and one at the bottom of the brain at the brainstem. CSF is pretty much entirely water, containing some glucose and nutrients to help feed the brain. It also acts as a drainage system to remove toxic products from the brain. If, for example, a person had an infection in their head, puncturing the spinal chord and draining out some of the fluid to test it for toxic substances would reveal what kind of infection was in that person's brain.

WELL FED

It's not just important to keep the brain well oiled; it also has to be well fed. A constant flow of blood to the brain is vital for our survival. Though the brain is small compared to the rest of the body, it has a huge appetite for energy. It accounts for only two per cent of our body weight, yet demands 20 per cent of the body's blood supply.

The brain needs to be bathed continuously in blood to obtain sugar, to burn as a fuel. Unlike other body tissues, which store fats as a fuel reserve, brains are almost exclusively reliant on sugar from a constant stream of blood to function properly.

If any of the arteries that supply the brain with blood were to become blocked due to a clot, the supply to that area would be cut off. All functions carried out by that part of the brain would be lost. All of a sudden a person could lose the ability to see, speak, walk, talk or breathe. Therefore, it's vital for the brain to have a back-up system. This back-up is in the form of the circle of Willis, a vessel at the base of the brain.

The brain receives blood from four large arteries, two at the front and two at the back. They enter the brain separately, but are linked by a circular vessel, the circle of Willis. From here they branch out to supply the brain with energy. The circle of Willis is the system that prevents the blood supply getting clogged. Essentially it acts like a cerebral roundabout to keep blood traffic flowing through our busy brains.

PARTS

Internally the brain looks a lot like a walnut shell with a stalk coming out. It's made of two parts, called the cerebral hemispheres. Both sides look the same, but the right has more creative functions and the left is more logic orientated. Interestingly, people who are right-handed actually depend on their left hemisphere for control of their movement and speech, while people who are left-handed use their right hemisphere. Many famous creative types, artists, inventors and scientists such as Leonardo De Vinci, Henry Ford, and Marie Curie were left-handed.

These two sides are connected by a large bundle of nerve fibres known as the corpus callosum, meaning big body of nerves.

The cerebrum itself consists of layers of different tissues and cells. Inside you have the cerebral cortex, the outer skin of the brain. The word cortex comes from the Latin word for the bark of a tree. When you peel an orange you immediately release huge amounts of flavour into the air. The skin of the orange contains most of the flavour of the fruit. The brain is similar in that a lot of the good things are on the outside. The cells that control higher functions, such as talking, speaking, dreaming, are located in this outer layer.

If you were to look at a slice of cerebral tissue, you would see the cortex is grey coloured and about two to six millimetres thick. Underneath the cortex is the white matter. White matter is basically the nerve fibres that connect different areas of the brain together, forming networks. Nerve fibres branch out from cell to cell, and are covered in a fatty layer to insulate their electrical signalling, like the way the copper wires attached to the plug on your TV are covered with plastic to insulate the flow of electricity. This fatty layer gives the tissue a white colour. The high concentration of brain cells in the cortex, which process information, gives it its grey colour. This is where the phrase "use your grey matter" comes from.

BRAIN MAP

Phrenology was very popular in the beginning of the 19th century. Phrenology means "science of the mind". It involved a "specialist" or phrenologist running their fingers over a person's skull feeling the bumps and shape of their head.

The lumps on people's heads were then used to predict both the person's personality and their future station in life. A bump just above your ear could indicate an honest disposition, and make you more employable. But, for some a bump at the back of the head, could mean a predisposition to criminal activity, and jail.
Science has moved on a little since then, but the idea that we can find specific areas under the skull with specific functions is not without truth. The lumps and bumps on the cerebral cortex can be divided into four different anatomical areas, and these, in turn are associated with different functions.

The frontal lobe is under the frontal bones of the skull. This area controls speech production, elaboration of thought, control of emotions and of skilled movements.
The temporal lobes are either side of your head under the temporal bones of the skull. These lobes control recognition of sounds, tones, generation of short-term memories and speaking.

The parietal lobes are under the two paritial bones, at the rear sides of the skull. They control sensations such as touch, temperature, pressure and pain.The occipital lobe is under the occipital bone in the skull at the very back of your head. The function of this lobe is to detect and interpret visual images.

Down from the cerebrum, we encounter the cerebellum, which literally means little brain. It has a ridge-like structure on the outside and a branch like structure on the inside. The cerebellum is also known as the "tree of life" or Arbor Vitae, thanks to the tree like structure of its insides. You can see the branch-like structure of a slice taken from the cerebellum and stained purple. This area controls regulation and co-ordination of movement, posture and balance.

Under the cerebrum we find the bits of the brain that are concerned with controlling the driving power of our bodies, the basic animal urges, to create, to attack to breathe and then to sleep. These animalist bits are controlled in the midbrain and brainstem.

These bits relay messages coming from the body up to the cortex, and from the cortex down to the body. The brainstem is like a tree trunk receiving information from the roots in the body, and sending commands back from the cortex.

Humans, like all other animals, eat, breathe and have hearts that beat. All of our brains have brainstems, to control these basic functions. More developed animals, with more finely tuned skills, have cerebellums, to control finer movements. Those animals that are most developed have similar brains to us, with a noticeably larger cortex than cerebellum or brainstem. But, no animals have brains which are as complicated or developed as the human brain. Why is that?

HUMANS

At birth, chimps, our closest relatives, have a brain 80 per cent of its adult size. Their baby brains take up a volume of about 350 cubic centimetres, and develop to 450 cc. The human brain is proportionally a lot smaller at birth, with a volume of about 400 cc, yet it grows to a massive volume of 1450 cc at adulthood. Chimps can walk like us much earlier but in many other areas they do not continue to develop.

The human brain, initially slow to develop, becomes larger and more powerful over time, thanks to our extended growth period outside of the womb. After birth, the human brain, no longer constrained by the size of the birth canal, explodes in size, so that by age of four it has tripled in size. At birth the human brain makes up 11 per cent of our body weight, but consumes a massive 74 per cent of the body's energy intake.

The dolphin brain has a brain that is not just larger than the human brain at birth but is certainly more folded. So why is it that adult dolphins seem only capable of doing circus tricks? Dolphin babies can be a metre long and weigh 12 kilograms. At birth dolphin brains are already 50 per cent of its adult size, and within a year 80 per cent of its adult size.

Dolphins have larger and more folded brains at birth due to a longer gestation period of 12 months; spending three months longer than us in the womb. So, despite being better developed than us at birth, dolphins do not develop further, because during the extra three months in the womb, they have been learning in the dark. Without external environmental stimuli, dolphin brains don't develop internal connections between their neurons. Though their brains grow larger, they don't reach the same level of complexity as the slower developing human brain

Increased folding of the brain should mean a greater intellect. Our lungs contain thousands of bud-like alveoli to maximise the surface area exposed to air, to help us with our breathing. The digestive tract contains a much-folded small intestine to increase the area available for absorption of nutrients from food. So the cerebral cortex is also much-folded to allow for an increased surface area for us to make more connections, and further our thoughts. But, as you can see from the table overleaf, brains with biggest surface area are not necessarily the brightest.

We know brain size and brain complexity are not always linked. Males traditionally have heavier heads than females, containing more brain cells, or neurons. Men have about 22.8 billion neocortical neurons, while females have 19.3 billion. Yet, as we know, a bigger brain does not a better brain make.

PRUNING

Excess neuron pfuning is an essential feature of human development. From the embryo to the early adult at 10 years, the brain is constantly losing neuron cell bodies, and increasing the connections between the remaining ones. So while adults may be wiser than children, they actually have fewer brain cells.

During adulthood we lose an average of 85,000 neocortical neurons a day. This number would be more scary were it not for the fact that we start off with an average number of about 100 billion neurons in the brain. The neurons are the workhorses of the brain, yet losing some can make the brain more efficient. Neurons required for in the early stages of development can be discarded once they have served their purpose, and this is a natural process.

Neurons are very special cells because they do not divide and reproduce during the life of a cell; instead they constantly grow forming and reforming connections between each other, forming new memories and thoughts. In young adults there are approximately a staggering 39 billion kilometres of these fibres, and in older adults about the figure is 36 billion kilometres. This means that the individual brain contains enough myelin fibres to 'yo-yo' from the Earth to the Sun many times over. Neurons can transmit information at up to 250 miles per hour through their nerve fibres. The longest nerve fibre, or axon from a single neuron in the animal kingdom measures 15 feet and stretches from neck to toe of the giraffe.

However it's not just the amount of fibres you have that is important, it's how often they connect or synapse with each other. Like using the Internet, if you didn't have the connection to thousands of other computers, search engines, such as Google, simply could not work. So it's no use having billions of neurons if they are not interconnected. In the brain, every neuron has multiple connections.

Currently the estimated number of synapses in the cortex are somewhere between 60 and 240 trillion. And in the midst of all of these synapses, somewhere we have the ability to touch, see, smell taste and hear a relentless supply of information from our natural world. The next issue of Science Spin will explain this sensational side of our brain, and how it makes sense of our senses.

[In our next issue -- making sense of the scent of attraction]