by Ellen Poliakoff and Sally Bee

Illustrations by Serena Korda

BRAIN
storming

The 1990’s was hailed as the decade of the brain. We ask, what
do we really know about the elusive workings of the grey matterthat we call the brain? Neuroscientists study the nervous systemand the brain and how it can give rise to our thoughts andbehaviour. They examine how the brain works and develops andwhat goes wrong in neurological diseases such as Parkinson’s
disease and Alzheimer’s disease.
Copyright, Poliakoff and Bee, 2000

BRAIN CELLS
There are approximately 100 billion star shaped neurons in the brain and trillions ofglial cells which are like glue and support the neurons. Signals arrive at the dendrites
and then travel as electrical impulses along the cell. The long tail or axon is insulated
by a fatty myelin sheath - impulses can travel along them as fast as 120 metres per
second - that’s as much as the length of a football pitch in one second! At the end of
the axon, the electrical message is converted into a chemical message - chemical
neurotransmitters are released in tiny packages into the gap (or synapse) between theend of one neuron and the start of the next. The neurotransmitters cross the synapse
and fit into special receptors on the next cell and the signal is passed on. A “typical”
neuron has between 1,000 and 10,000 synapses or connections - with 100 billion ofthem imagine the complexity!

Adolescents may behave theway they do because theirbrains are not yet mature.

GROWING BRAINS
Although the basics of our brain circuitry are specified by our genes, our brainorganisation is highly affected by our environment. Even identical twins, with exactly
the same genes, have different brains by the time they are born because of theirdifferent experiences within the womb. During the first year of life, half of a baby’s
neurons die as their brain pathways and circuits take shape. Throughout childhood,unnecessary neurons continue to be pruned and the connections between theremaining neurons are fine-tuned. The brains of young children are highly adaptablecompared to adults. If half of a child’s brain is removed, the remaining half may takeover the functions that would have been performed by the other half - this is called
cortical plasticity. If an adult underwent the same operation, they would be severely
disabled. Similarly, it is much easier for a young child to learn to speak a newlanguage than for a middle aged person.

USE IT OR LOSE IT
The importance of a child’s environment on their emerging brain organisation has led tomany over-zealous parents frantically taking their children to zoos and museums to
make sure that they are stimulated enough. Most of this stems from work with rats,
which has shown that rats with “enriched” environments have more synapticconnections between their neurons. But this ‘use it or lose it’ mentality may be an
exaggeration - a normal level of entertainment is probably quite enough to stimulate ayoung child’s brain. Although adults brains are less flexible, experience can still change
neuronal connections. It has also been shown that mental stimulation increases andstress decreases the survival and growth of brain cells. Physical exercise also appears
to help. So, should we all be doing brain exercises to form the right neuronalconnections and to help our brain cells survive? Before you start doing your daily halfhour routine of algebra, normal levels of stimulation may be enough, but it’s still a good
excuse to turn off the TV once in a while and use your brain actively!

We might have evolved bigbrains so we could lie toother people.

WHY BIG BRAINS?
Three million years ago our ancestors had brains a third of the size of our own. The
human brain is now 4.6 times larger than would be expected in an ape of our size. So
why did we evolve such big brains? Bigger brains gave us more computational power
and we may have evolved them to invent tools and language. We might also have
evolved them to outdo other humans - skills such as lying and recognising others wholie would have been highly useful for survival in hunter-gatherer tribes. Anotherquestion is how did we evolve such big brains? Brain cells use up ten times moreenergy than the average cell, so how could we afford the energy for such big brains?
One suggestion is that the human gut size decreased in size to allow us to evolve ourbig brains.

LEFT BRAIN RIGHT BRAIN
The cerebral hemispheres are divided in half into a right hemisphere and a lefthemisphere. Sensory information goes to the opposite hemisphere, so the right hand
sends information to the left hemisphere and the left hand to the right hemisphere.
Some brain functions are performed almost entirely by one hemisphere and this iscalled lateralization. The left hemisphere is said to specialise in detailed analysis andlogic and language and the right hemisphere in holistic processing and nonverbal skills
such as face recognition and the appreciation of music. In America, you can buy selfhelp books ‘to put yourself in touch with your more emotional and intuitive righthemisphere’. But this is an oversimplification. Although some functions are lateralized,
the two hemispheres are in constant communication via a thick band of 200-250 million
nerve cells called the corpus callosum. The two hemispheres work as a team rather
than in isolation. Also, lateralization is not the same in everyone. In 95% of righthanded people and 60% of left-handed people the left hemisphere is dominant forlanguage, but some people use both hemispheres for language or are right hemisphere
dominant.

Is there a difference
between male andfemale brains?

GIRL BRAIN BOY BRAIN
Male brains are, on average, approximately 10 percent larger than female brains. But,
don’t worry girls, your brains contain more cells in certain areas and brain size is areflection of body size as well as intelligence (an elephant’s brain weighs 6 Kg). There
has been much research into differences between male and female performance ondifferent tasks and how this may relate to brain organisation. Women performmarginally better on tests with words (could explain why men are worse atcommunicating!) and men are slightly better at spatial skills (could explain why women
can’t map read!). But researchers have found few meaningful differences between themale and female brain - there are much larger differences between individuals
regardless of gender.

BRAIN BOXES
So what do all the different parts of the brain do? People have always tried to pin down
different functions to different areas of the brain. Much has been found out using
patients who have brain damage to a small area of brain. By seeing what it is that thepatients cannot do, we can try to predict what this area is doing in a healthy brain.
Damage to just a small area can have profound effects on a person (this disproves thepopular myth that we only use 10% of our brains!) For example, a patient with damage
to the amygdala (a specific part of the cortex) ceases to perceive emotions properly inthemself and in others and one such patient could not understand why other people
found soap operas of any interest! So, we can deduce that the amygdala is importantfor emotion. But this approach is tricky because many different brain areas can beinvolved in specific tasks.

Drugs working in
the brain.

DRUGS IN THE BRAIN
Many drugs work because they are similar chemicals to neurotransmitters and so areable to fit into their receptors (see Brain cells) or prevent the breakdown ofneurotransmitters. In 1973, neuroscientists discovered that the brain has receptors foropiods (such as morphine and heroin) and these are located in the areas of the brain
important for breathing, pain and emotions. Nobody knew why we have these receptors
in the brain until endorphins were discovered. These are the brains own opiods and arereleased in times of pain or stress. Commonly used drugs such as caffeine and alcohol
also affect the brain. Alcohol acts on the same receptors as some anaesthetics andcaffeine acts on multiple sites in the brain. Knowing about how neurotransmitters workin the brain and where the different types of receptor are located helps in the design ofdrugs to treat specific diseases such as Parkinson’s disease.