New Scientist Brain

8/14/2019 New Scientist Brain

http://slidepdf.com/reader/full/new-scientist-brain 1/14

Instant Expert: The Human Brain

• 11:58 04 September 2006

• NewScientist.com news service

• Helen Philips

The Human Brain - With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our

cutting edge special report .

The brain is the most complex organ in the human body. It produces our every thought, action, memory, feeling

and experience of the world. This jelly-like mass of tissue, weighing in at around 1.4 kilograms, contains a

staggering one hundred billion nerve cells, or neurons.

The complexity of the connectivity between these cells is mind-boggling. Each neuron can make contact withthousands or even tens of thousands of others, via tiny structures called synapses. Our brains form a million new

connections for every second of our lives. The pattern and strength of the connections is constantly changing

and no two brains are alike.

It is in these changing connections that memories are stored, habits learned and personalities shaped, byreinforcing certain patterns of brain activity, and losing others.

Grey matter

While people often speak of their "grey matter", the brain also contains white matter. The grey matter is the cell

bodies of the neurons, while the white matter is the branching network of thread-like tendrils - called dendritesand axons - that spread out from the cell bodies to connect to other neurons.

But the brain also has another, even more numerous type of cell, called glial cells. These outnumber neurons ten

times over. Once thought to be support cells, they are now known to amplify neural signals and to be as

important as neurons in mental calculations. There are many different types of neuron, only one of which isunique to humans and the other great apes, the so called spindle cells.

Brain structure is shaped partly by genes, but largely by experience. Only relatively recently it was discovered

that new brain cells are being born throughout our lives - a process called neurogenesis. The brain has bursts of growth and then periods of consolidation, when excess connections are pruned. The most notable bursts are inthe first two or three years of life, during puberty, and also a final burst in young adulthood.

How a brain ages also depends on genes and lifestyle too. Exercising the brain and giving it the right diet can be

just as important as it is for the rest of the body.

Chemical messengers



The neurons in our brains communicate in a variety of ways. Signals pass between them by the release and

capture of neurotransmitter and neuromodulator chemicals, such as glutamate, dopamine, acetylcholine,noradrenalin, serotonin and endorphins.

Some neurochemicals work in the synapse, passing specific messages from release sites to collection sites,

called receptors. Others also spread their influence more widely, like a radio signal, making whole brain regions

more or less sensitive.

These neurochemicals are so important that deficiencies in them are linked to certain diseases. For example, aloss of dopamine in the basal ganglia, which control movements, leads to Parkinson’s disease. It can also

increase susceptibility to addiction because it mediates our sensations of reward and pleasure.

Similarly, a deficiency in serotonin, used by regions involved in emotion, can be linked to depression or mooddisorders, and the loss of acetylcholine in the cerebral cortex is characteristic of Alzheimer’s disease.

Brain scanning

Within individual neurons, signals are formed by electrochemical pulses. Collectively, this electrical activity

can be detected outside the scalp by an electroencephalogram (EEG).

These signals have wave-like patterns, which scientists classify from alpha (common while we are relaxing or

sleeping), through to gamma (active thought). When this activity goes awry, it is called a seizure. Some

researchers think that synchronising the activity in different brain regions is important in perception.

Other ways of imaging brain activity are indirect. Functional magnetic resonance imaging (fMRI) or positronemission tomography (PET) monitor blood flow. MRI scans, computed tomography (CT) scans and diffusion

tensor images (DTI) use the magnetic signatures of different tissues, X-ray absorption, or the movement of

water molecules in those tissues, to image the brain.

These scanning techniques have revealed which parts of the brain are associated with which functions.

Examples include activity related to sensations, movement, libido, choices, regrets, motivations and evenracism. However, some experts argue that we put too much trust in these results and that they raise privacy

issues.

Before scanning techniques were common, researchers relied on patients with brain damage caused by strokes,head injuries or illnesses, to determine which brain areas are required for certain functions. This approach

exposed the regions connected to emotions, dreams, memory, language and perception and to even more

enigmatic events, such as religious or "paranormal" experiences.

One famous example was the case of Phineas Gage, a 19th century railroad worker who lost part of the front of his brain when a 1-metre-long iron pole was blasted through his head during an explosion. He recovered

physically, but was left with permanent changes to his personality, showing for the first time that specific brainregions are linked to different processes.

Structure in mind

The most obvious anatomical feature of our brains is the undulating surfac of the cerebrum - the deep clefts are

known as sulci and its folds are gyri. The cerebrum is the largest part of our brain and is largely made up of the

two cerebral hemispheres. It is the most evolutionarily recent brain structure, dealing with more complex

cognitive brain activities.



It is often said that the right hemisphere is more creative and emotional and the left deals with logic, but the

reality is more complex. Nonetheless, the sides do have some specialisations, with the left dealing with speechand language, the right with spatial and body awareness.

See our Interactive Graphic for more on brain structure

Further anatomical divisions of the cerebral hemispheres are the occipital lobe at the back, devoted to vision,

and the parietal lobe above that, dealing with movement, position, orientation and calculation.

Behind the ears and temples lie the temporal lobes, dealing with sound and speech comprehension and someaspects of memory. And to the fore are the frontal and prefrontal lobes, often considered the most highly

developed and most "human" of regions, dealing with the most complex thought, decision making, planning,

conceptualising, attention control and working memory. They also deal with complex social emotions such asregret, morality and empathy.

Another way to classify the regions is as sensory cortex and motor cortex, controlling incoming information,

and outgoing behaviour respectively.

Below the cerebral hemispheres, but still referred to as part of the forebrain, is the cingulate cortex, which deals

with directing behaviour and pain. And beneath this lies the corpus callosum, which connects the two sides of the brain. Other important areas of the forebrain are the basal ganglia, responsible for movement, motivation

and reward.

Urges and appetites

Beneath the forebrain lie more primitive brain regions. The limbic system, common to all mammals, deals with

urges and appetites. Emotions are most closely linked with structures called the amygdala, caudate nucleus and

putamen. Also in the limbic brain are the hippocampus - vital for forming new memories; the thalamus - a kindof sensory relay station; and the hypothalamus, which regulates bodily functions via hormone release from the

pituitary gland.

The back of the brain has a highly convoluted and folded swelling called the cerebellum, which stores patterns

of movement, habits and repeated tasks - things we can do without thinking about them.

The most primitive parts, the midbrain and brain stem, control the bodily functions we have no consciouscontrol of, such as breathing, heart rate, blood pressure, sleep patterns, and so on. They also control signals that

pass between the brain and the rest of the body, through the spinal cord.

Though we have discovered an enormous amount about the brain, huge and crucial mysteries remain. One of

the most important is how does the brain produces our conscious experiences?

The vast majority of the brain’s activity is subconscious. But our conscious thoughts, sensations and perceptions- what define us as humans - cannot yet be explained in terms of brain activity.



The Human Brain















Brain FAQ

1. What is the brain?

The brain is simply a collection of neurons (nerve cells) and other cells, gathered together in one place to

simplify the wiring. A brain can be just a handful of cells, as found in some simple invertebrates, or billions, asin humans.

2. What does it do?

It allows animals to adapt their behaviour to changes in the environment, on a much quicker timescale than

evolution. It helps them collect information, act on that information and store the result for future reference - inother words, it is a sensory system, a motor system and a memory.

3. What is special about the human brain, compared to the brains of other primates?

Human brains, particularly the cerebral hemispheres are bigger and better developed than in other primates. Thefrontal and prefrontal lobes of the cerebral hemispheres deal with complex kinds of thought and socialinteraction, such as planning, decision making, empathising, lying, and making moral judgements. But

corrected for body size, the differences are surprisingly small.

The difference between a human brain and a chimp or gorilla brain seems to be largely the way neurons are

connected. Humans have several unique genes that seem to control nerve cell migration as the brain develops,and different patterns of gene expression in the brain. So, the machinery doesn’t look that different, but it

certainly works differently.

As for non-primates - other mammals have smaller brains, with less well developed frontal lobes. Further down

the evolutionary tree, animals lose the cortex altogether, with reptiles having a brain that resembles just our own brainstem. In simple animals, the brain becomes more of a swelling at the top of the nerve cord or around the

mouth area.

4. How does the human brain think and solve problems?

All brain activity takes place as electrochemical signals. The signals form within neurons, pass along the branch-like axons and - by the release neurotransmitter chemicals - they jump from one neuron to the next

across gaps called synapses.

The pattern, size, shape and number of these signals, what they communicate with, and the region of the brain

in which they happen, determine what they achieve. It’s a bit like the wiring and components of a computer andthe sequence of coded 1s and 0s it uses, only far more powerful.

Most people define thought as an active and conscious brain activity - in other words, a brain signal we are

aware of. No one knows why some brain signals, such as those controlling our muscles or heart beat are

completely subconscious.

Solving problems can happen in two ways. It can be a type of thought or calculation - pulling information frommemory, filtering new information, combining it all and weighing up alternatives. Or it can be a gut instinct – a

decision made by the more primitive emotional part of our brain, like the mental equivalent of a reflex.



The most creative problem solving can be a long term process of both mulling things over in thought and in our

unconscious mind, with the answer finally popping out.

5. How are memories stored in the human brain?

There are several types of memory - for facts, skills or events - and several brain areas devoted to it.

At a neuronal level, memory is any change that increases the chance of a signal passing along a particular

pathway, or that increases the size or strength of this signal. At first the change can be a simple increase in theamount of signalling chemical released. Gradually, the connections are built up physically with more and biggersynapses. Eventually more branches may form.

For these more permanent changes, genes become active and produce building materials to form the structural

changes. But memories are never stored in an immutable form - they are continually being changed and

reactivated.

6. Is language hardwired into the brain?

Some people argue yes, others no. Linguist Noam Chomsky famously argued that it was hardwired - that all

babies are born with the nuts and bolts of language and grammar rules.

Other researchers say that language and its rules are all picked up through experience – a process called

statistical learning. They believe that the brain is born naïve, and learns through example.

Yet others believe the truth lies somewhere in between. Under this scenario, we are all born with a hardwired

ability to pick up language and to extract rules from examples, but that the words, concepts, syntax and

grammar are all learned.

7. What do alcohol and drugs do to our brains?

They enter the brain and interfere with the normal signalling mechanisms. Often drugs of abuse are very similarto one of the natural neurotransmitter chemicals. Marijuana contains compounds similar to our natural

cannabinoids, morphine and heroin mimic our natural pain-killing opiods, amphetamines and cocaine tinker

with dopamine and serotonin signalling.

They can either mimic, block or extend the usual signals, hence the wide variety of sensations and behaviours

they lead to. All drugs of abuse have some effect on our dopamine and opioid systems, which provide some of

our sense of pleasure and reward. This means the reward system can be corrupted into addiction by drug use

over extended periods, or in people with certain genetic predispositions.

8. Is it true that we only use a small amount of our total brain capacity?

At any one time, yes. Some people say 10%, others say 1%. But every part of the brain has a function, so we get

round to using it all at some time.

And it’s not as though using more of our brain at one time would necessarily make us smarter. In fact it would

be disastrous – something like a massive epileptic fit.

Certainly there’s no simple relationship between how much brain activity there is and how intelligent we are.

When people are being creative, their brain waves are actually quieter than less creative types, and the better

you are at something, the less brain activity there needs to be.



9. What are dreams?

Dreams are a type of brain activity occurring during or near sleep. The most vivid seem to happen during asleep stage called REM (rapid eye movement). Emotional, visual and other sensory areas are very active during

dreams, and many researchers think that they might be a kind of “offline” filing, sorting and consolidation time

for the brain.

10. Could you build an artificial human brain?

No – at least not yet. There has been some success at mixing electronics with real cells. Some experiments havegot real-looking signals to come in and go out of artificial brains, and even to result in learning.

Devices similar to pacemakers can substitute for simple functions or control epilepsy, and prosthetic sensory

systems can give some sensation back. But the fundamental complexity of the human brain is so great that no

electronic system could currently come close.

11. What is consciousness?

This is the biggest mystery in the study of the human brain. Consciousness is the opposite of the subconscious.

It is a state of wakefulness and awareness, but also more, in that it also includes our sense of self, a feeling of embodiment and of having a sense of a personal history - a "stream of consciousness".

Wondering why people have a clear sense of themselves has long been the realm of philosophers,. But morerecently, brain researchers have sought to identify regions of the brain that correspond to consciousness.

However, even if they can identify the regions, or types of brain activity, that differ between conscious and

subconscious states, the problem of why pulses of chemical and electrical signals can feel like anything at all,remains.



WEBLINKS

• The Human Brain, Franklin Institute, US

• Brain tutorial, Standford University, US

• Comparative mammalian brain collection, BrainMuseum.org

• Internal structure of the human brain, interactive study module, University of Alberta, Canada

• Dissections of the real brain, Virtual Hospital• Navigable atlas of the human brain, Michigan State University, US

• Whole brain atlas, Harvard Medical School, US

• How your brain works, HowStuffWorks.com

BOOKWORM

• The Wisdom Paradox by Elkhonon Goldberg

• The 21st -Century Brain: Explaining, mending and manipulating the mind by Steven Rose • Dreaming Reality: How dreaming keeps us sane, or can drive us mad by Joe Griffin and Ivan

Tyrrell

• New Scientist's selection on consciousness

• The Physiology of Truth: Neuroscience and human knowledge by Jean-Pierre Changeux

• The Space Between Our Ears by Michael Morgan

• Mind Time: The temporal factor in consciousness by Benjamin Libet

• The Museum of the Mind by John Mack

• This Is Your Brain on Music, by Daniel J Levitin

http://www.fi.edu/brain/index.htm

http://www.stanford.edu/group/hopes/basics/braintut/ab0.html

http://brainmuseum.org/

http://web.psych.ualberta.ca/~iwinship/studyguide/brain_study.htm

http://www.vh.org/adult/provider/anatomy/BrainAnatomy/BrainAnatomy.html

http://www.msu.edu/~brains/humanatlas/

http://www.med.harvard.edu/AANLIB/home.html

http://www.howstuffworks.com/brain.htm

http://www.newscientist.com/channel/being-human/brain/mg18725122.300

























http://www.fi.edu/brain/index.htm

http://www.stanford.edu/group/hopes/basics/braintut/ab0.html

http://brainmuseum.org/

http://web.psych.ualberta.ca/~iwinship/studyguide/brain_study.htm

http://www.vh.org/adult/provider/anatomy/BrainAnatomy/BrainAnatomy.html

http://www.msu.edu/~brains/humanatlas/

http://www.med.harvard.edu/AANLIB/home.html

http://www.howstuffworks.com/brain.htm











Documents

New Scientist Brain