Download Thinking, Learning and Intelligence: The Brain Imagine a 500 pound

Thinking, Learning and Intelligence: The Brain
Imagine a 500 pound gorilla and a 150 pound human standing side by side. The gorilla’s
brain weighs about one pound. The human brain is about three pounds. Which of the two has
the higher brain-to-body ratio? The human does! It is that difference that helps human kind to
make up for what is lacking in areas of strength, speed, endurance, vision and hearing when
compared to others in the animal kingdom.
How many of you play musical instruments? Can you read music from a sheet as you
play? It takes both sides of the brain’s hemispheres in order to do this. Sometimes while the
brain is reading, the messages to our fingers (muscles that play) get mixed and we hit a wrong
note. Try the old “pat your head and rub your tummy” at the same time routine. This activity
shows that it is rare when the brain cannot adapt quickly to dual tasks.
In this lesson we will see how our body and brain controls and influences our behavior.
If you are thinking that this is awfully close to what you study in Biology – you’re absolutely
correct! But we cannot study the mind without understanding its context – the body.
The Brain
Psychologists study the brain because it is the part of the body which controls every thought,
action and feeling. The brain is the most demanding organ of the body – it takes 20% of all our
oxygen, eats up most of the sugar we take in and operates on 20 watts of electrical power.
The Hemispheres
The brain is divided into two halves – each half is called a hemisphere. “Hemi” means
half so we have two halves of a sphere. These are referred to as the left and right hemispheres.
Each one controls the opposite side of the body – that is, the left hemisphere controls movements
and sensations on the right side of the body and the right half controls the left side.
If you were to pull these two halves apart, about midway down, you would see a bundle
of fibers called the corpus callosum. This contains several million nerve fibers that help each
half of the brain communicate with the other, transmitting all kinds of information.
The Lobes
The brain is divided into four major sections, called lobes - frontal, temporal, parietal, and
occipital. The figure below shows the lobes from the side view. If you think of this structure as
resembling a boxing glove, you won’t get confused about where the front and back parts are. (It
even has a thumb!)
Location on
Lobe
Task
Cerebrum
Frontal
At the front
Voluntary muscle movements, basic intelligence,
personality
Temporal
The sides
Major center for hearing and interpreting auditory
information. Speech center and interpretation of
Occipital
Low at the back
language (Most people have their speech center on the
left side but 25% of left-handed people have it on the
right side.)
Interprets visual information received from eyes
Parietal
The top and back
Skin sensory information and body position
Also shown in the diagram above, is the motor strip and the sensory strip. The motor strip
is located in the frontal lobe and every part of the body that is capable of movement is
represented on this section of the brain. During surgery, if the brain is exposed, the surgeon can
stimulate different parts of this motor strip with an electrically active wire, and depending on the
area touched, the arm, the leg, or the finger will move, the nose will twitch, etc. The shaded
section located in the parietal lobe is the sensory strip. If this is stimulated in an exposed brain,
the person feels a sensation in different areas – in the leg, ear, mouth etc. depending on the
specific area that the electricity hits.
The Frontal Association Area
Once the words you receive while reading this information are processed by the visual
area, this information is sent all the way to the frontal lobe. As you can see in the figure below,
this part is called the frontal association area. This area is very heavily packed with nerve cells
because its task is very complex: to interpret what is going on and telling us what to do and what
to feel. It is the core of your personality, since so many decisions are made there.
In the 1840s, a railroad worker named Phineas P. Gage was injured in a freakish accident,
which gave us clues into the nature of the frontal association area. He was pushing some
dynamite into a hole with a four-foot-long iron bar in the shape of a toothpick. The dynamite
went off, firing the bar upward through his jaw, through the front association area and on out.
Remarkably, he survived because none of the vital parts that control breathing, movement or
physical control had been damaged. Still, the injury to his frontal association area resulted in
some major changes. While he had been friendly and normal, suddenly he became someone who
swore all the time, undressed wherever he felt like it, went to the bathroom anywhere in public,
and had temper tantrums. Thus, this complex area of the brain must play a large part in what we
call social control as well as in our basic personalities. The size of this frontal association likely
reflects intelligence level from one species to another. About 7% of the brain in a dog is devoted
to the frontal lobe, 15% in chimpanzees and 30% in humans.
Hemispheres and Handedness
Ten percent of the population is left-handed. Earlier I mentioned that the left hemisphere
controls the right side of the body and vice versa. But this only refers to major body movement.
When dealing with small, fine movements, such as writing, or putting your finger in your ear,
one hemisphere has dominance. In other words, one hemisphere is always the preferred one to
use. Most people are left-hemisphere dominant and right-handed. But if the right hemisphere is
dominant, then the person will be left-handed for all fine movements.
Left-handedness does not seem to be inherited – at least not in the same sense as something
like eye color, which follows a clear family pattern. The genetic instructions that make the brain
have got to be complex beyond imagination. The parts of the “program” that develops the brain
gets slightly different signals for the left-hander and shifts the dominance to the other
hemisphere. Or if the shift isn’t complete, a very few become what is called “ambidextrous”
(left and right-handed).
The intelligence of right vs. left-handed people is about the same. But statistically the lefthander will probably do better in the arts and mathematics. And the odds increase that the
speech areas will be in the right rather than the left-hemisphere so many actors and politicians
are often lefties.
Tasks of the Hemispheres
It seems that the left hemisphere (for right-handers and most left-handers) handles verbal
or speech material. The right hemisphere deals with objects in space, art, music, some
mathematical reasoning, as well as emotional material.
A lot has been written about right-brain versus left-brain thinking and learning. Many
people assume that the differences between the hemispheres are great and that each operates in a
very specialized way. That is not really true. The hemispheres work together in virtually
everything we do through the connection of nerve fibers called the corpus callosum.
The Cerebral Cortex and the Lower Brain
All the parts discussed so far (the hemispheres, lobes, and frontal association area) are part
of the cerebral cortex. This is the outermost layer of the brain. It controls very high-levels
thoughts and takes up over two-thirds of the brain’s nerve cells. There are roughly100 billion
nerve cells. The cortex is highly infolded which increases surface area and therefore memory. If
the cortex were untwisted and spread out, it would be about the size of a large bath towel. The
nerve cells can also connect with one another in so many ways that if you emptied dump trucks
full of computers night and day until you’d filled up a football stadium, this pile would not even
come close to equaling our brain power. In fact, some people have estimated that the number of
possible different connections the brain can make is greater than the number of particles in the
universe. Think about that when you’re studying for your next test!
Below the cerebral cortex is the thalamus which is a major relay junction and sensory
coordinator of signals being sent to and from various parts of the brain.
The cerebellum is the second largest part of the brain and is part of the hindbrain section.
It controls your skeletal muscles, your body’s movement and balance. It also regulates large and
small motor movements.
“Hypo” is Latin for below and therefore, below the thalamus is the hypothalamus which is
a major control centre for homeostatic mechanisms of the body, and a major controlling gland
for the release of various hormones from other glands, including the pituitary gland.
The reticular activating system sits right at the base of the brain inside the spinal cord so
that all nerve impulses from the brain to the body and from the body to the brain must pass
through it. Thereby it takes a reading of the level of activity throughout the system as a whole.
The RAS regulates how alert or how sleepy we are. If a lot of things are going on, many
impulses arrive from the body and brain and alertness increases. If everything is quiet, this
system heads us toward sleep. It is quite sensitive to steady sounds, so a lecturer who talks
slowly and dully will put you to sleep. A change in the rhythm in the surroundings though, such
as an emergency or deeply emotional thoughts stirs up the reticular activating system.
Brain Communication
But no matter how fantastic it is the cortex will not keep the body running. For that, we
need a “lower” brain. Deep inside the skull lays the lower brain, with the cerebral cortex fitting
over and around it.
All the various parts of the brain need to communicate with each other, but how do they
do that? One way might be to string nerve cells directly from one to another in a long chain.
Why won’t this work? If you connect all the parts together and turn on a “switch”, everything
will go on at the same time, which would be a hopeless mess.
Another problem is that the brain has to be able to join different ideas. But even using
separate nerves for each though still won’t work. For instance, the brain stores the idea of red. If
we connect a nerve from red to the idea of rose, that connection would work, but how could we
get the idea of red to the idea of car without triggering rose at the same time? Or how do we get
the hypothalamus to send out a signal for rage without also sending out a signal for thirst, which
would cause us to drink instead of yell? To solve these problems, we need many nerve cells that
are separate but still able to alternate signals from one circuit to another. Fortunately we have
enough of them to do this.
The Neuron
Neurons are the basic unit of the nervous system through which signals pass. They can be
very small and microscopic, or large enough to see with the naked eye, cover short distances, or
span the distance of a metre or more, but all have the same basic structure comprised of four
parts: the cell body, the dendrites, the axon, and the axon terminal.
The cell body is the main part of the neuron which contains the nucleus. Extending
outward from the cell body are multiple fibers called dendrites. They increase the surface area
of the central cell body. It is the cell body and the dendrites that receive electrical signals from
other neurons that are attached to it. In this way, signals are passed from one neuron to another.
The Synapse
If you look at the figure below you’ll see that there is a space between the endings of the
axon and the waiting dendrites of another neuron. This space is called the synapse, which means
“junction point”. Since the neurons work by electricity, we now have another problem:
electricity will not go over a space, so it stops. And we have yet another problem: all electricity
is the same. If you cut your finger and an electrical impulse goes up to the brain, how is the
brain supposed to know if it is a “pain message” and not a message to kick out your foot?
Neurotransmitters
The solution to these problems lies in an amazing system of communication. Where the
axon ends, just before the synapse, the area is filled with small containers that look like bubbles.
They are called vesicles. Inside each of them sit thousands of chemical “messengers”. Since
chemical molecules can be any size or shape, they are not like electricity – you can identify
them. So, if a circuit is for pain, the molecules inside that container will have a unique shape that
means only “pain message” to the brain. If the circuit is for moving your arm, the container
holds different shaped molecules that will be used to signal only the movement circuit. These
molecules are called neurotransmitters.
The most common and well-studied neurotransmitter is called acetylcholine. One of its
uses is to send information from one nerve cell to another whenever we get ready to move some
part of the body. Certain kinds of food poisoning, such as botulism, shut off the release of
acetylcholine resulting in paralysis.
Another neurotransmitter that is involved in motor functions is called dopamine. A
deficiency of dopamine seems to play a role in Parkinson’s disease, which affects the body’s
ability to control movement. The same thing in part is true for Alzheimer’s disease, an illness
involving increasing loss of neural function.
Neurotransmitters exist that relieve pain and increase our sense of well-being. They are called
endorphins.
Neurotransmitters like acetylcholine are called excitatory because they cause a reaction.
There are also inhibitory neurotransmitters which shut down functions.
The Spinal Cord
The spinal cord is a slender and fragile cylinder about the size of your little finger
extending from the base of the brain to the end of the vertebral column. It is encased in vertebral
joints and is bathed the entire length with a special fluid called cerebrospinal fluid.
All nerve impulses to the body from the brain and from the brain to the body must enter
and leave the spinal cord. Sometimes, for our survival, the spinal cord must activate the muscles
long before we are even aware of it, a behavior called a reflex. In the first stages of an
emergency, the brain does not act but the spinal cord does. This happens if you touch a hot pan
on the stove. You’ve pulled your hand away even before your brain interprets the pain message.
The spinal neurons are short, direct and have very few synapses to slow them down.
The Glandular System
Communication by nerves is one system the body uses, but it also uses hormonal
messages which are passed through the body via the bloodstream. These chemicals are made
and held inside glands. All the glands and their chemical messages together make up what is
called the endocrine system.
The Pituitary Gland
The pituitary gland is called the master gland of the body. The pituitary has two jobs:
to send out messages that will start other glands working, and secondly, to determine how tall or
short we will be. The pituitary gland makes a growth hormone and that causes growth spurts
when it is produced.
Like all body systems, pituitary requires a normal environment to function properly. In
one very sad case, a mother locked her growing child in a closet and allowed him out only to eat.
As a result of the darkness and his poor treatment, he stopped growing. When freed by welfare
workers, he began to grow again. Then, as a result of error, he was sent back home. Locked in
the closet once more, he stopped growing again. Fortunately, he was finally freed a second time
and started growing again.
The Thyroid Gland
The thyroid gland and the parts connected to it look like a bow tie sitting inside the
neck. The pituitary signals the thyroid whose job is to control metabolism. Metabolism is the
speed with which the body operates. People with a very active thyroid can be jumping around all
over the place, not able to sit still. People with a slow thyroid, on the other hand, tend to be
sluggish.
The Adrenal Glands
The adrenal glands are located on both right and left sides of the body, over top of each
kidney. When they operate at full force, they create an overexcited body. This will happen in
times of emergency or crisis. At these times, the cortex signals an emergency to the
hypothalamus, which tells the pituitary, which sends hormones to the adrenal glands. The
adrenal glands then dump adrenaline into the bloodstream. Adrenaline prepares us for an
emergency: we being to breathe rapidly, blood pressure goes up, muscles tense, sugar is dumped
into the body for energy, and we are so excited that our armpits and feet sweat. This system
even sends out a chemical that will help the blood clot faster just in case we get cut! These
reactions are not designed by nature to deal with the stress of our modern world, but the body
can’t tell the difference between a real emergency and one we just think is stressful. Prolonged
stress is therefore quite harmful to the well being of the body.
Check for Understanding
Fill in the Blank
1. The cerebral cortex is divided into two halves called ___?
2. The ___ connects the two halves of the cerebral cortex.
3. The ___ runs along a fissure and is located in the parietal lobe.
4. The ___ runs along a fissure and is located in the frontal lobe.
5. Most of your movements are controlled by the ___?
6. The touch of a feather on your skin is registered by the ___?
7. Visual information is organized and interpreted in the ___?
8. Hearing and some speech functions are located in the ___?
Matching
9. Controls balance
10. Controls hunger and thirst
11. Sends messages to various parts of the brain
12. “Catches” nerve impulses in order to registered
activity level.
13. Receive electrical messages from other nerve cells
14. The spaces between nerve cells
15. Carry electrical messages to the end of the nerve cell
16. Chemicals that send messages from neuron to neuron
17. Nerve cells
18. Containers for chemical messengers
a.
b.
c.
d.
thalamus
RAS
cerebellum
hypothalamus
a.
b.
c.
d.
e.
f.
synapses
axons
neurons
dendrites
neurotransmitters
vesicles
Answer T for thyroid gland, A for adrenal gland, and P for pituitary gland.
19. Regulates metabolism
20. Activated especially during emergencies
21. May cause general sluggishness
22. The master gland
23. Helps regulate blood pressure
24. Helps determine height