Download Brain Structure

Lesson
I
Functtoft
N
KeyTe,rrns
axon
brain stern
cerebral hernispheres
co!:tex
dendrite
limbic systern
neural plasticity
neuron
neurotransmitter
sensory flooding
sensory gating
sl.napse
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What YouWill Learnto Do
* i'lelate the strtrcture and function of the trrain to the lear.ning process
LinkedCoreAbitities
e Euild your capacity for life-lorrg Iearlling
a Apply {lritical trtrinking Techniques
SleiJJs
and KnawledgeYouWiff 6ain Atongtke Way
&
Identify key areas and function of the rnidbrain/limbic $v$tem
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Associate major regions of'ttre hrain to their func{irxls
Hxplain the function cf a neurcn
Explain the three elements involved in transmitting stimulus from outside the
bodyto the brain
a
Assessthe processrequired to enhance brain power
a
Defrne the kev words containedin this lesssn
fn*rsductisn
This lesson introduces you to the most marvelous and mysterious paft of your
anatomy-the human brain. Most humans never totally discover or exert the full
potential of their brain. In this lessonyou explore current researchon what the
brain is (structure) and how it works (function). You learn practical ways to apply
complex concepts that put you in control of your own mind.
Evslu*isn0f *ke t{urnsnSrain
One way to look at the brain's structure is based on the theory of evolution, Only
100,000years ago,the ancestorsof modern man had a brain weighing only about a
pound-roughly a third of the weight of our current brain. Most of this increased
weight is becauseof a much larger cerebral cortex. Here most of the thinking that
makes human beings such unique mammals occurs.This tremendous growth is an
important aspectof the evolution of the human brain.
TheTriuneBrain
An early description of the human brain was conceived by neurologist Dr. Paul
Maclean that attempted to explain its structure in terms of how it has evolved.
According to Maclean's theory three separateand distinct brains exist, from oldest
to more recent.As each brain evolved,the older brain was retained for its specialized functions, and the new brain simply formed around it.
conceptof the human
Maclean'stheoryprovidesa simple,easy-to-understand
brain.This descriptionrelatesdirectlyto evidenceabouthow thebrain actually
works,asyou will seein the sections"BrainFunctiorf'and "Downshifting"laterin
thislesson.
Figure2.1.1:Thetriune
brain.
The human brain, as shown in Figure 2.1.1,has three parts: the neocortex (mushrooming out at the top), the limbic system (in the middle), and the brain stem (at
the base).
The neocortex, sometimes called the cerebralcortex,is believedby researchersto
have grown out of the limbic systemat some time in human evolution. Though not
exclusively,the neocortex is where most higher-order and abstract thoughts are
processed.The two hemispheres of the neocortex also handle input from our sensory systems,making connections between various stimuli, such as associating
what we seewith what we hear. This makes comprehension possible, and is how we
make it all meaningful.
The neocorte& the most newly developedpart of our brain, also attachesfeeling
and value to stimuli it receives.When humans learn, the structure and chemistry of
nerve cells in the neocortex are changed
Let's take a closer look at how the brain functions, from top to bottom, and how it
interacts with the rest of the body.
The limbic system, once thought to be associatedexclusivelywith emotion, is now
known to process not only emotional responsebut also a number of high-level
thinking functions, including memory.
The brain stem, sometimes called rhe reptilianbrain (R-complex),is considered to
be the oldest part of the brain from an evolutionary standpoint. It follows then that
much of the processing of basic survival needs (eating, breathing, and the "fight or
flight" response)occurs here. Fight or flight is the common terminology for a complex set of reactions to a perceivedthreat, really the organism'sability to go on red
alert and respond quickly. Many of the body's systemsrespond automatically to
increasethe chance of survival when under attack,
BrainFunction
The brain is vital to human understanding and the abilityto learn. Perhapsyou've
heard of "higher level" thinking skills.This phrase refers to the level of information
processing and responserequired by a particular task. Somecomplicated tasks can
require a high level of information processing.
For example,when you touch a hot stove,you pull your hand away quickly. That
activity does not take much thinking, and it had better not take a lot of time! In fact,
your nervous system is designedto processinformation like that automatically, with
little help from the neocortex.
Think about gettingburned.\Alhatinformation would be helpful to storelong term
Maybethe size,shape,and color of the heat sourcewill help
about that experience?
you to avoid the problem in the future. But the "how to" of pulling awayyour hand is
best left to the quick reactionsof nervesand muscles.Giventhe brain structurepresented in Triune Brain theory,which of the three major regionsis probably in charge
of the burn response?
If you said the brain stem,you'repretty close.In fact, musclescan react to nerve
impulses without thoseimpulsesevertravelingup the spinal cord to the brain. The
withdrawal reflex,where the finger is pulled away from the pain as muscles contract, is the simplestact that the nervoussystemcan perform. It is automatic and
unconscious;it doesnot involve any higher-levelthinking.
Downshifting
Now let'slook at a processwe call downshifting.From the top to bottom view
describeswhat occurswhen infordescribedin the previoussection,dornmshifting
mation processingmovesfrom the higher-levelthinking regionsof the brain, the
into the brain stem and eveninto the
neocortexand eventhe limbic system,do'o,m
\A/hy
reflex.
does
this
happen?
!t/hy give up the ability to
automatic responsesof
ponder and reflectand insteadrevertback to instinct and involuntary reflexes?Fear
and intimidation are two main reasonsdownshiftingoccurs.
In the presenceof perceivedthreat, survivalbecomesimportant and the brain discerns the need for speed.Like the burn examplein the previoussection,your nervous systemis fine-tuned enough to automaticallyrevert to more efficient
processingmethodsto keepthe organismsafeand sound. In other words, the brain
will doumshift from neocortexinvolvement to rely more heavily on the survival and
emotional processingof the brain stem and limbic systemwheneverthe organism
perceivesa threat.
Perhapsyou havea lot at stakein the outcome of that upcoming geometrytest.
Maybe you won't passthis year if you don't completea major r,tritingassignment'Or
maybe you know someonewho believesbeing tough helps motivate people to perform better.Sometimestough comes out more like put-downs and threats,instead
of inspiration, high standards,and a belief in your abiliry to succeed.
Psychologicalthreatscan produce the samekind of flight or fight responseneeded
when an animal is under attackfrom a predator.And to be more efficient,the brain
dovrrnshifts.
Trouble is, you needyour whole brain involved,especiallythe neocortex,to solve
theseproblems.Fight or flight reactionswon't help. Notice when your emotions
react and your mind seemsto shift into an automatic mode of response.Being selfaware of a dor,rrnshiftgivesyou the chance to incorporate your higher-level thinking
skills in evaluatingthe situation.Then your whole brain is in operation;ideasand
creativity can flow to help you determine a better way to respond to the challenge at
hand. This enhanced state of being fully engagedand aware is what we call whole
brain activation. Taking in and processing information in many different ways activatesthe vuholebrain.
Figure 2.1.2:Anotheruiew
of the brain.,ako showing
threeseparatearees.
MqiorSrainAreas
The brain is composed of a number of different regions, each with specialized functions. Figure 2.L.2 shows a view of the brain's structure and function, also with
roughly three separateparts.
The brain's central core, which includes the brain stem and the midbrain, is quite
different than the cerebral cortex that envelopsit. The central core is relatively simple, older and its activity is largely unconscious. In contrast, the cortex is highly
developed and capable of the deliberation and associationsnecessaryfor complex
thinking and problem solving. In humans, its size and function has increased
rapidly; the older poftions of the brain remain relatively static.
TheSrsinStem
The brain stem seemsto be inherited almost "as is" from the reptilian brain. It
consists of structuressuch as the medulla (controlling breathing, heart rate, and
digestion) and the cerebellum (which coordinates sensory input with muscle
movement).
TheMidbrain
The midbrain includes features that appear intimately connected to human emotion and to the formation of long-term memory via neural connections to the lobes
of the neocortex. The structures contained here also link the lower brain stem to the
thalamus-for information relay from the senses,to the brain, and back out to muscles-and to the limbic system.
The limbic system,essentiallyalike in all mammals, lies above the brain stem and
under the cortex. It consists of a number of interrelated structures. Researchershave
linked the limbic systemto hormones, drives, temperature control, and emotion.
One part is dedicated to memoryformation, thus explaining the strong link
between emotion and long-term memory.
The limbic systemincludesthe followingparts:
The hypothalamus is instrumental in regulating drives and actions. Neurons
affecting he.rrt rate and respiration are concentrated here. These direct most of
the physical changes that accompany strong emotions, such as the "flight or fight"
response.
a
The amygdala appears connected to aggressive behavior.
o
The hippocampus plays a crucial role in processing various forms of information to
form long-term memories. Damage to the hippocampus will produce global retrograde amnesia.
One important featureof the midbrain and limbic systemis the reticular activating
system (RAS).It is this areathat keepsus awakeand awareof the world. The RAS
acts as a master switch that alertsthe brain to incoming data-and to the urgencyof
the message.
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The forebrain,which appearsas a mere bump in the brain of a frog, balloonsout
into the cerebrum of higher life forms and coversthe brain stem like the head of a
mushroom. This, the newestpart of the human brain, is calledthe neocortex,or
in Figure2.1.3.
cerebralcortex,and is shor.tm
TheNeocortex
key NsteTerm
The structure of the neocortexis complicated.Most of the higher-levelfunctions
associatedwith human thought are enabledhere.
BrainHemisphere
In humans, the neocortexhas evolvedfurther than in other mammals,into the two
cerebral hemispheres.The wrinkled surfaceof the hemispheresis about two millimeters thick and has a total surfaceareathe size of a desktop (about 1.5square
meters).
SensoryCort€x
(feetins) \
Motor Corte
(moving)
Frontal Lobe
(prcblen solving)
TempoEl Lobe
(hearng)
Retjcular Fomalion
{rousal)
Parietal Lobc
(touching)
Occigiral Lobe
tseelns)
Cerebellum
(balancing)
Brain Stem
{Datru a\ to bod!)
looked at
top, the
camposed of
ntected
Iobesand
? igure.2. l. 3:'l'he neor:ortex
and all o.f its carrysorrcnts.
Remember that there is syrnmetry between hemispheres;however,not every specialized region is found on both sides.For example,highly specializedlanguage centers exist only in the left hemisphere.The brain coordinates information between
the two hemispheres,and does so with startling speed and skill.
The following is a brief description of the four lobes that make up the cerebral hemispheres,or neocortex.
Frofttal Lobes
The frontal lobes occupy the front part of the brain and are associatedwith making
decisions, planning, and voluntary muscle movement. Speech,smell, and emotions
are processedhere as well. The frontal lobes control our responsesand reactions to
input from the rest of the system.The saying "Get your brain in gear" refers to activity in the frontal lobes.
ParietalLobes
The parietal lobes are most closely associatedwith our senseof touch. They contain
a detailed map of the whole body's surface.More neurons are dedicated to some
regions of surface area than others. For example,the fingers have many more nerve
endings than the toes, and therefore they have more associatedareasin the brain
for processing.
The parietal lobe of the right hemisphere appearsto be especiallyimportant for
perceiving spatial relationships. The recognition of relationships between objects in
spaceis important to activities such as drawing, finding your way, construction, and
mechanical or civil engineering.
Temporal
Lobes
The temporal lobes are concerned with emotions, and also contain the primary
auditory cortex, which processessound. Doesnt this provoke wonder at the profound connection between music and strong emotion?
0ccipital Lobes
The occipital lobes are the primaryvisual cortex. This area at the back of the brain,
just above the cerebellum, processesstimuli from our eyes,via the optic nerve, and
associatesthat information with other sensoryinput and memories.
Recall that areascrucial to long-term memory also reside at the back of the brain.
These association areasinterpret sensory data by relating it to existing knowledge,
and are essentialto memory formation. More information on memory is included
in later sections of the text.
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SensoryCortexandMotorCortex
Regionscalledthe sensorycortex and the motor cortex are sandwichedbetweenthe
frontal and parietal lobesat the top of the head.Theseareasspecializein the control
of movement and in receivinginformation from the body'sprimary sensorysystems
(vision,smell,taste,touch, and sound).
of Time
Awareness
the lobesto the front and the back of the brain seem
Accordingto some researchers,
to be awareof the passageof time; thus the frontal lobe of the neocortex,shown in
Figune2.1.4,appearsto be responsiblefor planning, decision-making,and risk-taking while the back of the brain storesmemories.
The rmiddlesectionis focusedon experiencingthe presentmoment becauseit
housesthe primary sensoryand motor cortex.It is busily processinginformation
from our five sensesand sendingcontrol signalsback out to our muscles.
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The nervous systemlinks the body to the externalenvironment through sensory
organs,permitting us to see,hear,taste,smell,or feel and to respondto slimuli.
Through your five sensesyou know that the air is cold, it's earlymorning, and someone has a fire burning. The hot chocolatesmellswonderful and the birds are
singing.But how do you know?
SensorySystems
The live most commonlyknov,n sensorychannels-our eyes,ears,skin, nose,and
tongue-all rely on specializedreceptorcellsto take in data from the externalworld.
Then, mechanical,chemical,and electricalprocessestransform the glow of the sun
in your eyesand its heat on your skin into electricalimpulses and send them sparking along nerve fibers (calledsensoryneurons).Travelingat speedsup to 290 miles
per trour,jumping microscopicgaps (calledsynapses)along the way, thesemessagesmake their way to nerve processingcenters(calledinterneurons)in the spinal
cord and brain. They then connect back out to your musclesand glands(called
motor neurons),causingyou to sweatin responseto the sun'sheat.
Figure2.1.4:'I?rcktbesto
fhefron{ and.brlck of the
brnin rereGwareof the pe*sageof time.
F\aoding
andGsting
Ssrus,ssry
Key NoteTermq
sensorygating* alsg'
called the neuron '
spike point, regulates
the tansmission of ,
stimuli to the brain.
sensoryflooding- :
sensory overload,
this happenswhen
too much data is getting through to the
brain.
axon * long fibers
that send electrical
impulses and release
neurotransmitters.
dendrite - any of the
usually branching
protoplasmic
processesthat conduct irnpulses
towards the body of a
:
nerve cell.
neuron-agrayishor
reddish granular cell
with specialized ,
processesthat is the
fundamental functional unit of new-'
cous tissuein the
' . ,l
brain.
. . .
neurotransmitter- a
chemical molecule
'
(asnorepinephrine
or acertylcholine)that
transmits nerve :
impulses acrossa :
s),napse,within and..
between brain cells.
A largeamount of data comesinto the brain all the time. \{recan'tand don't pay
attention to all of it. A "go or no go" signaloccursto regulatethe transmission of
stimuli. This is calledthe neuron spikepoint, or sensorygating.Without this monitoring,sensoryoverload,or flooding,would occur.This automaticphysicalprocess
is a key aspectof what we actuallyprocesson a consciouslevel.
Sensoryflooding is what happenswhen too much data is gettingthrough. There is
some indication that disorderssuch as autism are,in part, causedby this tlpe of
physiologicaldatatransmissionproblem.
NeuronStructure
The arm and hand in Figure2.I.5 areusedto illustratea neuron.The arm representsthe axon, long fibers that sendelectricalimpulsesand releaseneurotransrnitters. The hand is like the cell body and the fingersare like dendrites.
muscles,or other
Messages
aretransmittedaselectricalimpulsesfrom the senses,
message
to other
neurons.The neuron processes
the impulseand then sendsthe
neuronsvia axons.\.Ar'hen
the impulsereachesthe end of the axon,the dendrites
pick up the signalas a chemicalneurotransmittersynapse.
Neurotransrnitters
Neurotransmitters
are chemicalin natureand areusedto acceptan electrical
impulse from the axon at a s).napseand relayrt to the dendrites.
and affectbehavior
The neurotransmitterscarryexcitatoryor inhibitory messages
patternssuchaspain and pieasure.
AmazingFactsAboutNeurons
. UO,o 100bitlion nerve cellsact as information specialistsin the brain and spinal
cold
r Tensof billionsof messages
impulseseveryt'ewseconds
travelaselectro-chemical
of everyday of your entiie lifetime.
o Somesinglenervecells,suchasthe sciaticnervein your leg,containdendrite
branches3 feetlongc Along theselarge nervefibers,impulsestravelup to 290miles per hour.
Figure2.J.5:An nrtn ond
lrcnd.cansLtotultaw a
neilr'ltr works.
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The human brain has evolvedover time to a three-pound massof tissue,sparking
with electro-chemical interactions. Our jaws and teeth have gror,rmsmaller,infancy
and childhood last longer,and we physicallymature and reproduceat an older age.
All these evolutionaryadaptationshave reservedboth time and energyto devoteto
brain development.
IlumanThought
With the advantagesof a largerbrain and more processingpower,humans now are
able to solveproblems,make decisions,and generateoptions.Emotions arenow
rich and complex,givingus the ability to fall in love,nurture eachother,and hope
for a better future.The wonder of a more highly developedlimbic systemand neocortex is lived out eachday in processeswe often take for granted.
Looking closelyat complexprocessessuch as learning,and understandinghow
With understandingcomesthe
theseeventsoccur can bring further advantages.
ability to make choicesto improve our lives.And these choices can literaily make
our physical body work better by increasingthe size,number, and connections
between neurons,the basic cellularbuiiding block of the human nervoussystem.
Growing0endrites,MakingConnections
The billions of nerve cellsconnectto eachother in billions of combinations,forming trillions of pathways for nerve signals to follow. This results in dendritic growth.
The dendrites continue to grow throughout your lifetime.
NeuralPlasticiV
In addition to adding and refining neural networks through the growth of dendrites,
the human brain is capable of adapting specializednerve function for another critical use when calledupon to do so.
Neural plasticity concerns the property of neural circuitry to potentially acquire
(given appropriate training) nearly any function. For example, the connections
between the eye and primaryvisual cortex suggestthat neural circuits are wired by
evolution exclusivelyfor sight.
The brain'samazingadaptiveability has been demonstratedthrough the research of
many scientists.Neuralptasticityis an important adaptation.Similar to other tissue
plasticities,it tends to occur when ca-lledupon for specialskill development, or finetuning existingcapabilities.For example,n'hen a musicianmakesspecial demands
for left hand skills in the processof learninghow to play the piano, the brain adapts
by increasingthe number of neural circuitsin the right primary motor cortex.
Similarly,the areaof the brain devotedto the right indexflngertip (what'sknor,rmas the
readingfinger)is largerin Braillereaderscomparedto that for their non-reading fingertips,or for sightedreaders,accordingto researchers
Pascual-Leone
& Torres,lgg3.
NOTE
To learn more about the researchdone by Pascual-Leoneand Torres,go to
',,hffifi{cogprints.ecs.soton.ac.uk/archiue/00002
255/ 00lbuss.htm.
InterestingFactsAboutBrainGrowth
o Weproduce no newnerve cellsafter roughly the time of birth. Thesecells must be
nurtured becausethey must work for the next B0yearsor so.
e Our infant brain demonsffates
on-the-jobtraining;the brainis beingusedat the
sametime it is beingassembled.
o Wearefairtyhelplessat birth. Lessthan I percentof the portion of our brain cir' cuitry that will be dedicatedto receivingsensoryinformationneededfor perception
and cognition is functional at that point.
-o...{lbirth, f 00 biflionr.rervecellsin our cerebralcor.texset aboutwiring incredibly
complexcircrrits(some5,000to 10,000connectionsto eachnervecell).
r Throughlearningmechanismsin the brain,the brain continuesto rewire and
changeits circuitrythroughoutour lives.
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Researchers
have identified different types of neural systemsthat store memories,
eachwith their oum focus and purpose.Perhapsyou'veheard of long- and shortterm memory.That'sone way to categorizememory systems,in terms of how the
brain intends to use the information-for short-term processingneeds,or as a referencethat will be usefulto soiveproblems in the future.
Haveyou everheard of the term "musclememory"? Perhapsvou're awarethat people
can ride a bike,swim, playthe piano,or demonstratea dancestepafternot doing
thoseactivitiesfcr many vea-rs.
Recentresearchindicatesthat nervefibersin the mus-
cles,and not just the brain, are actuallyinvolved in someof this long-term memory
storage.It's as though, with enoughrepetition,the bodywill storesignalsto make body
parts move in certain ways.That way,when the body is calledupon to do thosethings,
processingtime is faster.Youliterally can do things "without eventhinking about it."
MemoryStorage
Recallthe idea that both sidesof the brain are processingsensorydata about the
same thing at the same time, but in different ways.This theory regardinghow the
brain hemispheresboth specializeand synchronizewas presentedin the previous
textbook section.
The researchindicatesthat one systemhandlesthe detail workwhile the other creates a framework. The two systemsare called taxon arrdlocale memories.
Taxon memory handlesrote memorizationof data.Multiplication tables,spelling
words, and the bones of the hand are examplesof data that use the taxon memory
system.It requireseffort, such as repetition and practice,to storetaxon memories
(rote learning).
The locale memory system,on the other hand, storesmental maps.Theseare configurations of information connectedto eventsor associatedinformation (map learning).
MemoryRetrieval
The brain has the ability to withdraw information storedin taxon memory more
readily when they are storedaspart of one of the localememory system'smental
maps.Anything you can do to increasethe creation of a mentaj map, or schema,is
critical to long-term memory storage.
For example,continuous,repeatedpracticeis one way to aid memory and retrieval
capacity.Another method is to createassociationswith things you alreadyknow,to
takeyour understandingto a new level and enableapplication of the information in
more complexways.
Involving additional sensorysystemsis helpful to increaseretrievalpossibilities.
Somepeople find using body movementswill aid long-term storageand retrieval.
These"kinesthetic/tactilelearners"will recall a telephonenumber by repeatingthe
movementsneededto pressthe phone keys.Othersmight recalla rhythm or sound
pattern formed when sayingthe numbers out loud. We'll further exploretheseinteresting differencesin Lesson4, "Multiple Intelligences,"Iater in this chapter.
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Theabilityto solvea problemis onewayto defineintelligence.
Anotherwayto
is to talk aboutthe abilityto createsomethingor to contribute
describeintelligence
in a tangiblewayto one'ssocialsystemor culture.
Thesewordsdescribea greatdealof humanactivity.In fact,problemsolvingis one
wayexperiments
aredesigned
to testthe intelligence
of otherspecies.
Researchers
presenta taskto the animalandobservewhatresources
sheor hebringsto bearon
I
the "problem" of task completion.For example,monkeyshavebeen known to use
sticksto accessfood or plalthings.
The ability to solvea problem-from "the food is out of reach"to "how do we get to
the moon"-or the capacitl''to createa product is horvHoward Gardner defines
Thesecapabilitiesare considered
intelligencein his theoryof multipleintelligences.
distinguishingcharacteristicsof intelllgent life. For Gardnerto include a specific
problem-solvingstyleas a definedintelligence,the activirymust meet additional
criteria.For example,to make Gardner'slist, eachparticular intelligencemust have
to supportthat function.
specificregionsof the brain specialized
Note
in Cognitionand EduHoryardGardneris thetrohnH. andElisabethA. HobbsProfessor
cationat the HarvardGraduateSchoolof Education.HealsoholdspositionsasAdjunct
of Neurologyat the
Professorof Psychology
at llarvard University,AdjunctProfessor
BostonUniversirySchoolof Medicine,and Chairof the SteeringCommitteeof Project
go to
Zero.TolearnmoreaboutGardnerandhis theoryof multipleintelligences,
http:// wwmi nfed.orglthinkers/gardner.htm.
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Organismsthat do not takein sensorvinforrnation,processthat information, and
makedecisionsaboutwhat actionto takebasedon that informationare,by ciefinition, lessintelligent.The amoebathat takesin nutrientsasit driftsaround in the
supportfood intake in that
wateris not solvingproblems.Its biologicalprocesses
It
n'ould
not be capableof generit
rvould
die.
Without a food source,
enr.ironment.
ating anv options to enhancesurr.ival.
rvhen it comes to
You,on the other hand, arecapableof resourcefulingeniousness
For more information on this exciting subjeci,
solnng problems in order to surr.i'u,e.
Iaterin this chapter.
takea look at Lesson4, "MultipleIntelligences,"
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for how
Knowinghowthebrainfunctionsshouldgiveyou a betterunderstanding
we hurnansaresomuchalike,yetcanbehaveandreactto similarstimuli in completelydifferenlways.I(nowinghowyour brain worksmaymakeit easierfor you to
leam, communicate,and resolveconflict.
2. Name the three, n*ts of the brain.
3. Which part of the brain sensestime?
4. Explain how both sidesof the brain processsensorydata differentiy"