Brain and Its Functions Part 3 13436 (1)

8/3/2019 Brain and Its Functions Part 3 13436 (1)

http://slidepdf.com/reader/full/brain-and-its-functions-part-3-13436-1 1/50

Brain and Its Functions Part 3

Dr. Prithika Chary

Consultant Neurologist and Neurosurgeon

Adopted by Prof.K.Prabhakar,

[email protected]



Can We change Brain?

Many a times we are under the mistaken notion thatbrain goes through an irreversible process. Once itis formed we cannot change it. In reality the latest

research show that Brain is Plastic. You can changeyour brain physiology by constant learning.Therefore I am a sixty year old man, I cannotchange my profession or learn new skills is notcorrect. In fact a person at any given point of a time

in his life time subjected to having healthy organscan CHANGE HIS Or HER BRAIN.



Neuroplasticity

Is the lifelong ability of the brain to

reorganize neural pathways based on

new experiences



Can the brain change ?

Is it nature or nurture?

Twenty years ago we thought that the structure of the brain

develops during childhood and once that organization in thebrain has been developed that there is very little room forchanges and for plastic alterations.

Now we know that there is enormous capacity.

In addition to genetic factors, the brain is shaped by the

characteristics of a person's environment and by the actions of that same person.



PLASTIC – Ability to adapt Brain plasticity means the ability of the nervous

system to adapt to changed circumstances, tofind new ways of learning, sometimes after aninjury or a stroke, but more commonly when

you want to acquire a skill for, say, a hobby oreven a new job.

The ability of the brain to change withlearning is what is known as

neuroplasticity.



NEUROPLASTICITY Involves many processes

Involves changes

occurring throughoutone’s life

Involves all parts of thenervous system, neurons,

glia and vascular cells Is of four different types

as we know it today



NEUROPLASTICITYNeuroplasticity does not consist of a single type of

morphological change, but rather includes several

different processes that occur throughout an

individual’s lifetime.

Many types of brain cells are involved in

neuroplasticity, including neurons, glia, and

vascular cells.



Periods of rapid change or plasticity occur in

the brain under four main conditions:

Developmental plasticity: when the immature brain first

begins to process sensory information Activity-dependent plasticity: when changes in the

body, like a problem with eyesight, alter the balance of sensory activity received by the brain

Plasticity of learning and memory: when we alter ourbehavior based on new sensory information

Injury-induced plasticity: following damage to thebrain



While plasticity occurs over an individual’s

lifetime, different types of plasticity dominate

during certain periods of one’s life and are

less prevalent during other periods.During normal brain development when the

immature brain first begins to process sensoryinformation through adulthood (developmental

plasticity and plasticity of learning and memory).

As an adaptive mechanism to compensate for lostfunction and/or to maximize remaining functions

in the event of brain injury.



What are the basic processes

involved in brain development? Neurogenesis is the formation of neurons in the brain

Neural migration is the movement of neurons to

different areas of the brain Myelination, the covering of the neuron's axon with a

fatty sheath, allows neurons to conduct signals moreefficiently and protects the axon

Synaptogenesis is the formation of synapses, orconnections between neurons

Synaptic Pruning is the selective elimination of synapses



Developmental Plasticity: Synaptic

Pruning Over the first few years of life, the brain grows rapidly.

As each neuron matures, it sends out multiple branches

(axons, which send information out, and dendrites, whichtake in information), increasing the number of synaptic

contacts and laying the specific connections from neuron

to neuron.

At birth, each neuron in the cerebral cortex has

approximately 2,500 synapses.



Developmental Plasticity: Synaptic

Pruning By the time an infant is two or

three years old, the number of

synapses is approximately15,000 synapses per neuron(Gopnick, et al., 1999).

This amount is about twice that

of the average adult brain. Aswe age, old connections aredeleted through a process calledsynaptic pruning.



ACTIVITY DETERMINED

NEUROPLASTICITY Synaptic pruning eliminates weaker synaptic contacts

while stronger connections are kept and strengthened.

Experience determines which connections will bestrengthened and which will be pruned;

Connections that have been activated most frequently arepreserved.

Neurons must have a purpose to survive.

Without a purpose, neurons die through a process calledapoptosis in which neurons that do not receive or transmitinformation become damaged and die.



APOPTOSISApoptosis is called “ programmed cell death “

It takes place to avoid redundancy in the nervous

system

For the right cells to die/or less cells to die

nurturing the child’s brain is necessary with

adequate stimulation, because neurons that have

nothing to do will just literally kill themselves



APOPTOSIS The illustration shows a neuronundergoing a common form of apoptosis.

(A) The healthy neuron has adefined cell membrane and thecytoplasm and nucleus, which

contains DNA, are intact. (B) When apoptosis kicks in, the

cell contorts and the DNA breaksup.

(C) In the final stage of apoptosis,the cell is broken into membrane-bound pieces.

Specialized cells calledmacrophages or microglia removethe debris



Cortical MapsThe cortex contains maps

These maps represent our skills and our knowledge

of the world.

And the brain's mapmakers are kept very busy,indeed.

When a skill develops or changes, the corticalmaps also change, and neuron populations may beannexed for specific purposes, later abandoned,and sometimes annexed again.



The adult brain is driven by

behavioral experience We now know that the brain is plastic: it can and

does remodel itself, sometimes within a remarkablyshort period of time.

These biological changes in the adult brain aren'tdriven by developmental timelines or inherited traits.Instead, they are driven by behavioral experience

Just as the migratory behavior of residents can

change the map of a city, so can our learningbehavior change the maps in our brain, causingneurons populations to synchronize their actions,respond to new inputs, and support new skills.



Practice makes perfect When we approach learning seriously,

however, something else happens: we attend

to a task, we practice it over and over again,and we become emotionally involved.

Under these conditions, brain plasticityhappens - the winemaker can sharpen her

taste buds, the blind person can learn to readBraille, the musician can perfect his pitch, andyou can become an honest-to-goodness guitarplayer.



Selective attention Why are attention, repetition, and intensive

practice the prerequisites of brain plasticity?

Do we really have to listen to our teachers, goto class every day, and do homework everynight?

In 1890, philosopher and psychologist William

James wrote. My experience is what I agreeto attend to. Only those items which I noticeshape my mind - without selective interest,experience is an utter chaos."



space and time The crucial role played by the dimensions of

space and time doesn't end with our

behavioral experience. Brain maps change spatially by taking over

neighboring neuronal populations on differentparts of the cortex.

But brain maps can also change in time, bysynchronizing the actions of neurons moretightly so that a specific group of neuronsmay provide near-simultaneous responses to

the same input.



VersatilityThese timing relationships may actually

help support the plasticity of existing

cortical maps and the generation of newones, because a single neuron canparticipate in the representation of

several different sensory or motorrepresentations at different times.



Keeping in touch If we take a closer look at a single neuron and

its synaptic connections, we see that timing is

everything. Suppose a neuron sends weak, sporadic

chemical messages to the another neuron.

This situation is a bit like receiving postcards

once every few years from a long-lostacquaintance - the messages aren't alwayseffective enough to cause a sustained reactionin the second neuron



Weightlifting for the Mind: Enriched

Environments and Cortical Plasticity In the 1960's in Berkeley's biology labs,

Mark Rosenzweig and his colleagues

Edward Bennett, Marian Diamond, andDavid Krech made a proposition -- thatexperience can induce concrete andobservable changes in brain structure – This would profoundly influence ourunderstanding of education and thehuman mind for decades afterwards.



If negative early experiences could impairbrain development, could positive

experiences enhance the brain?

At Harvard, David Hubel and Torsten Wieselstudied cats raised blind in one eye, and by1962 they had demonstrated that suchdeprivation caused profound structuralchanges in the cats' visual cortex.

This work made it clear that severedeprivation during critical developmentalperiods could have catastrophic effects on agrowing brain, but the question of whetherthe opposite was true remained.



"cerebral exercise"

Rats raised in an "enriched" environment, with toysand social activities, were not only smarter than rats

raised in impoverished environments, but that theimprovement in performance correlated with anincrease in the weight of the rats' cerebral cortex.

The idea that the brain, like a muscle, might respondto "cerebral exercise" with physical growth was

surprising to many, and gave strength to anincreasingly powerful theory suggesting that allaspects of the mind - from memory, to dreams, toemotions - might have physical correlates.



Enriched Environments The brain expects, and

perhaps even depends upon,interaction with the

environment in order todevelop and reachmaturation.

Babbling may assist in thedevelopment of languagecapabilities, just as playingwith objects assists indevelopment of motor skills.



Enriched Environments

Children who are exposed to a rich andvaried education early in life develop a

great capacity for learning throughoutlife.

Real learning, not just rote exercise, can

have a dramatic influence on thephysical structure of the brain.



The orange dots represent the multiple

synapses on a single neuron.

The extent of synaptic

interconnectivity as we agedetermines our functional abilityto use our brains

In spite of losing neurons as weage, the densitiy of

interconnectivity makes up for theloss

This depends on continuous newlearning & environmentalenrichment

USE IT OR LOSE IT



Developmental Plasticity – synaptic

pruning Ineffective or weak connections are

"pruned" in much the same way a gardener

would prune a tree or bush, giving the plant

the desired shape.

It is plasticity that enables the process of

developing and pruning connections,allowing the brain to adapt itself to its

environment.



Plasticity of Learning and Memory

It was once believed that as we aged, the brain’s networksbecame fixed.

In the past two decades, however, an enormous amount of research has revealed that the brain never stops changingand adjusting.

Learning, as defined by Tortora and Grabowski (1996), is

“the ability to acquire new knowledge or skills throughinstruction or experience.

Memory is the process by which that knowledge isretained over time.



LEARNING The capacity of the brain to change with learning is

plasticity.

So how does the brain change with learning? According to Durbach (2000), there appear to be at least

two types of modifications that occur in the brain withlearning:

1. A change in the internal structure of the neurons, themost notable being in the area of synapses.

2. An increase in the number of synapses betweenneurons.



Learning WindowsDuring a child's development, there are a series of

time periods, or "windows," in which a child can

best learn or refine a particular ability, such as

speech.

After this time period is over it becomes much

more difficult, sometimes impossible, for the childto learn the same thing.



Myelination There are millions of neurons,

which form the electricalconnections that let us think.

These cells send their signalsthrough axons, some of which canreach a length of up to a meter inhumans.

Wrapped around many of the axons

are cells which form myelin sheaths,composed mainly of fat.

These sheaths serve to insulate theaxon, letting its signal travel about100 times faster than in anunmyelinated axon.





Myelination Myelinization is the key to

learning windows

Myelination is the major cause of theincrease in a child's brain size.

At birth, the infant brain weighs 300-350 grams (2/3 to ¾ pound).

In the first four years of life, the

brain increases to 80% of the adultweight of 1200-1500 grams (2.6 - 3.3pounds).

http://www.fcs.uga.edu/outreach/coopex/bbb/needtoknow/ch1/1_2faq2.htm

http://www.fcs.uga.edu/outreach/coopex/bbb/needtoknow/ch1/1_2faq2.htm



At birth… Few nerve centers are myelinated at birth.

In the beginning, only reflexes needed for

survival are completely myelinated

However, after birth the primary visual and

auditory cortex neurons rapidly receive their

myelination.



In childhood…

Myelination continues. During the first year-and-

a-half of life, the corticospinal motor tract receives

its myelination enabling gross control over arms,torso, and legs.

The brain continues to change and mature

during adolescence



During Adolescence…

Final myelination of the frontal lobes occurs inearly adolescence.

An adolescent's brain reaches the weight of anadult brain by about age fourteen due to myelinaccumulation and dendritic branching.

At this time the potential for contribution toinsight, judgment, inhibition, reasoning, and socialconscience are possible.



During Adolescence…

The adolescent's frontal lobes are increasingly active, and

this ability enables the adolescent to consider several

things in the mind while comparing or interrelating them. The density of synapses declines during adolescence

due to selective pruning of redundant or unused

connections.

Synapse formation continues despite ongoing pruning



Into Adulthood…

The brain continuously remodels itself-even into

adulthood.

Synapses continue to be formed in select areas

of the brain but growth of new neurons is

limited

Lifelong enrichment experiences are important



Injury-induced Plasticity: Plasticity

and Brain Repair During brain repair following injury, plastic changes are

geared towards maximizing function in spite of the

damaged brain. In studies involving rats in which one area of the brain

was damaged, brain cells surrounding the damaged areaunderwent changes in their function and shape that

allowed them to take on the functions of the damagedcells.

Although this phenomenon has not been widely studied inhumans, data indicate that similar (though less effective)

changes occur in human brains following injury.



Plasticity after amputation When nerve stimulation changes,

as with amputation, the brainreorganizes.

In one theory, signals from afinger and thumb of an uninjuredperson travel independantly toseparate regions in the brain's

thalamus (left). After amputation, however,

neurons that formerly respondedto signals from the finger respondto signals from the thumb (right).



Brains of human & animals



Babies start to babble around six to ten

months of age, and that not long afterwardthey say a few words like "no" or "uh-oh.“

At around two years, already more likechildren and less like babies, they beginspeaking grammatically correct sentences

and their vocabulary undergoes a growthspurt.

And by three years, most children canspeak in a manner that is essentially adult-

like.

LANGUAGE ACQUISITION



LANGUAGE ACQUISITION

Research has identified certain areas of the adult brainthat are typically responsible for specific aspects of language, and these can serve as starting points for

understanding children's brains. The left hemisphere appears to be critical in most right

handers and many left handers

Lesions to the right hemisphere are not usually

associated with language loss, but there is evidence thatthe right hemisphere plays a role in emotion

The right hemisphere has the potential to assume some

language functions if the left hemisphere is damaged.





BRAIN LATERALIZATION The term brain lateralization

refers to the fact that the twohalves of the human brain

are not exactly alike. Each hemisphere has

functional specializations:some function whose neuralmechanisms are localizedprimarily in one half of thebrain.



WHAT DOES HANDEDNESS HAVE TO DO WITH

BRAIN LATERALIZATION?

Most humans (70% to 95%)(but not all) have left

hemisphere specialization for language abilities.

5% to 30% have anomalous patterns of

specialization. These might include:

(a) having a right-hemisphere language

specialization or

(b) having little lateralized specialization.





Thank you and go to Part 4You will understand the application of Brain and

its Functions in the context of Management

disciplines.

Date post:	06-Apr-2018
Category:	Documents
Upload:	nur-hasina-mohd-ibrahim
View:	221 times
Download:	0 times

Brain and Its Functions Part 3 13436 (1)

Documents