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8/12/2019 Lear Rning

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R.A ISHVARYA


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Higher intellectual functions are veryessential to make up human mind.

These functions are also called as higherbrain functions or higher cortical functions.

Cerebral cortex is responsible for thesefunctions.


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Cerebrum is the largest part of the brain. It has 2 hemispheres- right & left.

The superficial part of the cerebrum is

composed of nerve cell bodies or gray matterforming cerebral cortex.

The deeper layers consists of nerve fibers orwhite matter.


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1. LAYER 1 - stellate cells( star shaped cells)2. LAYER 2 -small pyramidal & stellate cells.

3. LAYER 3 -typical pyramidal cells.

4. LAYER 4 -densely packed stellate cells.5. LAYER 5 -giant pyramidal & betz cells.

6. LAYER 6 -different types of cells.


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Each cerebral hemisphere consists of 4 lobes;1. Frontal lobe

2. Parietal lobe

3. Occipital lobe4. Temporal lobe.


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A revolution in our understanding of brainfunction in humans has been brought aboutby the development of positron emissiontomographic PET) scanning, magneticresonance imaging MRI).

PET scans are used to identify particular areasfor speech, hearing etc.


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It is defined as the process by which newinformation is acquired.

It alters the behaviour of a person on thebasis of past experience.


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It is classified into 2 types:

1. Non-associative learning-habituation,sensitization.

2. Associative learning


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During habituation there is a decrease in theCa2+ level in the presynaptic terminal whenrepeated stimulus is given.

Low Ca2+ concentration is responsible forthe less amount of stimulating neurotransmitter.


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Finally the person is habituated to thestimulus and ignores it.

For example, a political slogan, cinema songetc

2) Sensitization:

It is a process by which the body is made tobecome more sensitive to a stimulus.

It is called amplification of response.


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For example, a woman is sensitized to cryingsound of her baby.

While sleeping, she suddenly wakes up whenher baby cries because of sensitization tocrying sound of the baby.


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When a stimulus is given repeatedlyserotonin released by nociceotive (causingpain) neurons prolongs the Ca2+ influx in tothe presynaptic neurons.

This in turn leads to increased release ofneuro transmitters that stimulate the postsynaptic neuron frequently.


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It is a complex process. It involves learning about relations between 2

or more stimulus.

Classic example is conditioned reflex.

Conditioned reflex is important in all forms oflearning.

For example, sugar put into mouth always

causes salivation. Sugar- unconditioned stimulus.


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But if a sound is given before putting sugarand made as a practice, it is seen that thesound in absence of sugar can stimulatesalivation.

Normally sound causes no salivation but onassociation with unconditioned stimulusgives a response.

This is called associative learning.


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It is defined as the ability to recall pastexperience or information.

Some memories remain only for few seconds,while others lasts for hours, days, months oreven years together.


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The structure for memory is synapsein thebrain.

Synapse for memory coding is different fromother synapse.

2 separate presynaptic terminals are presenthere.

one post synaptic neuron is present here.


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One of the terminals is primary pre synapticterminal, which ends on post synapticneuron.

This terminal is called sensory terminal, assensations are transmitted to the postsynaptic neuron by this terminal.

Another presynaptic terminal ends on sensory

terminal itself. This is called facilitator terminal.


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Memory is stored in brain by the alteration ofsynaptic transmission between the neuronsinvolved in memory.

Storage of memory may be habituated or

facilitated. When sensory terminal is stimulated alone

without facilitator terminal, it leads tohabituation firing decreases slowly.

If both terminals are stimulated, facilitationoccurs-signal remain for few months toyears.


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Hippocampus Thalamus

Hypothalamus

Corpus striatum are the main sites ofencoding.

Frontal & parietal lobes are also involved,


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Previously mentioned mechanisms onhabituation and sensitization are provedexperiments done on sea snail (Aplysia).

Nobel laureate, Eric kandel worked on this.

This animal is useful in brain researchbecause of its simple nervous system & theindividual nerve cells are large.


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A) SHORT TERM MEMORY:

It is the recalling of events that happenedvery recently i.e within hours or days.

Basic mechanism of short term memory isthe formation of new neuronal circuits thrunew synapses and facilitated neuronal

transmission. Confined to single storage area.

Interrupted by drug, stress & trauma.


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B) LONG TERM MEMORY: it is the recalling of events of weeks, months,

years or lifetime.

For example- poem memorized in schooldays.

The neuronal circuits are activated constantlymemory is consolidated & encoded into

different areas in brain. This makes them permanent memory.


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C)EXPLICIT MEMORY: It is the memory involving conscious

recollection of past experience

Also called as declarative memory.

It involves hippocampus and medial part oftemporal lobe.

Example- recollection of birthday party

celebrated 3 days ago.


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D) IMPLICIT MEMORY: It is defined as the memory in which past

experience is utilized without consciousawareness.

Also called skilled memory.

Example- cycling, driving etc

It involves the sensory and motor pathways.


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Stimulation of facilitator neuron & sensoryneuron.

Release of serotonin from facilitator terminalon sensory terminal.

Formation of serotonin- receptor complex.

Activation of adenyl cyclase.

Formation of cAMP in sensory terminal.

Activation of protein kinase.


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Phosphorylation of K+ in the terminalmembrane.

Blockage of K+ exit.

Continues action potential for long period.

Continues influx of Ca+ in sensory terminal.

Release of large amount of neurotransmitter.

Facilitation of synaptic transmission and

memory.


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Common stimulants; Caffeine

Physostigmine.

Amphetamine.

Nicotine.

Strychnine.

Metrazol.


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1) AMNESIA: Loss of memory.

2 types;

Anterograde- failure to establish new longterm memories due to lesion inhippocampus.

Retrograde- failure to recall past long term

memory due to temporal lobe syndrome.


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2) DEMENTIA: A progressive deterioration of intellect,

emotional control, social behaviour, andmotivation associated with loss of memory.

It is an age related disorder.

Usually occurs above age 65.

If it occurs under age of 65 pre senile

dementia.


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CAUSES: Common cause- Alzheimers disease.

Hydrocephalus, huntington chorea,parkinsonsdisease, viral encephalitis, HIVinfection, hypothyroidism, hypo parathyroidism, cushing syndrome, alcoholicintoxication, barbiturate poisoning, CO,heavy metals etc.


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CLINICAL FEATURES: loss of recent memory, lack of thinking.

Judgement & personality changes.

As disease progress-psychiatric & motorchanges.

Physostigmine drug- moderate improvement.


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3) ALZHEIMERS DISEASE: Progressive neurodegenerative disease.

Loss of neurons by death in cerebralhemispheres, pons, hippocampus.

Reduction in synthesis of acetycholine due tolack of enzyme choline acetyl transferase.

Dementia is the common feature.

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