Memory Physiology

7/31/2019 Memory Physiology

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Memory

Reference: chapter 57, 59.Dr. Samina Malik


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Definition of Memory:

Ability to store experiences & recall these

consciously or unconsciously.


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Types of Memory:

Immediate memory / short-term memory.

Intermediate memory.

Long term memory.


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Immediate memory / short-term

memory

Memory of some words, numbers or

information lasting for seconds to a few

minutes.

It is forgotten unless it is converted into

intermediate or long term memory.


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Example of short term / immediate

memory: A person consults a telephone directory for a

telephone number & then dials that number &forgets the number.

By immediate memory, we can take into mind 7or 10 digits of number.

It involves continuous neuronal activity.

Memory persists as long as impulses areconducted along nervous pathways.


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Mechanisms of immediate memory:

1) impulses travel along nervous pathways

having reverbrating circuits (impulses go

on travelling along same pathway again &

again).

2) pre-synaptic inhibition or facilitation.

3) post-tetanic facilitation.


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pre-synaptic inhibition or facilitation

At presynaptic terminal there are

additional synapses, which may be

inhibitory or facilitatory.


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post-tetanic facilitation

Through a synapse, impulses are rapidlyconducted, then a short rest is given & thenimpulses are again conducted through samesynapse.

Now response of post-synaptic neuron isgreater, due to more availability of calcium ions

in pre-synaptic terminal

release ofneurotransmitter EPSP Response by post-synaptic neuron.


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INTERMEDIATE MEMORY:

Memory of some words or information

lasting for hours, days or weeks.

It is difficult to be recalled & easy to be

forgotten, unless converted into long-term

memory.


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Example of intermediate memory:

We prepare for a test & keep it in mind for

weeks (if prepared well) & then forget,

unless we revise & convert it into long-

term memory.


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Mechanism of intermediate

memory:

There are temporary physical & chemical

changes at synapses & these include:

Increase in size & number of synaptic

knobs.

Increase in number of synaptic vesicles.


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Long-term memory:

Memory of words, numbers, information or

facts which last for years or throughout

life.

It is so consolidated that it can be recalled

rapidly. Difficult to be forgotten.


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Examples of long-term memory:

Alphabets,

names of near relatives,

certain facts about universe / religion.


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Mechanism of long-term memory:

To convert immediate or intermediatememory into long-term memory,consolidation is required, which involves

repetition or rehearsal.

Minimum consolidation may occur in 5-10

minutes & maximum occurs in 1 hr ormore, e.g., in Hifz-a Quran, same verse ofQuran is repeated.


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It involves changes at synapses which are

not temporary, but permanent.

There is increase in number & size of

synaptic terminals.

Increase in number of synaptic vesicles.


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Increase in number of released sites on

synaptic knobs.

There may be changes in post-synaptic

neurons.

It involves protein synthesis. Drugs which

inhibit RNA synthesis inhibit memory.


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During consolidation, synapses in thought

circuits are permanently facilitated to form

a memory trace, i-e., for certain facts in

our memory, there is a memory trace.


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In children, a number of extra-neuronal

pathways having synapses are available.

If these nervous pathways having synapses arefacilitated or used, these persist. If not used,

they degenerate. (Use it or lose it!)

That is why Hifz-a-Quran is more easy in

childhood. (budhay totay nahin sekhtay!)


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Parts of brain involved in memory

process:

1) Temporal lobe:

When different parts of temporal lobe are

stimulated, past events are recalled.

2) Hippocampi are involved in memory.

3) Thalamic nuclei are also involved.


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Loss of recent memory /

anterograde amnesia:

Site of lesion:

Hippocampi OR Anterior thalamic nuclei OR

Mamillary bodies OR

Dorsal medial nuclei of thalamus


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Loss of recent memory /

anterograde amnesia:

Clinical picture:

Past memory remains intact but recent memory

is lost.

These patients are not able to learn new events.

Not able to remember names & faces of person

they meet.


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Loss of past memory / retrograde

amnesia:

Lesion:

Lesion of certain thalamic nuclei.

Clinical picture:

Loss of past memory but able to store new

events.


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Drugs which stimulate memory:

Caffeine

Nicotine

Physostigmine Amohetamine

Strichnine

Metrazole


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ALZEIMERS DISEASE:

Premature aging of brain.

Loss of mental powers.

Disease starts at mid-adult age.

In severe cases, picture resembles mentalpower of a very old person.


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Etiology & Mechanism of

ALZEIMERS DISEASE: Thought to be hereditary.

Gene which controls formation of Apo-lipoprotein E (a blood protein that transportscholesterol to the tissues) is defective.

This protein is concerned with transport ofcholesterol in blood.

Deposition of amyloid material in brain (cerebralcortex, basal ganglia, hippocampus, thalamus,cerebellum). A metabolic degenerative disease.


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Etiology & Mechanism of

ALZEIMERS DISEASE:

Patients with Trisomy 21 (Down syndrome) have3 copies of the gene for amyloid precursorprotein & develop neurological characteristics of

Alzeimers disease by midlife.

Cerebrovascular disease caused byhypertension, atherosclerosis, diabetes,

hyperlipidemia may play a role.

Main clinical feature is loss of memory.


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Working memory:

Includes mainly short-term memory.

Is used during the period of intellectualreasoning.

Terminated as each stage of problem isresolved.


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Classification of memories on the basis of

the type of information stored:

Declarative memory:

Memory of various details of anintegrated thought, like memory ofan important experience including:

Memory of surroundings, time relationships,

causes of the experience &

ones deductions / conclusionsthat were left in the persons mind.

Skill memory:

Associate with motor activity likeskills developed for hitting atennis ball, including automaticmemories to:

1) Sight the ball2) Calculate the relationship &

speed of the ball to racquet

3) Deduce rapidly the motion of thebody, arms & racquet to hit theball as desired.

This skill memory is based onprevious learning of the game-then moving on the next stroke ofthe game while forgetting thedetails of the previous stroke.


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Habituation:

A type of negative memory.

Brain can ignore the information with no

consequence.

Mechanism involved is inhibition of synaptic

pathways for this type of information.

Resulting effect is called habituation.


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Memory sensitization:

A type of positive memory.

Brain enhances & stores the memory traces that haveimportant consequences like pain or pleasure.

Mechanism is facilitation of synaptic pathways.

Special areas in basal limbic region of brain determine

whether the information is important or not & make thesubconscious decision whether to store the thought as asensitized memory trace or to suppress it.

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Memory Physiology