memory physiology
TRANSCRIPT
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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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Mechanism of long-term memory:
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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Mechanism of long-term memory:
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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Mechanism of long-term memory:
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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Mechanism of long-term memory:
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.